Glimpses of the Past is an insight into India’s history before Independence. It gives readers an understanding into what led to India’s freedom struggle.
When the British first set foot on the Indian soil, they had no plans of invading their country. All they wanted to do was to establish trade for their livelihood. However, they soon noticed loopholes in the administration by Indians and used this to their advantage. They took control over the country and enforced various laws that affected the livelihood of Indians in their own motherland.
But, things took a different turn when India witnessed the rise of various people like Raja Ram Mohan Roy. Inspired by them, Indians started their revolt against the British and marked the herald of the Great Revolt of 1857. All this and more noteworthy episodes of India’s struggle for freedom are highlighted in Glimpses of the Past.
The Glimpses of the Past Summary in English
The Glimpse of the Past is in the form of conversation dealing with India’s struggle for Independence. It is written by S. D. Sawant. The chapter describes the events and the circumstances that took place in India during the year 1757 to 1857. It starts with the time when the East India Company was very strong in India.
The Indian princes and states were busy fighting with each other. They often sought British help and thus British took advantage of this to gain power and establish their rule in India. The social conditions were also not in good shape. Social evils such as child marriages, untouchability, sati pratha, etc. were prevalent in society. Also, the farmers had to pay heavy taxes.
Raja Ram Mohan Roy worked a lot towards reforming society. British also passed many resolutions to ruin India and Indian industries. Lord Macaulay also brought a bill according to which the medium of education could only be English.
The main aim of the British was to prepare clerks who can assist them in the administration. By 1856, India had fully become a British colony. However, after the revolt of 1857, the British rule started to shake. The Indians revolted and struggled for freedom until 1947, i.e. till they achieved it.
The chapter starts with the events that were taking place in the year 1757. At this time, the British were in a strong position in India. They had superior arms and ammunitions and also financial resources. On the other hand, the Indian states and the princes were short-sighted and were busy fighting with each other. They lacked unity. They also often sought British help and East India Company took full advantage of this.
The British followed the policy of ‘Divide and Rule’ and also subdued the Princes. Some people favoured the British while some did not. However, Tipu Sultan of Mysore fought with the British. But unfortunately, he died in the year 1799 fighting the Fourth Anglo-Mysore War.
The chapter further describes the social fabric from 1765 to 1836. Evil social practices such as untouchability, child marriages, Sati pratha, etc. were preached by the religious leaders. The British disdained the Indians and, in the process, Indians lost their self-respect also. The British imposed heavy taxes on the farmers. They also cut the thumbs of the expert artisans. However, the imports from England were tax-free. Thus, the main motive of the British was the maximisation of profit and wealth at any cost.
From 1772 to 1833, Raja Ram Mohan Roy started his efforts to reform Indian society. He established Brahmo Samaj for this purpose. He propagated the idea that the main teachings and principals of all religions are the same. Also, he started newspapers in India. He was against evil practices such as Sati pratha, polygamy, child marriages, and the caste system. He played a major role in the abolishment of Sati pratha.
In 1818, the British passed The Third Regulation Act. According to it, an Indian could be sent to jail even without any trial in the court. This was a phase of oppression of the Indians. By 1829, the value of British exports was worth seven crore rupees. While the Indian industries were ruining, the British were prospering.
It seems this was not enough so the British now aimed at preparing clerks for running the administration. Thus, in 1835, Lord Macaulay recommended that the medium of education should be English. This education policy also generated some intellectuals who understood the evils of British Raj and educated the fellow Indians.
By 1856, India had become a fully controlled British Colony. The suppression was at its peak and thus it led to revolts. In 1855, the Santhals rebelled and killed the British as well as their servants. In 1857, the first Sepoy Mutiny started with the execution of Mangal Pandey.
The sepoys marched towards Delhi shouting slogans in favour of Bahadur Shah Zafar. The landlords also joined this movement. People circulated chapattis with the message that their native ruler needs their help. Similarly, a lotus flower was distributed among the Indian soldiers.
Many rulers like Hazrat Mahal of Lucknow, Maulvi Ahmadullah of Faizabad, Tatya Tope, and Peshwa Nana Saheb of the Maratha empire and Kunwar Singh of Bihar also joined the revolt. This was the beginning of the Indian freedom struggle.
The Glimpses of the Past Summary in Hindi
यह एक चित्रकथा है। यह स्वतन्त्रता संग्राम की गाथा को चित्रों द्वारा दर्शाता है। इसमें यह वर्णन किया गया है कि 1857 के पहले स्वतन्त्रता संग्राम किन कारणों से शुरु हुआ था। दिल्ली के एक समारोह में लता मंगेस्कर ने एक देशभक्ति का गीत, ऐ मेरे वतन के लोगों गाया था। उसने भारत के लोगों को आंसू भरी आंखों से भारतीय स्वतंत्रता सेनानियों के प्राणों की आहुतियों को याद करने का आग्रह किया।
अंग्रेजी ईस्ट इण्डिया कम्पनी भारत में व्यापार के सिलसिले से आई। पर अपने उत्तम एवं कूटनीतिक कौशल द्वारा उसने 18वीं शताब्दी में अपना प्रभुत्व फैला लिया। भारतीय राजा आपस में विभाजित तथा संकीर्ण दृष्टिकोण वाले थे। लोगों को राज्यों के बीच निरन्तर होने वाली लड़ाइयों के कारण शांति नहीं मिल पा रही थी। उन्होंने अंग्रेज सौदागरों की मदद माँगी ताकि एक दूसरे को नीचा दिखा सकें। आपसी प्रतिद्वन्द्विता ने कम्पनी का रास्ता साफ कर दिया। एक-एक करके उसने भारतीय नवाबों पर अपना अधिकार जमा लिया।
दूरदृष्टि वाला एक वीर मैसूर का शासक टीपू सुल्तान अंग्रेजों से युद्ध करते हुए शहीद हो गया। भारतीयों ने अब अंग्रेज कम्पनी की विजय यात्रा को स्वीकार कर लिया। कुछेक ने तो परमात्मा तथा कम्पनी दोनों का आभार व्यक्त किया कि उन्होंने ठगों की लूटपाट रोककर देश में शांति स्थापित की। वे कहने लगे की भारत कि किस्मत अंग्रेजों के साथ जुड़ी है। पर कुछ अन्य व्यक्ति दुखी हो गये। उन्होंने शिकायत की कि गोरे लोग या तो राजाओं की हत्या कर रहे हैं अथवा उनसे उनकी राजसत्ता छीन रहे हैं। भारतीय गोरों के दास बनते गये।
कुछ धार्मिक नेताओं ने सामाजिक बुराइयों जैसे छुआछूत तथा बाल विवाह का समर्थन किया। उन्होंने समुद्री यात्रा करके देश से बाहर जाने को मना कर दिया। कुछेक बोले कि सभी कष्टों की जड़ महिलायें हैं। सच यह था कि भारतीय आत्मसम्मान खो चुके थे। अंग्रेज उन पर अविश्वास करते थे तथा उनसे घृणा करते थे।
अंग्रेज मूलरुप से सौदागर थे। उनका लक्ष्य था तेजी से धन कमाना। उन्होंने किसानों पर भारी कर लगा दिए तथा कर न देने पर उन्हें जेल भेज देते थे। उन्होंने भारतीय कुटीर उद्योगों को खत्म कर दिया ताकि वे इंग्लैण्ड में निर्मित सामान भारत को निर्यात करते रहें। उन्होंने इंग्लैण्ड से आयात किये सभी प्रकार की चीजों को कर मुक्त कर दिया। इस प्रकार उन्होंने भारतीय कारीगरों एवं व्यापार को नष्ट कर दिया।
राजा राम मोहन राय बंगाल के एक विद्वान एवं समाज सुधारक थे। उन्होंने समझ लिया कि देश में क्या कमी है। उन्होंने लोगें से कहा कि अपनी पुरानी संस्कृति पर गर्व करो तथा समाज को मूर्खतापूर्ण अंधविश्वासों से छुटकारा दिलाओ। उन्होंने बताया कि सभी धर्म एक ही शिक्षा देते हैं। उन्होने विज्ञान एवं आधुनिक ज्ञान के महत्त्व को पहचाना। उन्होंने अखबार प्रकाशन शुरु किया पर अंग्रेजों ने 1823 में उन्हें बंद कर दिया। वह समुद्र पार करके इंग्लैण्ड गये, यह पता लगाने कि किस कारण अंग्रेज इनसे बलशाली हो गये। उन्होनें फिर मध्यमार्ग अपनाया। उन्होने अंग्रेजों को शासक के रुप में स्वीकार कर लिया। पर उन्हें यह बताया कि उन्हें याद रखना चाहिए कि एक शासक का अपनी प्रजा के प्रति क्या उत्तरदायित्व होता है।
1765 से 1835 तक अंग्रेज भारतीयों पर अत्याचार करते रहे। 1818 में उन्होंने एक प्रस्ताव पारित किया जिसके अनुसार वे किसी भी भारतीय को बिना मुकदमे के जेल भेज सकते थे। भारत में अंग्रेज अफसरों को ज्यादा वेतन मिलता था तथा वे अपने निजी व्यवसाय द्वारा भी धन कमाते थे। अंग्रेज समृद्ध होते गये पर भारतीय उद्योग बन्द होने लगे। गवर्नर जनरल बेन्टिक ने इंग्लैण्ड लिखकर भेजा कि भारतीय कपड़ा उद्योग में लगे कारीगर भूख से मर रहे हैं।
भारतीयों को फारसी तथा संस्कृत पढायी जाती थी। 1835 में मैकाले नामक व्यक्ति ने अंग्रेजी शिक्षा की सिफारिश की। अंग्रेजी शिक्षा ऐसे क्लर्क बनाने लगी जिन्हें छोटी-छोटी नौकरियाँ मिल जाती थीं। पर अंग्रेजी शिक्षा ने बुद्धिजीवियों को भी पैदा किया जिन्होंने कहा कि भारतीयों को अंग्रेजी पढ़ना चाहिये, जिससे वे अपने आर्थिक स्थिति तथा शिकायतों को ब्रिटिश संसद में भेज सकें।
