- Collect iron rods of equal lengths but different cross-section areas.
- Make a circuit leaving gap between P and Q as shown in figure.
- Connect one of the rods between P and Q and measure the current using ammeter and note values.
- Repeat this with the other rods and note the corresponding values of current in each case and note them.
- You will notice that the current flowing through the rod increases with increasing in the cross-section area of the rod.
- Thus the resistance of the rod decreases with increasing the cross-section area.
- From this we conclude that the resistance ® of a conductor is inversely proportional to its cross-section area (A).

.-. R $\propto$ l/A (at constant temperature and length of the conductor)