Think this will be helpful for learning Physics of class VIII

2. CHAPTER 9: Electric Circuits And Current Electricity

3. LEARNING OUTCOME
1. What is resistance?
2. What do you mean by 10 ῼ?
3.What purposes we can use the resistance?
4. What types of material is used to make resistance?
5. What is unidirectional current?
6. What are the sources of unidirectional current?
7. What is alternating current?

4. 8. What are the sources of alternative current?
9. How we can effective use of electricity and to stop its wastage?
10. What is current of electron /Electricity?
11. Draw an electric Simple circuit.
12. What is potential difference?
13. What is the unit of potential difference?
14. How many types of current flow?
15. What is Ac and Dc?

5. CURRENT /ELECTRICITY
The flow of electron in a particular wire is called current or
electricity. Current is denoted by I.
The flow of electric current is basically the flow of electrons.
The unit of current: The unit of current is ampere and is denoted by A

6. SIMPLE CIRCUIT AND FLOW OF
ELECTRICITY
Q. Draw an electric Simple circuit.

7. CONVENTIONAL DIRECTIONAL OF CURRENT &
ELECTRON
When such a metal wire connected between two points,
having a potential difference, then electrons which have
negative charge, flow from the low voltage region to high
voltage region.
The current will flow as long as there is a voltage difference
between the points.

8. The flow of 1 coulomb charge through a conductor per second is called
Ampere. The unit of charge is C (coulomb).
POTENTIAL DIFFERENCE
The amount of electrical work that has to be done to carry one unit of
charge from one point to another in an electric field is called the potential
difference between the points.
If there is no potential difference two ends of a resistor, no current will
flow and no work will be done.
 Unit of potential difference is volt & denoted by V.

9. DIFFERENTTYPES OF CURRENT
There are two kinds of current flow.
(a) Unidirectional current.
(b) Alternating current.
Non periodic or unidirectional current: If there is no change in the
direction of the flow of current with time, it is called unidirectional or
direct current.
We get unidirectional current from an electric cell or battery, DC
generator.

10. Alternating current: When the flow of current changes its direction
periodically, it is called alternating current.
At present, alternating current (AC) is used all over the world. Ex- Nuclear
power plant, generator

11. RESISTANCE
The property of creating obstacle to the flow of electron of a wire is called
resistance. It is denoted by R. The unit of resistance in SI unit is Ohm.
Electrons move from the low potential to high potential .But during this
journey the electrons come into collusion with the ions in the metallic
conductor and create resistance.

13. OHM'S LAW.
At a fixed temperature the current flowing through a particular wire
or conductor is proportional to the voltage difference between the
two ends of the conductor.
This law indicate the relationship between voltage and current for a
conductor of definite composition, shape by George Simon Ohm(1789-
1854).This is known as ohm's law.

14. OHM’S LAW


15. GRAPHICAL REPRESENTATION OF OHM’S
LAW.
1. In fact the resistance of a conductor is equal to the potential
difference divided by the current in ampere.
2. From Ohm's law, we can see that if the voltage between the two ends
of a conductor is high, the current flowing the conductor will be large
and if the voltage is low, the current will be low.

16. TYPES OF CIRCUIT
Circuit
Series circuit
Parallel circuit
https://phet.colorado.edu/sims/html/circuit-construction-kit-
dc-virtual-lab/latest/circuit-construction-kit-dc-virtual-
lab_all.html

17. SERIES CIRCUIT
Series circuit is like that where electrical components are connected
one after another.

18. PARALLEL CIRCUIT
Parallel circuit:The circuit in which electric components are arranged
in such a way that one terminal of all the components are joined at a
common point and the other terminal are joined at another common
point then this circuit is called a parallel circuit.

20. AMMETER
Ammeter is an electrical
instrument With the
apparatus we can directly
measure the current in a
circuit.
Ammeter can be connected in
both circuits: Series and parallel
Ammeter is connected to any
circuit in series.

21. Voltmeter is an electrical
instrument With the apparatus
we can directly measure the
voltage in a circuit.
Voltmeter can be connected in
both circuits: Series and
parallel
Voltmeter is connected to any
circuit in parallel.
Voltmeter

23. Galvanometer
A galvanometer is one of the
instruments for measuring
electrical current par excellence.
This device is used on electrical
circuits to know and measure the
intensity and direction of
electrical current.
Ammeter is connected to any
circuit in series.

25. FUSE
To avoid such accidents some special arrangements are made.
The special arrangement is the use of fuse.
Fuse is usually made of thin wire of an alloy of tin and lead.
Fuse is connected to any circuit in series.
A ten ampere fuse means:
No current above 10 ampere can pass through
it because it will then melt and make the circuit
off.
1. For electric lamps, fans, televisions etc : 5 A
2. For electric kettle or calendar : 15 A
3.The main fuse of the house may be 30 or 60
ampere

27. The Effective Use Electricity And Stop Wastage
To be conscious about putting off the light, fan, and air-conditioners
in houses and offices unless their uses become essential.
❏To use florescence or energy saving bulbs to save electricity
To avoid the use of electricity for cooking and use pressure cooker
which saves25% energy.
❏ Not to use air-conditioner unnecessarily
In buying refrigerators one should avoid bigger ones than needed.
❏ To produce their own needed electricity in bag factories using their
own generators, which will save energy transmission cost.
❏To take initiatives to use solar energy which is renewable.