1856 तक अंग्रेजों ने पूरे भारत को अपने अधीन कर लिया था। उन्हें भारतीयों की कुशलता की तो चिन्ता थी ही नहीं। भारतीय राजा और शासक उनके हाथ की कठपुतली बन गये थे। लोगों से उनके काम, धाम और उनकी भूमि-सब कुछ छिन गई थी। उन्हें लगा कि अंग्रेजों को भारत से खदेड़ना जरुरी है। संथालियों ने 1855 में विद्रोह कर दिया और बहुत से यूरोपियन लोगों की हत्या कर दी। अंग्रेजी सेना में जो भारतीय सैनिक थे, उनमें भी असंतोष पनप रहा था क्योंकि उनको वेतन कम मिलता था। उन्हें देश के बाहर भेज दिया जाता था। सिपाही मंगल पाण्डे ने गोरे अफसर पर हमला कर दिया जिससे उसे फाँसी पर लटका दिया गया।
हजारों अन्य सिपाहियों को भी जंजीर से बाँध दिया गया। कुछ ब्राह्मण सैनिकों को पता चल गया कि उनकी गोलियों में गायों तथा सुअरों की चर्बी लगी है। विद्रोह के लिये तैयार रहने हेतु हर गांव में संदेश भेज दिया गया। मेरठ में हिंसात्मक कार्यवाई शुरु हो गई। सिपाही दिल्ली की ओर कूच कर गये तथा सम्राट बहादुर शाह को अपना नेता मान लिया।
विद्रोह फैलता गया। अनेक जमींदार भी इसमें शामिल हो गये। लखनऊ की बेगम हजरत महल, अजीमुल्ला खान, पेशवा नाना साहव, बिहार के कुँअर सिंह-सब ने पूरे उत्तरी भारत में अंग्रेजों से डटकर लड़ाई की। बरेली, कानपुर तथा इलाहाबाद में भी लोग भड़क गये। इस प्रकार से भारत का पहला स्वतंत्रता संग्राम शुरु हो गया।
Tsunami’ refers to a very large and powerful wave in the sea. It is caused by some earthquake under the sea. One such calamity hit several countries on December 26, 2004. The worst affected parts were coastal parts of India, the Andaman and Nicobar islands and Thailand. Some 1,50,000 people lost their lives. But animals suffered very few casualties. Perhaps they had sensed the coming earthquake and they ran to safer high places.
This lesson recounts a few stories of bravery and intelligence when the Tsunami hit the Andamans. The first story is about ignesious, the manager of a cooperative society in Katchall. He was woken up by his wife at 6 am. The family rushed out of the house. When the earth stopped shaking, the sea started rising. The waves washed away his two children and in-laws. But his three other children were saved because they were with him.
The Tsunami Summary in English
Andaman and Nicobar Islands
The Tsunami chapter of Class 8 comprises of three parts. This chapter deals with the inspiring incidents that took place when the Tsunami hit the different parts of the world. The first part includes stories from the Andaman and Nicobar Islands. The first story is of Igneous. He was the manager of a co-operative society in Katchall. At around 6 a.m., his wife woke him up sensing an earthquake. He put the television set on the floor in order to save it while the family rushed out of the house. When the earth stopped shaking, they could see the sea rising. The tsunami swept his wife, two children, father-in-law, and brother-in-law.
The second story is about a policeman, Sanjeev. Sanjeev was able to save himself, his wife, and his daughter. But, after hearing the cries of the guest house cook John’s wife, he jumped into the water in order to save her. He could not save her as well as himself and both got drowned.
The third story is about a 13 years old girl, Meghna. The tsunami swept her along with her parents and seventy-seven other people. But fortunately, she held on to a wooden door. After floating for two days, a wave brought her back to the shore and saved her. The last story is about Almas, a ten years old girl. Her father saw the water receding after the tremors and understood that it will come back with immense force. He thus woke everybody so that they can go to a safe place. In all this chaos, her grandfather fell down and her father went to help him. A big wave swept them away during this. Her mother and aunts swept away along with the tree that they were holding on to. While Almas climbed on a floating wooden log and fainted. She was taken to the hospital in Kamorta.
Thailand
The second part of the chapter consists of a story from Thailand. This is the story of an intelligent girl, Tilly. It was 26th December and Tilly along with her family were on the beach. Tilly and her family were originally from England and had come to Thailand to celebrate Christmas. Tilly and her mother saw the sea rise slowly, start to foams, and making whirlpools. Her mother was not worried by these signs but it occurred to Tilly that these were the signs of Tsunami. She informed about this to her family and they along with other people on the beach returned to the hotel. Luckily, the hotel building withstood the force of Tsunami and they all were saved.
The third part of the chapter speaks about the sixth sense of the animals. Around 1,50,000 people lost their lives but only a few animals died. For instance, in the Yala National Park situated in Sri Lanka, 60 visitors died while only two animals died. Also, in the same park people noticed that three elephants ran away from the beach an hour prior to the struck of Tsunami. Another incident is also from Galle in Sri Lanka. Here, the two dogs refused to go to the beach for the walk. Their master also thus could not go and was saved.
The Tsunami Summary in Hindi
Andaman and Nicobar Islands
सुनामी समुद्र में उठने वाली बहुत विशाल, शक्तिशाली लहर को कहते हैं। यह समुद्र के अन्दर आने वाले भूचाल के कारण उठती है। ऐसी एक विपदा 26 दिसम्बर 2004 में कई देशों पर आई थी। सर्वाधिक कहर वाले स्थान थे भारत के कुछ समुद्री तटीय भाग, अंडमाननिकोबार द्वीप समूह तथा थाइलैण्ड लगभग डेढ़ लाख लोगों की जानें गई। पर पशुओं के मरने की संख्या बहुत कम रही। शायद वे आने वाले भूचाल को पहले से महसूस कर लेते हैं और सुरक्षित ऊँचे स्थानों पर चले जाते हैं।
यह पाठ ऐसी ही सुनामी प्रभावित अंडमान में बहादुरी एवं बुद्धिमत्ता दर्शाती कहानियों का विवरण देता है। पहली कहानी है इग्निसियस की जो कैचल में एक सहकारी संस्था का मैनेजर था। 6 बजे प्रात: उसकी पत्नी ने उसे जगाया। परिवार घर से बाहर भाग निकला। जब धरती का हिलना थमा, तो समुद्र की सतह में उफान आने लगा। लहरें उस व्यक्ति के दो बच्चों और ससुर एवं सास को बहा ले गईं। पर उसके दूसरे तीन बच्चे बच गये क्योंकि वे उसके साथ थे।
संजीव एक सिपाही था। उसने स्वयं को, अपनी पत्नी तथा लड़की को लहरों से बचा लिया। पर जब वह अपने रसोइया की पत्नी को बचाने गया तो दोनों को ही लहरें बहा ले गई।
13 वर्षीय मेघना को भी उसके माता-पिता एवं 77 अन्य लोगों के साथ लहरें बहा ले गई थीं। पर मेघना दो दिनों तक एकलकड़ी के दरवाजे पर बैठी भटकती रही। 11 बार राहत पहुंचाने वाले हेलीकॉप्टर उसके ऊपर से गुजरे पर वे उसे देख नहीं पाये। अंत में एक लहर ही उसे तट पर पहुँचा गई।
अल्मास जावेद 10 वर्ष की पोर्टब्लेअर स्थित कान्वेट स्कूल की छात्रा थी। उसका परिवार क्रिसमस मनाने दूसरे टापू पर गया था। अल्मास के पिता ने सबेरे समुद्री लहरों को पीछे हटते देखा। वह समझ गया कि ये लहरें पूरे वेग से वापस लौटेगी। उसने अपने परिवार को सुरक्षित स्थान पर ले जाने की चेष्टा की। परन्तु उसके पिता तथा दादा को एक विशाल लहर द्वारा बहा कर ले जाया गया। उसकी मां और चाचियों को भी लहरें बहा ले गई। अल्मास स्वयं एक लकड़ी के गट्टे पर चढ़कर बैठ गई। बाद में उसने स्वयं को अस्पताल में भर्ती पाया।
Thailand
एक घटना है थाइलैण्ड की। स्मिथ परिवार एक तटीय रिजार्ट में क्रिसमस मना रहा था। माता-पिता तथा उनकी दो बेटियाँ थीं। 26 दिसम्बर 2004 को समुद्र जल अन्दर आने लगा। पर छोटी लड़की टिल्ली ने आने वाले खतरे को पहले ही भांप लिया। उसे अपना भूगोल का पाठ याद आया जिसमें लिखा था कि भूचाल, ज्वालामुखी तथा भूस्खलन के कारण सुनामी का जन्म होता है, उसने परिवार के सदस्यों को आवाज दी कि तट से भाग चलो। उसके माता-पिता होटल की तीसरी मंजिल पर चले गये और बच गये। इस प्रकार भूगोल के पाठ की जानकारी ने उनकी प्राण रक्षा कर दी।
मनुष्य तो अपने प्राण खो बैठते हैं, जबकि वन्य तथा पालतू पशु समय रहते खतरे को महसूस कर लेते हैं। हाथी ऊँचे स्थान पर भाग गये और कुत्तों, पक्षियों तथा जीवोद्यान के पशुओं ने सुरक्षित स्थान खोज लिये। शायद पशुओं की एक छठी इंद्रिय होती है। वे झटकों को मानवों से कहीं पहले महसूस कर लेते हैं। इसके कारण उनके हताहत होने की संख्या बहुत कम रहती है। लंका स्थित याला नेशनल पार्क में किसी भी पशु के हताहत होने का समाचार नहीं मिला जबकि 60 पर्यटक सुनामी के शिकार हो गये।
The narrator of the story went to a junk shop and purchased a roll-top desk which was in bad condition. The narrator started its repairing on Christmas Eve and found a letter in its drawer. He read the letter. It was from Jim Macpherson to his wife Connie as written on top. After reading the letter, he found that Jim Macpherson was the leader of the England Army and he described that England and German were engaged in a war but on the Christmas morning a wonderful thing happened, first Germans wishes happy Christmas to English soldiers and same response was given by English also. The leaders shared their ideas and feelings with each other and celebrated Christmas by eating, laughing, talking and drinking. After that they played football match in which Germans won. In the night both troops sang carols and had a peaceful Christmas.
