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AND
POTENTIAL
DIFFERENCE
POTENTIAL
11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE
11.2
11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE
11.2 ELECTRIC
11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCEELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE
What makes the electric charge to flow? Let us consider the analogy of
flow of water. Charges do not flow in a copper wire by themselves, just as
water in a perfectly horizontal tube does not flow. If one end of the tube
is connected to a tank of water kept at a higher level, such that there is a
pressure difference between the two ends of the tube, water flows out of
the other end of the tube. For flow of charges in a conducting metallic
wire, the gravity, of course, has no role to play; the electrons move only
if there is a difference of electric pressure – called the potential difference –
along the conductor. This difference of potential may be produced by a
battery, consisting of one or more electric cells. The chemical action within
a cell generates the potential difference across the terminals of the cell,
even when no current is drawn from it. When the cell is connected to a
conducting circuit element, the potential difference sets the charges in
motion in the conductor and produces an electric current. In order to
maintain the current in a given electric circuit, the cell has to expend its
chemical energy stored in it.
We define the electric potential difference between two points in an
electric circuit carrying some current as the work done to move a unit
charge from one point to the other –
Potential difference (V) between two points = Work done (W)/Charge (Q)
V = W/Q (11.2)
The SI unit of electric potential difference is volt (V), named after
Alessandro Volta (1745 –1827), an Italian physicist. One volt is the
potential difference between two points in a current carrying conductor
when 1 joule of work is done to move a charge of 1 coulomb from one
point to the other.
1 joule
Therefore, 1 volt =
1 coulomb
(11.3)

1 V = 1 J C –1
The potential difference is measured by means of an instrument called
the voltmeter. The voltmeter is always connected in parallel across the
points between which the potential difference is to be measured.

Example 11.2
How much work is done in moving a charge of 2 C across two points
having a potential difference 12 V?

Solution
The amount of charge Q, that flows between two points at potential
difference V (= 12 V) is 2 C. Thus, the amount of work W, done in
moving the charge [from Eq. (11.2)] is

Electricity 173

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