Fig. 32. Measurement of resistance by substitution.
Let R be a variable resistance which can be changed in small steps, say of 0.1 Ω.
(i) Refer Fig. 32 (a). First resistance X is put in the circuit and the value of current noted.
Then resistance X is removed and it is substituted by a known variable resistance R which is varied so that the value of the current is same in both the cases. This value of R is equal to the unknown resistance.
(ii) If R is of fixed value note the readings of the ammeter for the following cases:
- For resistances X and R in series.
- When resistance X is removed.