CLASS 7TH | PHYSICS | ELECTRICITY AND MAGNETISM | REVISION NOTES

Magnetism:

It the force of attraction or repulsion that act at a distance because of presence of magnetic
field.
Magnetic field is caused or generated by moving electrically charged particles or it is inherent
in magnetic objects such as magnet.
Magnets:
• A magnet has two ends termed as poles. North Pole and South Pole.
• Like poles repel, Opposite poles attracts
• Every magnet creates invisible area around it , called as Magnetic field
• Earth itself act as giant magnet, North pole of magnet indicates north pole of earth
• If you cut the bar magnet at center , you get another two bar magnets
• Magnetization can be brings about in non-magnetic material such as iron nail by
simply running a magnet over it.
Magnetic Field:
The magnetic field is nothing but imaginary area around a magnet in which there
is magnetic force.
It is invisible magnetic field that describes the magnetic influence that extends all around
them.
Electromagnet:

Electromagnet are those temporary magnets in which , the strength of their magnetic field
can easily be controlled just by changing the amount of electric current that flows through it.

Laws of Magnetism:

1. Like poles repel each other whereas unlike pole attracts each other
2. Poles are opposite to each other but equal in magnitude or strength
3. Poles are inseparable, means on cutting of bar magnet new magnets are formed with
   new poles.
4. Long bar magnet can retained magnetism longer than short bar magnets due to the
   less demagnetizing action of poles. (Horse-shoe magnet retained more than bar
   magnet)
5. On Magnet demagnetization as well as remagnetization can be performed. Short Notes
   Class 7 IGS
6. Application of magnets and electromagnets:
7. • Electromagnets are used in numerous of electrical devices such as electrical bell,
8. telephone, radio, transistor, loudspeaker etc.
9. • It is also used in fan, motor, mixers as well as room cooler.
10. • Used in compass needle
11. • Common use big electromagnets are used for removing iron objects from scrap.
12. The branch of physics which deals with the relationship between electricity and magnetism
13. termed as “Electromagnetism”
14. Electrical bell :
15. It is made of an electromagnet and work on its application where there is presence of bell
16. (metal shaped cup like structure), soft iron strip which act as a hammer and contact screw.
17. The shape of device is somewhat cup-shaped, ultimately made up of metal.
18. A soft iron strip works as a small hammer.
19. Working :
20. • Whenever the switched is on then the current is passed through the circuit and the
21. electromagnet acts like a temporary magnet and start attracting the iron strip.
22. • The iron strip that is hammer, which is elastic in nature, strikes the bell.
23. • At the same moment, its contact with the screw is lost , which turn out to be the
24. breaking of circuit and the current stops flowing through the electromagnet.
25. • In fraction of seconds of interval, the iron strip returns to its original position, and
26. quickly the current passes through the electromagnet.
27. This repeated process happens many times in a second, and as the hammer strikes the bell,
28. the sound is heard clearly.
29. The bell rings till the circuit has been switched off temporarily.
30. The electric bell is used in alarms and bells is schools, offices, homes and industries.
31. Electrical current:
32. It is defined as the amount of charge flowing per second through a cross sectional part of
33. conductor.
34. SI unit is Ampere (A).
35. In a conductor the passage of electric current is only due to the flow of electrons as atoms
36. sticks to their position.

Potential Difference:

It is the difference in the amount of energy which tend to act like carriers of charge between
two points in a circuit.
It is required for maintaining the flow of charges in the conductor
It is measured by “Voltmeter” The SI unit for electrical potential is volt (v).
o Combination of two or more cells is consider as battery
o In the circuit diagram the zigzag line indicate the Resistor which is generally made
from metallic alloys namely nichrome , eureka , tungsten , manganin etc.
Electrical Circuit Diagram:
A circuit diagram also known as elementary diagram or may be sometimes as electronic
schematic is nothing but the graphical or symbolic representation of an electrical circuit on
paper.
It is easier to use a circuit diagram rather than show the actual circuit elements.
Following conditions are maintained to ensure current is flowing from circuit:

1. A closed path for flow of current
2. Cell or battery that responsible for production of desire potential difference
   Conductors are those material such as iron, copper, graphite which easily allow flow of
   charges through them.
   Insulators are those such as dry wood, glass, rubber , do not allow flow of charges through
   them.
   • Series circuit:
   In a series circuit, all components such as resistor, voltmeter , battery are connected as
   name suggest that is in series or end-to-end, resulting in a single path for current flow.
   In this case the resistance is increases as the number of appliances connected.
   • Parallel circuit:
   In a parallel circuit, as name suggests all components are connected across each other.
   Which result in the formation of exactly two different sets of electrically common points.
   In this having additional components does not increase resistance unlike the series.
   The malfunctioning in one device in reality does not affect the working of other devices.
   

A battery is a source of energy which provides a push that is a voltage of energy to maintain
the flow of current in the circuit.
When two cells are kept side by side then there is special arrangement to connect the
positive and negative terminal of cell.
The right way to do so , as there is flow of current from neighboring cells , the positive end of
one cell should be connected to negative end of another cell.
Considering many cells are in arrangement of one by one then , they should be connected
direct contact that is one cell follow by other with respect to maintaining positive terminal
attach to negative terminal of consecutive cell.
And in box shaped battery compartment when they place side by side parallel way then the
common metal strip should run over all negative terminals be in touch to ensure the
condition for passage of current and for same as that of positive terminal