The author decided to gave this letter to Jim’s wife back. He went to the address which was written on the letter envelope where he found that an accidental fire caught in the house and she was in nursing home. He rushed to nursing home where he found Jim’s wife. As she was grown too old in the waiting of his husband he mistook the author by understanding him as Jim, his husband when narrator met him. She declared him as best Christmas present in the world.
Summary of the Chapter in Hindi
कहानी का वर्णनकर्ता एक कबाड़ की दुकान में गया और एक रोल-टॉप डेस्क खरीदा जो खराब स्थिति में था। वर्णनकर्ता ने क्रिसमस की पूर्व संध्या पर इसकी मरम्मत शुरू की और इसकी दराज में एक पत्र मिला। उसने पत्र पढ़ा। यह जिम मैकफर्सन से लेकर उनकी पत्नी कोनी तक के रूप में शीर्ष पर लिखा था। पत्र पढ़ने के बाद, उन्होंने पाया कि जिम मैकफर्सन इंग्लैंड की सेना के नेता थे और उन्होंने वर्णन किया कि इंग्लैंड और जर्मन एक युद्ध में लगे हुए थे लेकिन क्रिसमस की सुबह एक अद्भुत बात हुई, पहले जर्मनों ने अंग्रेजी सैनिकों को क्रिसमस की शुभकामनाएं दीं और उसी प्रतिक्रिया अंग्रेजी द्वारा भी दिया गया था। नेताओं ने एक-दूसरे के साथ अपने विचारों और भावनाओं को साझा किया और खाने, हंसने, बात करने और पीने के द्वारा क्रिसमस मनाया। उसके बाद उन्होंने फुटबॉल मैच खेला जिसमें जर्मनों की जीत हुई। रात में दोनों सैनिकों ने कैरल गाया और शांतिपूर्ण क्रिसमस मनाया।
लेखक ने यह पत्र जिम की पत्नी को वापस देने का निश्चय किया। वह उस पते पर गया जो पत्र के लिफाफे पर लिखा था, जहां उसने पाया कि घर में अचानक आग लग गई और वह नर्सिंग होम में थी। वह नर्सिंग होम पहुंचे जहां उन्हें जिम की पत्नी मिली। जैसे ही वह अपने पति की प्रतीक्षा में बहुत बूढ़ी हो गई थी, उसने लेखक को जिम, अपने पति के रूप में समझकर उसे गलत समझा जब कथाकार उससे मिला। उसने उसे दुनिया का सबसे अच्छा क्रिसमस उपहार घोषित किया।
When the water present on earth in the oceans, seas, rivers, lakes, ponds and under the ground gets contaminated, it is termed as water pollution. The contamination of water results in a change in its physical, biological and chemical properties and hence makes it unsafe for drinking or usage of other purposes. The substances that cause water pollution are called Water Pollutants. The pollution of water can lead to serious effects such as diseases, an effect on the ecosystem of a region, and loss of aquatic life.
Major Water Pollutants
Sewage: a massive amount of wastewater or sewage is dumped into water bodies such as rivers and seas which pollutes their freshwater and makes it inappropriate for any kind of consumption due to the rise of several bacteria and other microorganisms. It not only affects the aquatic life of the water body but also leads to severe diseases like cholera, diarrhoea and typhoid.
Industrial Chemical Wastes: Harmful chemicals such as lead and mercury are often dumped by industries into the water bodies directly which contaminate their water.
Agricultural Effluents: Fertilizers, pesticides, insecticides and farm wastes are often washed off by the rain to the water bodies and contaminate the water.
Oil Spills: Oil spills often occur due to accidents and leakages of oil in the sea which leads to loss of aquatic life.
Thermal Wastes: Thermal industries often spill warm water in the water bodies which decreases its oxygen content. It also leads to a rise in temperature of water which is not suitable for aquatic animals.
Suspended Solids: They come from soil erosion, untreated sewage and mining. These suspended pollutants block the sunlight from reaching the aquatic plants and animals.
Organism
Diseases
Remarks
Ascaris sp.
Nematode worms
Danger to man from polluted water and dried sludge used as a fertilizer.
Bacillus anthracis
Anthrax
Found in waste water spores are resistant to treatment.
Brucella sp.
Brucellosis, Malta fever in man, contagious abortion in sheep, goat and cattle.
Transmitted by infected milk by contact, by waste water.
Entameoba histolytcca
Amoebic dysentery
Spread by contaminated water.
Leptospira sp.
Leptospirosis (Well’s Diseases)
Caused by sewer rats.
Mycabact, tuberculi
Tuberclosis
Isolated from waste water
Salmonella paratyphi
Paratyphoid fever
Common in waste water
Salmonella typhi
Typhoid fever
Common in waste water
Salmonella sp.
Food poisoning
Common in waste water
Shigella sp.
Bacillary dysentery
Polluted water
Vibrio cholarae
Cholera
Polluted water
Virus
Poliomyelitus hepatitis
Waste water treatment plants
E. coil
Diarrhoea
Polluted water
What is wastewater?
The water that has been used and is not fit for usage again is called Wastewater. It is dirty water from the laundry, toilets, sinks and drains.
Water – Our Lifeline
Figure 1: Usage of clean water
We all need clean water however, not all can access the same.
Hence, it is necessary not only to preserve water but clean the used water before dumping it into the seas or any other water body.
This is why the United Nations proclaimed the period between 2005 and 2015 as the International decade for action on ‘water for life’.
What do you mean by cleaning of water?
It is a process in which the pollutants from the water are removed before the water reaches a water body or before it is used again. This process is also called Sewage Treatment.
What is sewage?
Wastewater from houses, offices, Industries, hospitals and other sources is called Sewage.
Rainwater that flows into the drains during heavy rainfalls is also sewage because it contains pollutants that it washes off from the roads.
Any liquid waste can be called sewage.
Sewage water contains impurities mixed into it as well as some suspended pollutants.
These impurities present in the sewage are called Contaminants as they contaminate the water.
Figure 2: Sewage is a mixture of impurities
Water freshens up – An Eventful Journey
Sewers – Large and small pipes that are installed in buildings to carry sewage water are sewers.
Sewerage – A network or transport system consisting of sewers is called Sewerage.
It carries sewage water from the point where it is produced to the point where it is disposed (treatment plant).
It consists of manholes that are located at every 50 to 60 metres.
The manholes are installed at a point where two or more sewers intersect or change their directions.
Every locality has as a system that allows removal of waste from the houses and industries.
Figure 3: Sewerage
Wastewater Treatment Plant (WWTP)
Wastewater includes biological, physical and chemical matter and hence involves biological, physical and chemical processes of removal of the contaminants.
The physical and biological process of treatment of water:
1. Separation of Large Objects from Sewage Water
The wastewater is first passed through bar screens which remove big objects from the water like plastic bottles, napkins, rags, cans and sticks.
Figure 4: Bar Screens
2. Separation of Sand and Dirt
The wastewater is then sent to a grit and sand removal tank. The speed of the water is decreased at this step. This allows the sand, dirt and pebbles to settle down.
3. Removal of Solids
Now the water cycles in a tank called Clarifier which is sloped in the centre. This lets the solids like faeces to settle at the bottom. This is called Sludge.
The sludge is then separated from the water with the help of a Scrapper.
Substances like oil and grease are removed with the help of a Skimmer as they float above the water. In this step clarified water is obtained.
The sludge so obtained is passed into a tank where anaerobic bacteria can decompose it and produce biogas. The biogas is then used as a fuel.
