Ohm's law: The electric current (i) in a conductor is proportional to the potential difference (V) between its ends of a constant temperature (T).

Verification: To verify Ohm's law, a battery; (B), ammeter (A). resistance (R), voltmeter (V), tap-key (K), rheostat (Rh) are connected as shown in circuit diagram. Voltage (v) across the resistor can be recorded by voltmeter (V) and current (i) can be recorded by ammeter (A) in the table given below and the ratio V/i can be calculated. Repeat the experiment five times by changing current in the circuit with the help of rheostat. Note the readings in the table.

From the above table it is observed that the ratio v/i is always constant. Hence ohm's law is verified. i.e., The resistance of a conductor remains constant at constant temperature no matter what applied voltage is used to measure it.