CHAPTER 8 : NCERT SOLUTION CLASS 11TH PRACTICAL WORK IN GEOGRAPHY | EDUGROWN NOTES

Short Answer Type Questions:

Q1.How is weather forecasting useful for different groups?
Answer:
Weather forecasting is very important for all groups:

• Weather forecasts help in taking safety measures in advance in case of the likelihood of bad weather.
• It reduces the likely loss from natural calamities. Had tsunami been predicted in advance, the loss that happened could be minimized to a great extent.
• Predicting weather a few days in advance may prove very useful to farmers and to the crew of ships, pilots, fishermen, defence personnel, etc.

Q2.Explain in short about Wind Vane.
Answer:
Purpose: Wind vane is a device used to measure the direction of the wind. Structure: The wind vane is a light-weight revolving plate with an arrowhead on one end and two metal plates attached to the other end at the same angle. This revolving plate is mounted on a rod in such a manner that it is free to rotate on a horizontal plane. It responds even to a slight blow of wind.
Important Aspect: The arrow always points towards the direction from which the wind blows.

Q3.Explain in short about Anemometer.
Answer:

An anemometer is an instrument that measures wind speed and wind pressure. Anemometers are important tools for meteorologists, who study weather patterns. They are also important to the work of physicists, who study the way air moves. The most common type of anemometer has three or four cups attached to horizontal arms. The arms are attached to a vertical rod. As the wind blows, the cups rotate, making the rod spin. The stronger the wind blows, the faster the rod spins. The anemometer counts the number of rotations, or turns, which is used to calculate wind speed. Because wind speeds are not consistent—there are gusts and lulls-wind speed is usually averaged over a short period of time.

A similar type of anemometer counts the revolutions made by windmill-style blades. The rod of windmill anemometers rotates horizontally. Other anemometers calculate wind speed in different ways. A hot-wire anemometer takes advantage of the fact that air cools a heated object when it flows over it.

Q4.How do Weather observatories work in India?
Answer:
Each day weather maps are prepared for that day by the Meteorological Department from the data obtained from observations made at various weather stations across the world. In India, weather-related information is collected and published under the auspices of the Indian Meteorological Department, New Delhi, which is also responsible for weather forecasting.

The Indian Meteorological Department (IMD) was established in 1875, with its headquarters at Calcutta. The IMD headquarters are presently located at New Delhi.

Q5.Write a short note on Stevenson Screen.
Answer:
The Stevenson screen is designed to protect thermometers from precipitation and direct sunlight while allowing air to circulate freely around them. Formation: It is made from wood with louvered sides to allow free and even flow of air. It is painted white to reflect radiation. It stands on four legs and is about 3 feet 6 inches above the level of the ground. The legs must be sufficiently rigid and be buried sufficiently in the ground to prevent shaking.

The front panel is hinged at the bottom to form a door, which allows for maintenance and reading of the thermometers. The door of Stevenson screen is always towards the north in the northern hemisphere and towards the south in the southern hemisphere because direct sunrays also affect mercury.

Objective: The purpose of the Stevenson screen is to create a uniform temperature enclosure that closely represents the same temperature as the air outside.

Q6.What is aneroid barometer? How does it work?
Answer:
Aneroid barometer gets its name from the Greek word, aneros in which ‘a’ means ‘not’, ‘neros’ means ‘moisture’, hence aneroid means without liquid. It is a compact and portable instrument. It consists of a corrugated metal box made up of a thin alloy, sealed completely and made airtight after partial exhaustion of air.

It has a thin flexible lid, which is sensitive to changes of pressure. As the pressure increases, the lid is pressed inward, and this, in turn, moves a system of levers connected to a pointer, which moves clockwise over the graduated dial and gives higher reading. When the pressure decreases, the lid is pushed outward and the pointer moves counter clockwise, indicating lower pressure. Barograph works on the principle of aneroid barometer.

There are a number of vacuum boxes placed one above the other so that the displacement is large. A system of levers magnifies this movement which is recorded by a pen on a paper attached to a rotating drum. The readings of a barograph are not always accurate, and therefore, they are standardised by comparing them with a mercury barometer reading.

Q7.Explain about surface observatory in detail.
Answer:
A typical surface observatory has instruments for measuring and recording weather elements like temperature (maximum and minimum), air pressure,humidity, clouds, wind and rainfall. Information: Specialised observatories record elements like radiation, ozone atmospheric trace gases, pollution and atmospheric electricity. These observations are taken all over the globe at fixed times of the day as decided by the WMO and the use of instruments are made conforming to international standards, thus making observations globally compatible.