Figure 5: Sand and Girt Removal Tank
4. Suspended Sludge Removal
The clarified water also needs to be cleaned further. Hence, it is moved to an aerator that pumps air into it.
This allows aerobic bacteria to grow in this water.
The aerobic bacteria consume organic waste, soaps, food waste and other elements that remain in the clarified water.
This water is allowed to settle for several hours and then these waste materials settle down in the tank. This is called Activated Sludge.
The water is removed from the top of this sludge with the help of machines or sand drying beds. The sludge is then dried and can be used as manure.
Figure 6: Aerator
This treated water contains fewer amounts of impurities and suspended matter. This water is safe to dump into a water body or under the ground. Hence, it is then discharged into a sea, river or underground. Nature further cleans it up.
Chemical Treatment of Wastewater:
Sometimes harmful chemicals can be present in the water even after treating them physically and biologically.
These chemicals are therefore removed by using disinfectants such as chlorine and Ozone.
Often chlorine gas or ozone gas is introduced in this water which purifies it chemically.
Figure 7: WWTP
Eucalyptus Plant and Cleaning of Water
Eucalyptus plants can absorb the water at a faster rate and then they release pure water vapour. In this way, they act as a natural water purifier. Hence, it is advised to plant Eucalyptus trees along the sewage ponds.
Figure 8: Eucalyptus Plant
Why should we adopt better housekeeping practices and become an active citizen?
We should try to reduce the waste that produced in our households so that there is not much pressure on WWTP. It is often difficult to clean tons of wastewater.
The sewage water can cause several problems such as harmful diseases, unhygienic and unsanitary conditions in the locality.
Hence, we can be more considerate about producing a limited amount of waste and we can accomplish this by adopting better housekeeping practices.
Also, we can become an active citizen by making sure that there are no open drains or sewers in our locality. If we find any we should immediately report the same to the municipality.
What better housekeeping practices we can adopt?
A good way to minimise the sewage water is to check what is going in our drains. If we dispose of our waste properly we may be able to reduce the sewage. Here are some housekeeping practices that we should adopt:
We should through all the oil and fats in dustbin rather than throwing them of the dream. Oil and fats harden and block the drains. Moreover, it is difficult to separate them from the water.
We should not throw chemicals in the drains like insecticides, pesticides or medicines. They can kill the microbes in the water that help in its purification.
We should not throw things in the drain that can block them like tea leaves, food remains, cotton, soft toys etc. We should always through them in the dustbin.
Figure 9: Treating Water at home
Sanitation and Disease
Sanitation refers to the health conditions of people related to the disposal of sewage, human excreta and provision of clean drinking water.
Poor sanitation and polluted drinking water can lead to many diseases.
Hence, a sanitation system aims to provide a clean environment for us so that we can stay away from diseases.
Improper sanitation can give rise to different diseases that arise from contaminated water such as typhoid, dysentery, hepatitis, polio, cholera and meningitis.
The human excreta is a health hazard and can lead to soil and water pollution. It can pollute the surface water and groundwater. Hence, people should never defecate in open areas.
Alternative Arrangement for Sewage Disposal
As an alternative for sewage disposal on-site sewage is being used nowadays, for example, septic tanks, compost pit toilets and chemical toilets.
The onsite sewage treatments use natural procedures to treat and dispose of the wastewater or sewage.
This system is suitable in places where there is no central wastewater collection system.
Septic Tanks – A septic tank is often installed under the ground in houses or buildings such as hospitals. It allows decomposition of sewage from home through the action of anaerobic bacteria.
Chemical Toilets – A chemical toilet has a separate compartment that treats human waste with chemicals and decreases their odour.
Composting Toilets – A composting toilet treats human waste with biological processes. The aerobic bacteria are present in a storage tank that act upon the waste and turn it into compost.
Many organizations have also installed on-site hygienic waste disposal technology in which the human excreta directly flows into a biogas plant and is then used as an energy resource.
Sanitation at Public Places
There are numerous places in our country which are very busy such as airports, railway stations and bus depots.
Many times large gatherings such as fairs and festivals are also organized where a large number of people visits.
This results in the generation of large amounts of waste and if the waste is not treated properly it can lead to several diseases and even an epidemic.
Hence we should all become aware and contribute to maintaining sanitation not only in our homes but also at public places.
If we adopt certain practices at public places we can help in maintaining their sanitation, for instance:
We should not throw garbage in public places and always use the dustbins.
22 March is celebrated as World Water Day to bring awareness among the people about the conservation of water.
2003 was called as the International year of freshwater to bring awareness among the people about the importance of water as a resource and why it is depleting at such a fast rate.
How much water is available on the earth?
Figure 1: Distribution of Water on Earth
71% of the Earth is covered with water. However, all of that cannot be consumed by the living organisms.
The figure given above represents that 97% of the earth’s water is saline that is present in the oceans and 3% of the earth’s water is fresh that is present in ice caps, glaciers and underground. This fresh water can be obtained from underground, rivers and lakes. Even then, just 1 percent of our freshwater is easily accessible, with much of it trapped in glaciers and snowfields.
Different forms of Water
Solid State – Water exists in the solid form as ice and snow on the earth.
Liquid State – Water exist in the liquid state in rivers lakes, oceans and under the ground.
Gaseous State – Water exists as water vapour in the atmosphere.
The Water Cycle
Figure 2: The Water Cycle
The water cycle is a natural process that continuously happens on earth. The water cycle maintains the amount of water on the earth. It can be divided into four phases:
Evaporation – It is a process when the water from the earth’s surface gets converted into water vapour due to the heat of the sun. The water vapour then gets into the air.
Condensation – The water vapour rises up in the atmosphere and get accumulated above, condenses and form water droplets. These droplets collect together and form clouds.
Precipitation – When the volume of droplets increases in the atmosphere, it falls on the earth as rainfall also called as Precipitation. Sometimes it also occurs as snowfall in some areas.
Collection of Water – As the water falls back on the earth, it travels along the surface and gets accumulated at different places like lakes, rivers, sea, oceans and under the ground. That’s how the amount of water is regulated on the earth.
Groundwater
Figure 3: Groundwater
The water that falls on the earth’s surface slips inside the earth and gets accumulated in the cracks and gaps of the rocks present inside the earth.
The water table is called the upper limit of the layer of water present beneath the earth. The water table can vary from one place to another.
The water that is present beneath the water table of a place is called Groundwater. This water gets accumulated inside the earth because of different sources:
Rainwater that falls on the earth slips inside the ground
Water in the rivers, lakes and Ponds often slips into the earth and get accumulated as groundwater
Infiltration – The process by which water accumulates into the ground by travelling through the soil pores is called Infiltration.
Figure 4: Infiltration
Aquifer – The underground layer of rocks that contain water present between their cracks and empty spaces is called Aquifer.
Figure 5: Aquifer and Groundwater
How underground water can be obtained?
Groundwater is generally obtained by digging Wells, using hand pumps and electric pumps.
Uses of Groundwater
Groundwater is fresh water and therefore can be used for various purposes such as:
consumption or drinking water
domestic chores
irrigation of crops
water services in public buildings and offices
firefighting
industrial purposes
Water Table Depletion
Figure 6: How Water table gets affected in different seasons
The water table of a place may decrease if we keep on taking out more water than what is getting replenished due to rainfall. There are several factors that can cause water table depletion:
1. Increasing Population
As the population of a region increases the demand of freshwater also rises sharply. This means more water is being required.
Also, increasing population demands more space which leads to the construction of more houses, shops, industries, buildings and roads.
The number of places like parks, grounds or forests decreases.
All this reduces the possibility of rainwater getting into the soil particles because the concrete floors and roads to not allow seepage of water.
This means that an increased demand and usage of groundwater as compared to the replenishment of water tables.
This results in depletion of the water table of that region.
2. Increasing Industries
Every industry requires water in its production process. As a number of industries increases, more water is drawn from the ground. All of this result in depletion of the water table.
3. Agricultural Activities
In case of no or low rainfall, farmers use groundwater to irrigate their land for agriculture. This depletes the water table over the years.
4. Deforestation
We know that plants and trees keep the soil bounded together and allow absorption of water in the soil. Uprooting them exposes the first layer of the soil which can get washed away easily. This affects the water table of that region.
5. Low Rainfall
In places where there is low or scanty rainfall the underground water table is generally low.
Distribution of Water
The distribution of water across the earth is not even due to different factors such as rainfall and climatic conditions.
Some places have a high amount of water while others face scarcity of water.
For Example, in India, places like Rajasthan get very low rainfall and hence have less water. On the other hand, places like Meghalaya receive high rainfall and have a high amount of water. Hence, there can be times when one part of India faces floods while other is suffering from a drought -like condition.
Figure 7: Rainfall in India
Water Management
No matter whether a place receives a high rainfall or low rainfall, water management is necessary to ensure that everyone gets access to an adequate amount of water.
Generally, the Civic authorities of a region are responsible for the adequate supply of water in that area.
They generally use a well-structured pipeline system to deliver water to every house and building of the locality.
Not only this it is also a responsibility of the civic authorities to prevent wastage of water and check if their supply system is adequate or not.
Along with these authorities, every individual is also responsible for saving water and preventing it from getting wasted. Hence, we should always keep a check on how we use water in our daily lives.
