The filament of a bulb takes a current 100 mA when potential difference across it is 0.2 V. When the potential difference across it becomes 1.0 V, the current becomes 400 mA. Calculate the resistance of filament in each case and account for the difference.

The specific resistance of copper, silver and constantan are 1.78 x 10^-6 Ω cm, 10^-6 Ω cm and 48 x 10^-6 Ω cm respectively.

(i) Identify the best conductor.

(ii) Give reason for your answer above.

The emf of a cell depends on :

1. the material of electrodes
2. the shape of electrodes
3. the distance between the electrodes
4. the amount of electrolyte in the cell

Emf of a cell is …………… the terminal voltage when cell is not in use, while …………… the terminal voltage when cell is in use.

1. greater than, smaller than
2. smaller than, greater than
3. equal to, greater than
4. equal to, smaller than