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? ā(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?

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Solution

## (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 $⇒R=\frac{V}{I}=\frac{110\mathrm{V}}{5\mathrm{A}}=22\mathrm{\Omega }$ 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 = $I=\frac{V}{R}=\frac{220\mathrm{V}}{22\mathrm{\Omega }}=10\mathrm{A}$

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