Water Harvesting or Rainwater Harvesting
Figure 8: Water harvesting or Rainwater harvesting
The rainwater that falls on the earth is generally allowed to flow away.
However, it can be saved and used to replenish the groundwater levels of the Earth. This process of preventing rainwater from flowing away and storing it for different purposes such as replenishing groundwater levels, household chores or industrial purposes is called rainwater harvesting.
Bawris
An ancient practice of storing water involved construction of Bawris. In old times rainwater was collected in Bawris. However, with time their usage declined. Now due to scanty rainfall people are again using them to solve the problem of water storage.
Drip Irrigation
It is an allocation technique used by farmers to water their fields.
In this, water is allowed to slowly drip into the plants so that their water directly gets into the roots of the plants.
This minimizes evaporation, saves water and allows the nutrients to reach the plants easily.
Narrow tubes are used to make water reach the roots of the plants in drip irrigation.
Figure 9: Drip irrigation
How can we save water?
We can adopt different ways to minimize the wastage of water:
Always keep the taps closed while brushing or washing the face to prevent water from flowing away unnecessarily. One should use it only when needed.
Fix any water taps that are leaking, immediately.
Instead of taking a shower use a bucket to take bath.
Use water left from washing clothes for mopping the floor and washing cars instead of running water.
Water your plans in the morning or evening times so that the water does not immediately get evaporated.
Do not waste food as it takes a lot of water to irrigate the fruits and vegetables.
Do not throw away water unnecessarily. Use water in a judicious amount
Figure 10: Outdoor Water Conservation Tips
Figure 11: Indoor Water Conservation Tips
How scarcity of water affects the plants?
The plants get dried up as they get no water and hence they can die.
There is no water to conduct photosynthesis and hence they are not able to produce any food.
They will not be able to grow upright because of scarce water.
They will no longer be able to get enough nutrients from the soil because of less or water.
As a result, there will be no food, no oxygen and hence no life without the plants.
Light is a radiation or a form of energy that our eyes can detect. Light enables us to view our surroundings. Light travels from one place to another in a straight line.
Figure 1: Light always travels in straight line
For instance, if you look at the flame of a candle with a straight pipe we can easily view the candle. However, if we bend the pipe we cannot view the candle and the light coming through it because it is blocked.
Reflection of Light
Whenever light hits an object it is either absorbed or reflected back.
Reflection of light can be defined as the phenomenon of an object throws back the light that falls on it. Hence, the reflection of light changes its path.
A mirror is generally any shiny surface that can reflect back light.
A mirror that has a plane surface is called a Plane Mirror.
A mirror that is curved, it either bulges in or out, is called a Curved Mirror.
Figure 2: Reflection of light by plane mirror
What is an image?
Figure 3: Image of Candle Formed by a Mirror
As a mirror reflects light, an image of the object that is in front of the mirror is formed on it.
The image of an object can be defined as the impression of the object created by the light on the mirror.
The distance between the image and the mirror, and the object and the mirror always remain the same.
If we increase or decrease the distance between the object and the mirror, the distance between the image and the mirror also increases or decreases, respectively.
However, the size of the image formed on the mirror can vary with respect to the distance between the object and the mirror.
If the distance between the object and the mirror increases, the size of the image decreases and vice-versa.
An image is said to be erect if the image is formed the same side up as that of the object.
The image will be called Inverted if it is formed upside-down compared to the object.
Figure 4: Inverted Image of a Candle
Left-right inversion of the image
Figure 5: Left-right inversion of the image
The image formed by the mirror is always left-right inverted. This means that the right side of the object appears as the left side of the image, and the left side of the object appears at the right side of the image.
Why the word ‘AMBULANCE’ is painted on an ambulance left-right inverted?
Figure 6: Ambulance
This is because of the left-right inversion of the image on a mirror. The word ambulance written as left-right inverted would, therefore, be read easily by the driver of the vehicle ahead of the ambulance in its rearview mirror. The rear view mirror will again invert the word left-right wise.
The Laws of Reflection of Light
Incident Ray – The light ray that falls on the reflecting surface is called an Incident Ray.
Reflected Ray –Tthe light ray that gets reflected back from a reflecting surface is called a Reflected Ray.
Normal – It is a line that is perpendicular to the reflected plane at the point of incidence of Incident Ray.
Figure 7: Incident Ray, Reflected Ray and Normal
Figure 8: The Two Laws of Reflection
Types of Reflection
Depending upon the surface of the reflecting object, the reflection of light can vary.
Diffused Reflection or Irregular Reflection: In this type of reflection, the light rays that fall on the surface are reflected back in different directions irregularly. This generally happens in the case of an irregular or roughly surfaced object.
Regular Reflection: In this type of reflection, the light rays that fall on the surface of the reflecting object reflect back in a particular direction. The reflected rays are always parallel to each other. This generally happens in case of a smooth and shiny surface.
Figure 9: Types of Reflection
Spherical Mirrors
Spherical mirror, as the name suggests, has a sphere-like shape. It appears as if it is a part of a sphere. There are two types of spherical mirrors:
Concave Mirror – It is a spherical mirror whose reflecting surface is curved inwards.
Convex Mirror – It is a spherical mirror whose reflecting surface is curved outwards.
Figure 10: Concave and Convex Mirror
The Image formed by a Concave and Convex Mirror
An image can be of two types:
Real Image
Virtual Image
The real image is formed when the light rays reflect and meet at the same point.
A virtual image is formed when light rays reflect and diverge from the same point.
It can be viewed on a screen.
It cannot be viewed on the screen.
It is always inverted.
It is always erect.
Formed by Concave mirror
Formed by Convex, Concave and Plane Mirrors
Figure 11: Formation of Real Image by Concave Mirror
Figure 12: Virtual Image by Plane Mirror
The image formed by a concave mirror has the following properties:
It can either be real or virtual.
It can either be inverted or erect.
It can have the same size as that of the object, a larger size that of the object or smaller size than that of the object.
The image formed by a convex mirror has the following properties:
It is always virtual.
It is always upright (erect).
It is smaller in size as that of the object
Applications of Concave Mirrors:
Satellite dishes use a concave mirror to gather all the signals and reflect them on a certain point.
Dentists use a concave mirror to reflect light on a particular tooth.
Shaving Mirrors are concave in shape.
Headlights of a car have a concave mirror so that we can reflect back light straight on the path.
Torches also use concave Mirrors.
Figure 13: Concave Mirror Used in Torch
Applications of Convex Mirrors
The rear view mirrors are convex mirrors as they provide a wider view of the road behind.
Security mirrors near an ATM are convex so that the user can detect easily if anyone else is watching from behind or not.
Figure 14: Convex Mirror used in a Rearview Mirror
Lenses
A lens is a part of a reflecting material like glass or plastic but curved from both sides. Lenses are unlike mirrors that have a reflecting surface only on one side. Depending upon its shape a lens can be categorized as:
Convex Lens – A Convex Lens is curved outwards. It is thicker in the centre and narrows down at the edges. It merges the light rays passing through it at a certain point. Therefore, it is also called a Converging Lens.
Concave Lens – A Concave Lens is curved inwards. It has wider edges and a thinner centre. It reflects back the light that travels through it in different directions. Therefore, it is also called a Diverging Lens.
Figure 15: Convex Lens and Concave Lens
Images formed by Convex and Concave Lenses
A Convex lens forms an image that is:
real
inverted
the image is large and appears close to the lens
A Concave lens forms an image that is:
virtual
erect
small and appears far away
Figure 16: Image formed by Convex and Concave Lense
Sunlight
What is a Rainbow?
Figure 17: Formation of Rainbow
A rainbow is a natural phenomenon in which the light rays of the sun are reflected and refracted by the water droplets present in the atmosphere.
A rainbow appears as an arc on the sky that contains a band of seven colours – Red, orange, yellow, green, blue, indigo and violet.
This also means that the white light of the sun contains seven coloured lights in it that separate out due to refraction (called a Spectrum of Lights). This spectrum of white light can be seen in the following:
Rainbows
Soap bubbles
Surface of a CD
Prisms
Figure 18: Spectrum of White Light through a Prism
Newton’s Disc
Figure 19: Newton’s Disc
The Newton’s disc can be obtained by dividing a disk into 7 partitions and painting each of them with the seven colours of the rainbow.
When the disc is rotated at a fast pace in daylight all the colours tend to mix together and the disc appears whitish in colour.
What is light?
Light is a radiation or a form of energy that our eyes can detect. Light enables us to view our surroundings. Light travels from one place to another in a straight line.
Figure 1: Light always travels in straight line
For instance, if you look at the flame of a candle with a straight pipe we can easily view the candle. However, if we bend the pipe we cannot view the candle and the light coming through it because it is blocked.
Reflection of Light
Whenever light hits an object it is either absorbed or reflected back.
Reflection of light can be defined as the phenomenon of an object throws back the light that falls on it. Hence, the reflection of light changes its path.
A mirror is generally any shiny surface that can reflect back light.
A mirror that has a plane surface is called a Plane Mirror.
A mirror that is curved, it either bulges in or out, is called a Curved Mirror.
Figure 2: Reflection of light by plane mirror
What is an image?
Figure 3: Image of Candle Formed by a Mirror
As a mirror reflects light, an image of the object that is in front of the mirror is formed on it.
