Question

(a) Name a device which helps to maintain a potential difference across the ends of a conductor.
(b) What is meant by saying that the potential difference between two points is 1 V?
(c) Define Ohm's law. Write an expression for it.
(d) What is the unit of resistance?
​(e) When the potential difference between the terminals of an electric heater is 110 V, a current of 5 A flows through it. What current will flow through the heater if the potential difference is increased to 220 V? What is the resistance of heater?

Answer 1

(a) The potential difference across the ends of a conductor is maintained by connecting a battery or a dry cell at the ends of the conductor.

(b) When 1 Joule of work is done to move a 1 Coulomb charge from one point to another, then the potential difference between the two points is said to be 1 Volt (V).

(c) According to Ohm's Law, the current flowing in a circuit is directly proportional to the applied potential difference.

Mathematical expression for Ohm's Law: $V\propto I$ or V = IR (Where 'R' is the constant of proportionality and is known as the resistance of the circuit)

(d) Unit of resistance is Ohm, denoted by the symbol $\mathrm{\Omega }$.

(e) According to Ohm's law, V = IR

$\Rightarrow R=\frac{V}{I}=\frac{110\mathrm{V}}{5\mathrm{A}}=22\mathrm{\Omega }$

Hence, the resistance of the heater is $22\mathrm{\Omega }$.

Now, if the potential difference is changed to 220 V, then the current in the circuit = $I=\frac{V}{R}=\frac{220\mathrm{V}}{22\mathrm{\Omega }}=10\mathrm{A}$