Let us find out.

Collect iron spokes of different lengths with the same cross sectional areas. Make a circuit as shown in fig.- 14. Connect one of the iron spokes, say 10cm length, between P and Q. Measure the value of the current using the ammeter connected to the circuit and note the value in your note book. Repeat this for other lengths of the iron spokes. Note corresponding values of currents in your note book. What do you notice? 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 activity, we can conclude that the resistance (R) of a conductor is directly proportional to its length (l) for a constant potential difference.

          i.e.
R ∝ l (at constant temperature and cross sectional area)
          .................. (1)

Collect iron rods of equal lengths but different cross section areas. Make a circuit as shown in fig.- 14. Connect one of the rods between points P and Q. Note the value of the current using the ammeter connected to the circuit and note it in your note book. Repeat this with other rods. Note the corresponding values of currents in each case and note them in your note book. You will notice that the current flowing through the rod increases with increase in its cross sectional area. Hence, the resistance of a rod decreases with increase in the cross section area of the rod.

       From this activity, we conclude that the resistance of a conductor is inversely proportional to its cross section area.

          i.e.
R ∝ 1_A (at constant temperature and length of the conductor)           .................. (2)
From the equations (1) and (2), we get

R ∝l/A (at constant temperature)