The image of an object can be defined as the impression of the object created by the light on the mirror.
The distance between the image and the mirror, and the object and the mirror always remain the same.
If we increase or decrease the distance between the object and the mirror, the distance between the image and the mirror also increases or decreases, respectively.
However, the size of the image formed on the mirror can vary with respect to the distance between the object and the mirror.
If the distance between the object and the mirror increases, the size of the image decreases and vice-versa.
An image is said to be erect if the image is formed the same side up as that of the object.
The image will be called Inverted if it is formed upside-down compared to the object.
Figure 4: Inverted Image of a Candle
Left-right inversion of the image
Figure 5: Left-right inversion of the image
The image formed by the mirror is always left-right inverted. This means that the right side of the object appears as the left side of the image, and the left side of the object appears at the right side of the image.
Why the word ‘AMBULANCE’ is painted on an ambulance left-right inverted?
Figure 6: Ambulance
This is because of the left-right inversion of the image on a mirror. The word ambulance written as left-right inverted would, therefore, be read easily by the driver of the vehicle ahead of the ambulance in its rearview mirror. The rear view mirror will again invert the word left-right wise.
The Laws of Reflection of Light
Incident Ray – The light ray that falls on the reflecting surface is called an Incident Ray.
Reflected Ray –Tthe light ray that gets reflected back from a reflecting surface is called a Reflected Ray.
Normal – It is a line that is perpendicular to the reflected plane at the point of incidence of Incident Ray.
Figure 7: Incident Ray, Reflected Ray and Normal
Figure 8: The Two Laws of Reflection
Types of Reflection
Depending upon the surface of the reflecting object, the reflection of light can vary.
Diffused Reflection or Irregular Reflection: In this type of reflection, the light rays that fall on the surface are reflected back in different directions irregularly. This generally happens in the case of an irregular or roughly surfaced object.
Regular Reflection: In this type of reflection, the light rays that fall on the surface of the reflecting object reflect back in a particular direction. The reflected rays are always parallel to each other. This generally happens in case of a smooth and shiny surface.
Figure 9: Types of Reflection
Spherical Mirrors
Spherical mirror, as the name suggests, has a sphere-like shape. It appears as if it is a part of a sphere. There are two types of spherical mirrors:
Concave Mirror – It is a spherical mirror whose reflecting surface is curved inwards.
Convex Mirror – It is a spherical mirror whose reflecting surface is curved outwards.
Figure 10: Concave and Convex Mirror
The Image formed by a Concave and Convex Mirror
An image can be of two types:
Real Image
Virtual Image
The real image is formed when the light rays reflect and meet at the same point.
A virtual image is formed when light rays reflect and diverge from the same point.
It can be viewed on a screen.
It cannot be viewed on the screen.
It is always inverted.
It is always erect.
Formed by Concave mirror
Formed by Convex, Concave and Plane Mirrors
Figure 11: Formation of Real Image by Concave Mirror
Figure 12: Virtual Image by Plane Mirror
The image formed by a concave mirror has the following properties:
It can either be real or virtual.
It can either be inverted or erect.
It can have the same size as that of the object, a larger size that of the object or smaller size than that of the object.
The image formed by a convex mirror has the following properties:
It is always virtual.
It is always upright (erect).
It is smaller in size as that of the object
Applications of Concave Mirrors:
Satellite dishes use a concave mirror to gather all the signals and reflect them on a certain point.
Dentists use a concave mirror to reflect light on a particular tooth.
Shaving Mirrors are concave in shape.
Headlights of a car have a concave mirror so that we can reflect back light straight on the path.
Torches also use concave Mirrors.
Figure 13: Concave Mirror Used in Torch
Applications of Convex Mirrors
The rear view mirrors are convex mirrors as they provide a wider view of the road behind.
Security mirrors near an ATM are convex so that the user can detect easily if anyone else is watching from behind or not.
Figure 14: Convex Mirror used in a Rearview Mirror
Lenses
A lens is a part of a reflecting material like glass or plastic but curved from both sides. Lenses are unlike mirrors that have a reflecting surface only on one side. Depending upon its shape a lens can be categorized as:
Convex Lens – A Convex Lens is curved outwards. It is thicker in the centre and narrows down at the edges. It merges the light rays passing through it at a certain point. Therefore, it is also called a Converging Lens.
Concave Lens – A Concave Lens is curved inwards. It has wider edges and a thinner centre. It reflects back the light that travels through it in different directions. Therefore, it is also called a Diverging Lens.
Figure 15: Convex Lens and Concave Lens
Images formed by Convex and Concave Lenses
A Convex lens forms an image that is:
real
inverted
the image is large and appears close to the lens
A Concave lens forms an image that is:
virtual
erect
small and appears far away
Figure 16: Image formed by Convex and Concave Lense
Sunlight
What is a Rainbow?
Figure 17: Formation of Rainbow
A rainbow is a natural phenomenon in which the light rays of the sun are reflected and refracted by the water droplets present in the atmosphere.
A rainbow appears as an arc on the sky that contains a band of seven colours – Red, orange, yellow, green, blue, indigo and violet.
This also means that the white light of the sun contains seven coloured lights in it that separate out due to refraction (called a Spectrum of Lights). This spectrum of white light can be seen in the following:
Rainbows
Soap bubbles
Surface of a CD
Prisms
Figure 18: Spectrum of White Light through a Prism
Newton’s Disc
Figure 19: Newton’s Disc
The Newton’s disc can be obtained by dividing a disk into 7 partitions and painting each of them with the seven colours of the rainbow.
When the disc is rotated at a fast pace in daylight all the colours tend to mix together and the disc appears whitish in colour.
Revision Notes on Light
What is light?
Light is a radiation or a form of energy that our eyes can detect. Light enables us to view our surroundings. Light travels from one place to another in a straight line.
Figure 1: Light always travels in straight line
For instance, if you look at the flame of a candle with a straight pipe we can easily view the candle. However, if we bend the pipe we cannot view the candle and the light coming through it because it is blocked.
Reflection of Light
Whenever light hits an object it is either absorbed or reflected back.
Reflection of light can be defined as the phenomenon of an object throws back the light that falls on it. Hence, the reflection of light changes its path.
A mirror is generally any shiny surface that can reflect back light.
A mirror that has a plane surface is called a Plane Mirror.
A mirror that is curved, it either bulges in or out, is called a Curved Mirror.
Figure 2: Reflection of light by plane mirror
What is an image?
Figure 3: Image of Candle Formed by a Mirror
As a mirror reflects light, an image of the object that is in front of the mirror is formed on it.
The image of an object can be defined as the impression of the object created by the light on the mirror.
The distance between the image and the mirror, and the object and the mirror always remain the same.
If we increase or decrease the distance between the object and the mirror, the distance between the image and the mirror also increases or decreases, respectively.
However, the size of the image formed on the mirror can vary with respect to the distance between the object and the mirror.
If the distance between the object and the mirror increases, the size of the image decreases and vice-versa.
An image is said to be erect if the image is formed the same side up as that of the object.
The image will be called Inverted if it is formed upside-down compared to the object.
Figure 4: Inverted Image of a Candle
Left-right inversion of the image
Figure 5: Left-right inversion of the image
The image formed by the mirror is always left-right inverted. This means that the right side of the object appears as the left side of the image, and the left side of the object appears at the right side of the image.
Why the word ‘AMBULANCE’ is painted on an ambulance left-right inverted?
Figure 6: Ambulance
This is because of the left-right inversion of the image on a mirror. The word ambulance written as left-right inverted would, therefore, be read easily by the driver of the vehicle ahead of the ambulance in its rearview mirror. The rear view mirror will again invert the word left-right wise.
The Laws of Reflection of Light
Incident Ray – The light ray that falls on the reflecting surface is called an Incident Ray.
Reflected Ray –Tthe light ray that gets reflected back from a reflecting surface is called a Reflected Ray.
Normal – It is a line that is perpendicular to the reflected plane at the point of incidence of Incident Ray.
Figure 7: Incident Ray, Reflected Ray and Normal
Figure 8: The Two Laws of Reflection
Types of Reflection
Depending upon the surface of the reflecting object, the reflection of light can vary.
Diffused Reflection or Irregular Reflection: In this type of reflection, the light rays that fall on the surface are reflected back in different directions irregularly. This generally happens in the case of an irregular or roughly surfaced object.
Regular Reflection: In this type of reflection, the light rays that fall on the surface of the reflecting object reflect back in a particular direction. The reflected rays are always parallel to each other. This generally happens in case of a smooth and shiny surface.
Figure 9: Types of Reflection
Spherical Mirrors
Spherical mirror, as the name suggests, has a sphere-like shape. It appears as if it is a part of a sphere. There are two types of spherical mirrors:
Concave Mirror – It is a spherical mirror whose reflecting surface is curved inwards.
Convex Mirror – It is a spherical mirror whose reflecting surface is curved outwards.
Figure 10: Concave and Convex Mirror
The Image formed by a Concave and Convex Mirror
An image can be of two types:
Real Image
Virtual Image
The real image is formed when the light rays reflect and meet at the same point.
A virtual image is formed when light rays reflect and diverge from the same point.
It can be viewed on a screen.
It cannot be viewed on the screen.
It is always inverted.
It is always erect.