Different types of surface observatories in India: In India, meteorological observations are normally classified into five categories depending upon their instruments and the number of daily observations taken. The highest category is Class-I. Typical instrumental facility available in a Class-I observatory consists of the following: Maximum and minimum thermometers, Anemometer, and wind vane, Dry and Wet bulb thermometer, Rain gauge and Barometer.

Q8.Differentiate between:

(i) Wet bulb and dry bulb,
Answer:
The dry bulb and wet bulb thermometers are two identical thermometers fixed to a wooden frame. But they are different in following way:

Dry Bulb Thermometer	Wet Bulb Thermometer
It is used to measure lowest humidity	It is used to measure highest humidity.
The bulb of the dry bulb thermometer is kept uncovered and is exposed to the air	The bulb of the wet bulb thermometer is wrapped up with a piece of wet muslin, which is kept continuously moist by dipping a strand of it into a small vessel of distilled water.
Its temperature remains high.	The evaporation from the wet bulb lowers its temperature.

(ii) Aneroid Barometer and Mercury Barometer.
Answer:

Aneroid Barometer	Mercury Barometer
Aneroid barometer gets its name from the Greek word, aneros in which ‘a’ means ‘not’, ‘neros’ means ‘moisture’, hence aneroid means without liquid. It is a compact and portable instrument.	Mercury barometer is an accurate instrument and is used as a standard. In it the atmospheric pressure of any place is balanced against the weight of a column of mercury in an inverted glass tube.
It is filled with alcohol	It is filled with mercury
It is used to measure lowest temperature.	It is used to measure highest temperature.

(iii) Centigrade and the Fahrenheit.
Answer:
Both are units of measuring temperature but they have some differences.

Centigrade	Fahrenheit
On the Centigrade thermometer, the temperature of melting ice is marked 0°C and that of boiling water as 100°C, and the interval between the two is divided into 100 equal parts.	On the Fahrenheit thermometer, the freezing and boiling points of water are graduated as 32°F and 212°F respectively.
Centigrade = (Fahrenheit -32)	Fahrenheit= Centigrade ×95 +32

Long Answer Type Questions:

Q1.How is information about weather and related facts collected organized and dispensed in India?
Answer:

In India, weather-related information is collected and published under the auspices of the Indian Meteorological Department, New Delhi, which is also responsible for weather forecasting.

A typical surface observatory has instruments for measuring and recording weather elements like temperature (maximum and minimum), air pressure, humidity, clouds, wind and rainfall. Specialised observatories also record elements like radiation, ozone atmospheric trace gases, pollution and atmospheric electricity. These observations are taken all over the globe at fixed times of the day as decided by the WMO and the use of instruments are made conforming to international standards, thus making observations globally compatible. In India, meteorological observations are normally classified into five categories depending upon their instruments and the number of daily observations taken. The highest category is Class-I.

Typical instrumental facility available in a Class-I observatory consists of the following:

• Maximum and minimum thermometers
• Anemometer and wind vane
• Dry and Wet bulb thermometer
• Rain gauge
• Barometer

Observations are taken in these observatories normally at 00,03,06,09, 12,15,18,21 hours (Greenwich Mean Time) around the globe. However, for logistic reasons, some of the observatories take limited number of daily observations upper air observation during daytime only.

Weather satellites make comprehensive and large-scale observations of different meteorological elements at the ground level as well in the upper layers of the atmosphere. The geo-stationary satellites provide space-based observations about weather conditions. The Indian National Satellite (INSAT) provides valuable observations of temperature, cloud cover, wind and associated weather phenomena.

Q2.Explain the working of a barometer.
Answer:
The instrument used to measure atmospheric pressure is called a barometer. The unit of measurement is in the millibar. The most commonly used barometers are the mercury barometer, aneroid barometer and barographs. All the three work differently. Their working is explained below briefly:

1. Mercury barometer: It is an accurate instrument and is used as a standard. In it the atmospheric pressure of any place is balanced against the weight of a column of mercury in an inverted glass tube.

2.Aneroid barometer: It is a compact and portable instrument. It consists of a corrugated metal box made up of a thin alloy, sealed completely and made airtight after partial exhaustion of air. It has a thin flexible lid, which is sensitive to changes of pressure. As the pressure increases, the lid is pressed inward, and this, in turn, moves a system of levers connected to a pointer, which moves clockwise over the graduated dial and gives higher reading. When the pressure decreases, the lid is pushed outward and the pointer moves counter clockwise, indicating lower pressure.

