Question

(a) State Ohm's law.

(b) Describe an experiment to verify this law.

Answer 1

(a)The potential difference across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it, provided its temperature remains the same. This is called Ohm’s law.

(b) Experiment to verify Ohm's law:

Set up a circuit as shown in figure shown, consisting of a nichrome wire XY of length, say $0.5m$, an ammeter, a voltmeter and four cells of $1.5V$ each. First use only one cell as the source in the circuit. Note the reading in the ammeter $I$, for the current and reading of the voltmeter $V$ for the potential difference across the nichrome wire XY in the circuit. Tabulate them in a table. Next connect two cells in the circuit and note the respective readings of the ammeter and voltmeter for the values of current through the nichrome wire and potential difference across the nichrome wire. Repeat the above steps using three cells and then four cells in the circuit separately. Calculate the ratio of V to I for each pair of potential difference V and current I. In this experiment, we will find that approximately the same value for $\frac{V}{I}$ is obtained in each case. Thus the V–I graph is a straight line that passes through the origin of the graph, as shown in the figure. Thus, V/I is a constant ratio, which verifies Ohm's law.