Formed by Concave mirror
Formed by Convex, Concave and Plane Mirrors
Figure 11: Formation of Real Image by Concave Mirror
Figure 12: Virtual Image by Plane Mirror
The image formed by a concave mirror has the following properties:
It can either be real or virtual.
It can either be inverted or erect.
It can have the same size as that of the object, a larger size that of the object or smaller size than that of the object.
The image formed by a convex mirror has the following properties:
It is always virtual.
It is always upright (erect).
It is smaller in size as that of the object
Applications of Concave Mirrors:
Satellite dishes use a concave mirror to gather all the signals and reflect them on a certain point.
Dentists use a concave mirror to reflect light on a particular tooth.
Shaving Mirrors are concave in shape.
Headlights of a car have a concave mirror so that we can reflect back light straight on the path.
Torches also use concave Mirrors.
Figure 13: Concave Mirror Used in Torch
Applications of Convex Mirrors
The rear view mirrors are convex mirrors as they provide a wider view of the road behind.
Security mirrors near an ATM are convex so that the user can detect easily if anyone else is watching from behind or not.
Figure 14: Convex Mirror used in a Rearview Mirror
Lenses
A lens is a part of a reflecting material like glass or plastic but curved from both sides. Lenses are unlike mirrors that have a reflecting surface only on one side. Depending upon its shape a lens can be categorized as:
Convex Lens – A Convex Lens is curved outwards. It is thicker in the centre and narrows down at the edges. It merges the light rays passing through it at a certain point. Therefore, it is also called a Converging Lens.
Concave Lens – A Concave Lens is curved inwards. It has wider edges and a thinner centre. It reflects back the light that travels through it in different directions. Therefore, it is also called a Diverging Lens.
Figure 15: Convex Lens and Concave Lens
Images formed by Convex and Concave Lenses
A Convex lens forms an image that is:
real
inverted
the image is large and appears close to the lens
A Concave lens forms an image that is:
virtual
erect
small and appears far away
Figure 16: Image formed by Convex and Concave Lense
Sunlight
What is a Rainbow?
Figure 17: Formation of Rainbow
A rainbow is a natural phenomenon in which the light rays of the sun are reflected and refracted by the water droplets present in the atmosphere.
A rainbow appears as an arc on the sky that contains a band of seven colours – Red, orange, yellow, green, blue, indigo and violet.
This also means that the white light of the sun contains seven coloured lights in it that separate out due to refraction (called a Spectrum of Lights). This spectrum of white light can be seen in the following:
Rainbows
Soap bubbles
Surface of a CD
Prisms
Figure 18: Spectrum of White Light through a Prism
Newton’s Disc
Figure 19: Newton’s Disc
The Newton’s disc can be obtained by dividing a disk into 7 partitions and painting each of them with the seven colours of the rainbow.
When the disc is rotated at a fast pace in daylight all the colours tend to mix together and the disc appears whitish in colour.
Electric Circuits A continuous conducting path (consisting of wires, bulb, switch, etc.) between the two terminals of a cell or battery along with an electric current flows, is known as an electric circuit. e.g. take a cell having a positive terminal (+) and a negative terminal (-). Now try to connect the positive terminal of the cell to one end of the switch with a piece of copper wire and other ends of the switch to one end of bulb holder with another piece of copper wire. The negative terminal of the cell is connected directly to the other end of the bulb holder with a wire (as shown in the figure), so this kind of setup is known as an electric circuit.
Circuit Diagram A circuit diagram tells us how the various components in an electric circuit have been connected by using the electrical symbols of the components. (i) When the bulb glows In an electric circuit when the switch is closed, then the switch is said to be in the ON position. And when the switch in a circuit is open, then the switch is said to be in the OFF position. So, in an electric circuit, a bulb lights up only when the switch is in the ON position and at that time, we can say that the electric circuit is complete because the current flows throughout the circuit instantly (as shown in the figure) electric circuit
(ii) When the bulb does not glow While checking the circuit notice that sometimes the bulb does not glow even when the switch is in the ON position. This condition can occur only if the bulb gets fused, i.e. its filament breaks. It is a difficult and time-consuming job to draw the electric circuit by making the actual drawings of cell, battery, switch, bulb, etc. So, the scientists have devised a very easy way to represent the component of an electric circuit (cell, battery, switch, bulb, etc.) with the help of symbols, which are easy to draw.
Some of the commonly used symbols for electric components are shown here:
Electric Cell and Battery The common source of electricity to run the number of devices, e.g. torches, radio, electric clocks and watches, toys, etc., is an electric cell, but sometimes a single cell is not sufficient to run many devices as they require high voltage to run all these appliances. The cell provides much less electricity as compared to that provided by the electric supply line, e.g. in the case, a single electric cell which provides only 1.5 V of electricity, whereas electricity from the power station is supplied to our home at very high voltage of 220 V.
Combination of Electric Cells Since the higher voltage can be obtained by combining a number of cells in series. So, when the positive terminal of one cell is joined with the negative terminal of the other cell, then the cells are said to be joined in series (as shown in figure given below). So, a battery can be defined as the group of cells joined together in the series, e.g. in a torch, the cells are placed one after the other. But in many devices, cells are not placed one after the other, e.g. in a TV remote control, the two cells are placed side by side (or parallel to each other) instead of single one. So, two or more cells connected in side by side manner are said to be joined in parallel. This combination is also known as battery. If we combine two cells by keeping the positive terminal of one cell in contact with the positive terminal of the other cell or negative terminal of one cell in contact with the negative terminal of the other cell, then the battery obtained will not work.
The batteries which are used in cars, buses, trucks, inverters, etc., are also made of cells. There is a special feature of car battery is that its cells can be recharged. Ordinary cells, however, cannot be recharged.
Connection of Cells/Battery ‘+’ and ‘-‘ symbols are printed in the battery in order to have an exact placement of the cells in their respective battery compartment.
The switch or key can be placed anywhere in the circuit.
The circuit is complete and it is said to be closed only when the switch is ON.
The circuit is incomplete and it is said to be open, only when the switch is OFF.
There is a thin wire in the bulb, called filament which glows when an electric current passes through it. So, if the bulb gets fused, then its filament gets broken. Note: Never touch a lighted electric bulb connected to the mains as it may be very hot and can damage your hands.
Heating Effect of Electric Current Production of heat in an electric device due to the flow of electric current is called the heating effect of electric current. We have seen an electric heater used for cooking, an electric bulb or room heater. So, when these appliances are switched ON after connecting to the electric supply, then their elements become red hot and release the heat. This happens due to the heating effect of electric current.
The degree to which a material opposes the passage of current through itself is known as its resistance. Actually, when an electric current passes through a high resistance wire, the electric energy gets converted into heat energy and this heat energy heats up the wire.
Element All electrical heating devices consist of a coil of wire called an element. When these appliances are switched ON after connecting to the electric supply, then their elements become red hot and release the heat. There are some electric appliances such as immersion heaters, hotplates, irons, geysers, electric kettles, hair dryers, etc., which have elements inside them.
Factors on Which the Heating Effect of Current Depends There are two factors on which the heating effect of current depends: (i) Resistance of wire: Greater the resistance of a wire, greater will be the heat produced in it by a given current, e.g. if we choose two wires, one of copper and other is nichrome of equal length and equal thickness and pass them the equal amount of current through them for the same duration, then we will notice that nichrome wire will become hotter in comparison to the copper wire. It is due to the reason that the resistance of nichrome wire is more than that of the copper wire. That is why the nichrome wire is used to make heating elements of electric heating appliances such as electric room heater, electric iron, etc. The resistance of a wire depends on the material of the wire, length of wire and thickness of the wire.
.
Applications of the Heating Effect of Current Some of the important applications of heating effect of electric current are
For the production of light, the heating effect of electric current is utilised in the electric bulbs.
For the working of electrical heating appliances such as water heater, electric room heater, electric iron, etc., the heating effect of electric current is utilised.
The heating effect of electric current is utilised in a safety device called ‘electric fuse’.
Compact Fluorescent Lamps (CFLs) An electric bulb is basically used for producing light but it also releases the heat which is not desirable because a major part of the electricity consumed by the filament of a bulb is converted into heat and results in the wastage of electricity. So, this wastage can be decreased by using fluorescent tube light or CFLs (as shown in the figure) in place of the bulbs. However, before purchasing bulbs, tubes orCFL’s we should look for the ISI marl? (ISI- Bureau of Indian standard). It is because the ISI mark ensures that the appliance is safe and wastage of energy is minimum.
Electric Fuse A safety device which works on the heating effect of current and prevents electric fires or damage to electrical appliances due to excessive flow of current is known as the fuse. This safety device consists of a short length of a thin wire of tin plated copper having a low melting point and this wire has a much greater resistance than the rest of the electric wiring in the house.
So, due to this, if the current in the electric wiring suddenly increases too much, then the fuse wire gets heated, then it melts and breaks the circuit which means that the current flowing in the household circuit will stop. This prevents fire in the house and also the damage of various electrical appliances like refrigerator, fans, tube lights, TV, etc. When a fuse gets blown (breaks), a new fuse has to be fitted in its place in order to restore the electricity supply in the household circuit. Note: We should not use a thick wire as a fuse wire because it will have low resistance and thus it will not get heated to its melting point ‘ when a large current passes through it.
