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2. Electric Current
The rate of flow of charge at unit time. The
S.I Unit of current is ampere ( A )
I = q/t
I  Current
q  Total Charge
t  Time taken

5. The electricity that we use in our houses,
schools and factories is obtained from
power stations.
The electric power thus produced is
used through circuits and controlled by
switches.

6. Three Kinds of Circuits
Flow of current requires a close conducting
path. This path is made b connecting a cell or a
battery, a switch (key) and a bulb by means of
wires. This closed conducting path is known as an
electric circuit.
1. Simple circuit
2. Series Circuit
3. Parallel Circuit

8. Simple circuit
A circuit made up of a cell, a switch and a
bulb is known as a simple circuit .When the
switch is put on, the bulb glows. This is because
there is a continuous or closed path for the electric
current to flow.

9. Series Circuit

10. At the circuit, it is obvious that the bulbs
are connected end to end. This type of circuit is
known as series circuit. Here the current can
flow only in one direction and the same amount
of electric current flows through all the bulbs.
when one of the bulbs in the circuit is
removed or the bulb is fused. The other bulbs
will not glow because the circuit is not
complete now.

11. Parallel Circuit

12. Here each bulb is connected to the battery
terminals by separate wires. This type of circuit
is known as parallel circuit.
In this circuit different amount of current
passes through the bulbs. It have separate
conducting paths

13. Functions of various electric components
1) Source of current
2) Key
3) Connecting Wires
4) Ammeter
5) Voltmeter
6) Galvanometer
7) Load

15. Source of current
There are two types of current sources :
i) alternating current (a.c) source
such as mains in our house and a.c generator.
ii) direct current (d.c) source such
as a cell or a battery

16. The purpose of Source of current is
supply electric current in a circuit.
Used in a laboratory,
* leclanche cell
* daniel cell
* lead accumulator (storage cell)

17. A cell giving the direct current(d.c) is
represented by two vertical lines of unequal
lengths. The longer is one marked ‘+’ to represent
anode while the shorter is marked ‘-’ to represent
cathode.
If an alternating current (a.c) source is used,
it is represented by a sine curve with in a circle.

18. Key
It is used to put the current on and
off in a circuit.
* plug key
* switch
* tapping key

19. When Key is open the circuit is
incomplete and is called an open circuit.
When key is closed, current flows
through the circuit and is called an closed
circuit.

20. Connecting Wires
The wires used to connect various
electrical components. They are made of
highly conducting metal such as copper or
aluminium .
A connecting wire may be just a thick
wire.
In an electric circuit, connecting wire is
represented simply by a line.

21. Description of
Ammeter and Voltmeter

23. Ammeter

24. Ammeter
The current flowing in a circuit is measured
by an ammeter. It has a circular scale graduated
in amperes.

25. An Ammeter is connected in series in a
circuit.
The terminal (+) is connected to the positive
terminal of the cell and the terminal (-) is
connected to the negative terminal of the cell
through the other electrical components.

26. Voltmeter

27. Voltmeter
The Potential difference between the two
points of a circuit is measured by a voltmeter.
It has a graduated scale in volts.

28. A Voltmeter is connected in parallel across
the two points between which potential difference
is to be measured.
The terminal (+) is connected to the point
which is connected to the positive terminal of the
cell and the terminal (-) is connected towards the
negative terminal of the cell.

29. Galvanometer

30. Galvanometer
A galvanometer is used when we
want to detect the presence of very
weak current in an electric circuit or to
know the direction of flow of current
in a circuit.

31. It does not measure the magnitude of
current in a circuit.
It is joined in a circuit in series just
like an ammeter.
It is symbolically represented by the
letter G enclosed in a circle.
The deflection of needle on it shows
the presence of current and direction of
deflection indicates the direction of flow of
current.

32. Load
An appliance which is connected
in a circuit is called load.
Ex : bulb , heater , etc…

33. Electric Charge
The fundamental unit of electric
charge (e) is the charge carried by the
electron and its unit is coulomb. ‘e’ has the
magnitude 1.6 x 10 -19
charge q = ne

34. Types of charges
1.There are two kinds of charges.
a). Positive charge
b). Negative charge
2. There is a force between the two charges
3. Like charges (positive and positive) or
(negative and negative) repel each other.
4. Unlike charges (positive and negative)
attract each other.

35. Conductors
The substance which allow the current
to flow through them easily are called the
conductors.
The human body also allows current to
flow through it, so it is also a conductor.
Ex : copper, aluminium, silver, iron

37. Insulators
The substance which do not allow the
current to flow through them, are called the
insulators.
Ex : rubber, plastic, wood, paper, glass

39. Potential difference
The electric potential difference is the
difference in electric potential (V) between the
final and the initial location when work is done
upon a charge to change its potential energy.

40. The standard metric unit on electric
potential difference is the volt, abbreviated V.
In equation form, the electric potential
difference is

41. Electrical Resistance
The obstruction offered to the flow of
current by the wire is called its electrical
resistance.

42. Ohm’s Law
Ohm's law states that the current through
a conductor between two points is
directly proportional to the voltage across the two
points. Introducing the constant of proportionality,
the resistance.
The unit of resistance is ohm (Ω)

43. PROBLEMS:
1.A charge 0.5 C passes through a cross
section of a conductor in 5s. Find the current.
2. A current of 1.5 A flows through a
conductor for 2.0s. What amount of charge passes
through the conductor?
3. When starter motor of a car is switched
on for 0.8s,a charge 24 C passes through the coil
of the motor. Calculate the current in the coil.

44. ANSWERS:
1. 0.1 A
2. 3 C
3. 30 A

45. 4. Charge = 1.5 C , Work = 9 J , Find the
potential difference?
5. Potential difference = 12 V , Resistance =
24 Ω, find the current?
6. Current= 1.5 A , Potential difference = 6.0
V , Find the resistance?
7. Current = 0.2 A , Resistance = 15 Ω , Find
the potential difference?

46. ANSWERS:
4. 6 V
5. 0.5 A
6. 4 Ω
7. 3 V

47. Thank You