3. Barograph: It works on the principle of aneroid barometer. There are a number of vacuum boxes placed one above the other so that the displacement is large. A system of levers magnifies this movement which is recorded by a pen on a paper attached to a rotating drum. The readings of a barograph are not
always accurate, and therefore, they are standardised by comparing them with a mercury barometer reading.

Q3.Write short notes on the following:
(i) Safe place for a thermometer
(ii) Indian Daily Weather report
Answer:
(i) Safe place for thermometer: It is not safe to keep a thermometer in sunlight. We should also not keep it in airtight surroundings. The Stevenson screen is designed to protect thermometers from precipitation and direct sunlight while allowing air to circulate freely around them. It is made from wood with louvered sides to allow free and even flow of air. It is painted white to reflect radiation. The purpose of the Stevenson screen is to create a uniform temperature enclosure that closely represents the same temperature as the air outside.

It stands on four legs and is about 3 feet 6 inches above the level of the ground. The legs must be sufficiently rigid and be buried sufficiently in the ground to prevent shaking. The front panel is hinged at the bottom to form a door, which allows for maintenance and reading of the thermometers. The door of Stevenson screen is always towards the north in the northern hemisphere and towards the south in the southern hemisphere because direct sunrays also affect mercury.

(ii) Indian Daily Weather Report: IMD became a member of the World Meteorological Organization after independence on 27 April 1949. The agency has gained in prominence due to the significance of the monsoon rains on Indian agriculture. It plays a vital role in preparing the annual monsoon forecast, as well as in tracking the progress of the monsoon across India every season.

IMD undertakes observations, communications, forecasting and weather services. In collaboration with the Indian Space Research Organisation, the IMD also uses the IRS series and the Indian National Satellite System (INSAT) for weather monitoring of the Indian subcontinent. IMD was the first weather bureau of a developing country to develop and maintain its own satellite system. IMD is one of the 6 worldwide Regional Specialized Meteorological Centers of the Tropical Cyclone Programme of the World Weather Watch of the World Meteorological Organization. It is regional nodal agency for forecasting, naming and disseminating warnings about tropical cyclone in the Indian Ocean north of the Equator.

Q4.Explain the history of weather forecasting in India.
Answer:
In 1686, Edmond Halley published his treatise on the Indian summer monsoon, which he attributed to a seasonal reversal of winds due to the differential heating of the Asian land mass and the Indian Ocean. The first meteorological observatories were established in India by the British East India Company. These included the Calcutta Observatory in 1785, the Madras Observatory in 1796 and the Colaba Observatory in 1826. Several other observatories were established in India during the first half of the 19th century by various provincial governments.

After a tropical cyclone hit Calcutta in 1864, and the subsequent famines in 1866 and 1871 due to the failure of the monsoons, it was decided to organise the collection and analysis of meteorological observations under one roof.
As a result, the Indian Meteorology Department was established in 1875. Henry Francis Blanford was appointed the first Meteorological Reporter of the IMD. In May 1889,Sir John Eliot was appointed the first Director General of Observatories in the erstwhile capital, Calcutta. The IMD headquarters were later shifted to Shimla in 1905, then to Pune in 1928 and finally to New Delhi in 1944.

Q5.Explain the instruments used to measure atmospheric pressure.
Answer:
A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. A simple barometer consists of a long glass tube (closed at one end, open at the other) filled with mercury and turned upside down into a container of mercury. The barometer works by balancing the mercury in the glass tube against the outside air pressure, just like a set of scales. As air pressure increases—that is, as the air becomes heavier—it pushes more of the mercury up into the tube. As air pressure decreases, more of the mercury drains from the tube. So the level of mercury in the tube provides a precise measure of air pressure.

Mercury barometer is . an accurate instrument and is used as a standard. In it the atmospheric pressure of any place is balanced against the weight of a column of mercury in an inverted glass tube. Aneroid barometer is a compact and portable instrument. It consists of a corrugated metal box made up of a thin alloy, sealed completely and made airtight after partial exhaustion of air. It has a thin flexible lid, which is sensitive to changes of pressure. As the pressure increases, the lid is pressed inward, and this, in turn, moves a system of levers connected to a pointer, which moves clockwise over the graduated dial and gives higher reading.

When the pressure decreases, the lid is pushed outward and the pointer moves counterclockwise, indicating lower pressure. Barograph works on the principle of aneroid barometer. There are a number of vacuum boxes placed one above the other so that the displacement is large. A system of levers magnifies this movement which is recorded by a pen on a paper attached to a rotating drum. The readings of a barograph are not always accurate, and therefore, they are standardised by comparing them with a mercury barometer reading.