Cause of Large Current Flow in Household Electric Wiring An extremely large current can flow in the household electric wiring circuits under two circumstances overloading and short circuit. We might have read reports in the newspaper about fires caused by short circuits and overloading. Now, let’s study these two terms.
Overloading It is a situation when too many electrical appliances are connected to a single socket, they draw an extremely large amount of current from the household circuit. The flow of large current due to overloading may heat the copper wires of household wiring to a very high temperature and fire may be started.
Short Circuit Electric current is supplied by household through two insulated wires which run together and reach each and every electrical appliances. One insulated wire is called live wire and the other insulated wire is called neutral wire and both these wires are necessary for the working of an electrical appliance (say an electric iron).
So, if in case the plastic insulation of the live wire and the neutral wire gets worn due to wear and tear, then the two naked wires touch each other. So, this touching of live wire and neutral wire directly is known as a short circuit. Due to which a large current flows through the household wiring and this large’ current may heat the wires to a dangerously high temperature and a fire may be started. Note: Always use proper fuses which have been specified for particular applications carrying ISI mark Never use just any wire or strip of metal in place of a fuse.
Miniature Circuit Breakers (MCBs) This ore increasingly being used these days in place of fuses. MCB does not work on the heating effect of current as it works on the magnetic effect of current. These switches outomaticoUy turn OFF when the current in a circuit exceeds the safe limit. We turn them ON and the circuit ¡s once again completed.
Magnetic Effect of Electric Current If the electric current passes through a wire, then the current carrying wire behaves like a magnet. This phenomenon is known as the magnetic effect of current. It was discovered by a scientist Hans Christian Oersted who found that when an electric current is passed in a wire, then the compass needle placed near it got deflected from its usual North-South position.
A straight wire carrying an electric current produces a magnetic effect. The magnetic effect is increased only if we use a long coil of wire instead of a straight wire. Even further the magnetic effect is increased if the coil of wire is wound around an iron rod and then current is passed through it.
Electromagnets It is a magnet made by using electric current. An electromagnet works on the magnetic effect of current. An electromagnet consists of a coil of insulated wire wrapped around a piece of iron which is magnetised only when an electric current is passed through the coil. This magnet consists of a long coil of insulated copper wire wound around an iron rod and when the two ends of the coil get connected to a cell, then a current passes through the coil and produces a magnetic effect. The magnetic effect magnetises the iron rod. In this way, the iron rod becomes an electromagnet. The magnetism of an electromagnet remains as long as the current is flowing in its coil. So, if we switch OFF the current in the coil, then all the magnetism of the iron rod disappear and it will no longer behave like a magnet. There are two factors through which an electromagnet can be made stronger, i.e.
By increasing the amount of current used in the coil.
By increasing the number of turns forming the coil.
Uses of Electromagnets
These magnets are used in electrical appliances such as an electric bell, electric fan, electric motor.
These magnets have their utilisation in electric generators where the very strong magnetic field is required.
For deflecting electron beam of the picture tube of TV electromagnets are used.
For the magnetic separation of iron ores from the earthly substances, electromagnets are used.
For preparing strong permanent magnets, electromagnets are used.
Advantages of Electromagnets over Permanent Magnets An electromagnet is a temporary form of the magnet because its magnetism is only for the duration of current flowing in its coil. Actually, an electromagnet is better than a permanent magnet in many respects. There are some of the advantages of the electromagnets over the permanent magnets which are stated as follows:
The magnetism of an electromagnet can be switched ON or switched OFF as desired. While it is not possible with a permanent magnet.
By increasing the number of turns in the coil and by increasing the current passing through the coil an electromagnet can be made very strong. On the other hand, a permanent magnet cannot be made so strong.
Electric Bell An electric bell works on the magnetic effect of current. It has an electromagnet in it. Let us study its construction and working as well.
Construction of Electric Bell The electric bell has a U-shaped electromagnet. There is a small iron bar called armature which is h^d in front of the poles of the electromagnet. The lower end of the iron bar is attached to a flat spring and the flat spring is itself fixed to a metal bracket. The upper end of the iron bar has a clapper attach to it. A metal gong is fixed near the clapper.
Working of Electric Bell In order to ring the bell, first of all, we press the push button switch in order to ring the bell. So, when we press the switch, then the electric circuit of the bell is completed and a current passes through the coil of the electromagnet and it gets magnetised. The electromagnet attracts the iron armature towards itself.
So, as the armature moves towards the poles of the electromagnet, the clapper attached to it strikes the gong and produces a ringing sound. It implies that the bell rings. When the armature moves towards the magnet, its contact with the contact screw is broken. Due to this, the electric circuit breaks and no current flows in the electromagnet coil. The electromagnet loses its magnetism for a moment and the armature is no longer attracted by it. The flat spring brings back the iron armature to its original position and the clapper also moves away from the gong.
As soon as the armature comes back and touches the contact screw the circuit is completed and current starts flowing in the electromagnet coil again. The electromagnet attracts the iron armature once again and the clapper strikes the gong again producing a ringing sound.
So, this process of ‘make and break’ of the electric circuit continues as long as we are pressing the switch. Due to this, the armature vibrates forwards and backwards rapidly each time making the clapper strike the gong. Thus, the clapper strikes the gong rapidly producing an almost continuous sound.
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If an object keeps on changing its position with time, it is said to be moving or in motion. Motion can be of different types:
Linear or straight in which the object travels in a straight line.
Circular in which the object travels along a circular path.
Curvilinear in which the object moves along a curve.
Figure 1: Examples of Motion
Slow and Fast Motion
If one object covers a particular distance in less time and another object covers the same distance in more time then the first object is said to be moving slowly while the second object is said to be moving faster.
The Speed of an object
The distance travelled by an object in unit time is called its Speed.
Types of Speed:
Uniform Speed – When the object travels a fixed distance same time gaps, it is said to have a uniform speed.
Non-uniform speed – When an object covers different distances in different time gaps, it is said to have a non-uniform speed.
Average speed – The total distance travelled by an object divided by the total time taken by the object is called its average speed
Figure 2: Finding Speed, Time and Distance
Measuring Time
There are many events in nature that repeat after a time interval:
Morning – The rising of the sun
Day and Night – The time between the sunrise and sunset
Month – The time between two new moons
Year – The time the earth takes to complete its one revolution around the sun
Time measuring devices or clocks – Clocks use the concept of periodic motion to measure time. It means that it uses motion that repeats itself in equal amounts of time. There are different types of time measuring devices.
Sundial – It uses the position of the sun to depict time
Sand Clock (hourglass) – It uses sand to measure time
Water Clock – It uses water to measure time
Pendulum Clock – It uses a pendulum to measure time
Quartz Clocks – They have an electric circuit that works with the help of cells. They provide accurate time.
Periodic Motion of a Simple Pendulum
Figure 8: Simple Pendulum
A simple pendulum contains a Bob. It is a metallic ball or a stone which is suspended from a rigid stand with the help of a thread.
Oscillatory motion – The to and fro motion of the pendulum is called as Oscillatory Motion. The bob of the pendulum does move from the centre (mean position) of the pendulum to its extreme positions on the other side.
Oscillation – When the bob moves from its centre (mean position) to its extreme ends it is said to complete one oscillation.
Time Period of a pendulum – The time taken by the pendulum bob to complete one oscillation is called its Time Period.
Speedometer – It is a device which is used in vehicles such as cars and trucks which measures the speed in kilometer per hour.
Odometer – It is a device which measures the distance travelled by a vehicle in meters or kilometers.
Figure 10: Measure of Distance and Speed of a car
Distance-time Graph
A graph which represents the distance travelled by an object with respect to time is called a distance-time graph.
Making a distance-time graph:
1. Mark the x-axis and y-axis and divide them in equal quantities.
Figure 11: Take the first quadrant
2. Choose one scale to represent distance (for example, x-axis to represent distance where 1 km = 1 cm) and the other to represent time (for example, y-axis to represent the time where 1 min = 1 cm).
Figure 12: Choosing the scale
3. Mark the values of time and distance in the graph. 4. Mark the set of values of time taken and distance covered in that time by the object in the graph. For example, if 1 km is covered in 1 minute then mark 1 unit on both the x-axis and y-axis.
Figure 13: Marking the values for time and distance
5. Now draw lines parallel to x-axis and y-axis at the points that you have marked. 6. Mark the points where these lines intersect on the graph. These points show the position of the moving object. 7. Now join all the points of intersection and obtain a straight-line graph. 8. This is the distance-time graph of a moving object.
Figure 14: Obtaining a straight line graph
The shape of the distance-time graph can be the following:
Shape of Graph
Interpretation
Straight line
The object has a uniform or constant speed
Parallel to time-axis
It is a stationary object
Curve shape
The object has a non-uniform speed
Figure 15 Distance-time Graphs
To find the speed of the distance-time graph
Speed = distance/time = (final position of object – initial position of object)/time taken by object
Also, the speed of the distance-time graph can be calculated by the Slope of a graph. The steeper the slope of the graph, the more is the speed of the object. For example, in the graph given below object A has a steeper slope. This means that object A is moving at a higher speed than object B.
Figure 11: Take the first quadrant
Figure 12: Choosing the scale
Figure 13: Marking the values for time and distance
Figure 14: Obtaining a straight line graph
