Electricity L6

Electric Potential
Electric potential at a point A in an electric field is the work done

per unit positive test charge in transporting it from infinitely far
away to the point A.
𝐖∞𝑨 ∞
V=
𝐪𝐎 q0
A
Electric Potential at any point

Electric potential is a scalar quantity.
Unit of electric potential
SI unit : Volt (V)
1 Volt = 1 Joule/coulomb = 1 J C-1

Electric Potential Difference
Potential difference between two points is defined as the work

done in carrying a unit positive charge from one point to
another point.
𝐖𝐀𝐁
VA-VB = q0 B
𝐪𝐎 A
Potential difference between two
points
Important Points
1 WAB = positive, if VA  VB ; WAB = negative, if VB  VA ;

WAB = 0, if VB=VA.
2 Potential difference between two points is independent of

actual path followed between the points.
Electric potential due to a point charge
Electric potential due to a point charge ‘q’ at a point P which is

located at a distance 'r' from it is given by
r
𝐊𝐪 𝟏 𝐪
V= = .
𝐫 𝟒𝝅𝜺𝟎 𝒓
q Electric potential P
due to point charge
Transferring charge completely from one body to another body
We can transfer the charge of a body completely if the charged

body is placed in a hollow conducting body and connected to its
inner surface through a conducting wire.
Transferring charge completely from one

charged body to another
The whole charge of the charged body will be transferred to the
hollow conducting body, as charge resides on its outer surface.
Also, the electric potential of inner charged body is always

greater than the electric potential of the outer surface of the
hollow conducting body.
This property is used in high voltage generators like Van de

Graff generator.
Question
How much work is done in moving a charge of 2C from

a point of 118V to a point of 128V?
(a) 20 J (b) 30 J
(c) 40 J (d) 10 J
Electric Current
The rate of flow of electric charge through any cross-section is

called ‘electric current’.
𝐐
I=
𝐭
Where, ‘Q’ is the charge that flows across the area in time ‘t’.
Important Points
Electric current is a scalar quantity.
Reason
Though, a direction is associated with electric current, still it is
not considered as vector quantity because it does not obey the
vector laws but obeys scalar laws of addition.
Unit of electric current
SI unit Ampere
1 Ampere = 1 coulomb/sec = 1 Cs-1
Definition of 1 ampere
1 ampere is the electric current flowing through a conducting

wire when 1 coulomb charge flows through it in 1 second.
Current carriers
The charged particles which flow in particular direction to

produce electric current are called current carriers.
Examples
In solid conductors - free electrons
In liquids - positive ions and negative ions
In gases - positive ions and free electrons

QUESTION
If the current in a household appliance is 5A, calculate the
amount of charge that passes through the appliance in 1 hour.
QUESTION
It is observed that electric charge of 6 x 102 C flows through a
given cross-section of conductor in 20 minutes time. What is
the strength of electric current in conductor ?
Electromotive Force (emf)
Electric current is possible in a closed circuit if

there is a source of external force which compels
the current to move in a definite direction.
(1) Battery or electrochemical cell
(2) Electric generators
(3) Solar cells
Electromotive Force (emf)
It is the maximum potential difference between the terminal of a

battery.
or
It is the maximum work done by source of emf in taking a unit
positive charge once around a closed circuit.
W
e=
Q
[Unit of emf : volt]

Terminal voltage (V)
It is the potential difference across the terminals of the source of

emf (like battery) in the external closed circuit.
A battery does not supply electrons to the circuit. It establishes

the electric field that exerts force on electrons already in the
wires and elements of the circuit.
Conventional Direction of Current
The conventional direction of electric current is ‘the direction of

flow of positive charge’. This means direction of electric current
is ‘opposite to the flow of negative charge’.
Flow of charge through a conductor
(a) When there is no potential difference across a conductor :

(b) When a potential difference is applied across the conductor.

Electricity L6

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Electric Potential

Electric potential at a point A in an electric field is the work done

Electric Potential at any point

Unit of electric potential

SI unit : Volt (V)

1 Volt = 1 Joule/coulomb = 1 J C-1

Potential difference between two points is defined as the work

1 WAB = positive, if VA  VB ; WAB = negative, if VB  VA ;

2 Potential difference between two points is independent of

Electric potential due to a point charge ‘q’ at a point P which is

We can transfer the charge of a body completely if the charged

Transferring charge completely from one

Also, the electric potential of inner charged body is always

This property is used in high voltage generators like Van de

How much work is done in moving a charge of 2C from

The rate of flow of electric charge through any cross-section is

Electric current is a scalar quantity.

1 Ampere = 1 coulomb/sec = 1 Cs-1

1 ampere is the electric current flowing through a conducting

The charged particles which flow in particular direction to

In solid conductors - free electrons

In liquids - positive ions and negative ions

In gases - positive ions and free electrons

Electric current is possible in a closed circuit if

It is the maximum potential difference between the terminal of a

[Unit of emf : volt]

It is the potential difference across the terminals of the source of

A battery does not supply electrons to the circuit. It establishes

The conventional direction of electric current is ‘the direction of

(a) When there is no potential difference across a conductor :

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