Aim : To verify that resistance of a conductor is proportional to the length of the
conductor for constant cross-section area and temperature.
- Collect iron spokes of different lengths ; with same cross sectional areas.
- Make a circuit leaving gas between P and Q with a battery, ammeter and plug key.
- Connect one of the iron spoke say 10 cm length between P and Q.
- Measure the value of current using ammeter and note the value.
- Repeat this for other lengths of the iron spokes and note the corresponding values of currents.
- You will observe that the current decreases with increase in the length of the spoke.
- Thus the resistance of each spoke increases with increase in the length for a constant potential difference.
- From this, we conclude that the resistance ® of a conductor is directly proportional to its length (l) for constant cross-sectional area.
Therefore, R ∝ L
- We notice that the resistance was more when the cross - section area was less.
Therefore , R ∝ L/A
Thus we verify l and A