Question

An unknown resistance ‘X’ is placed in the left gap and a known resistance of 60Ω is placed in the right gap of a metre bridge. The null point is obtained at 70 cm from the left end of the bridge. Find the unknown resistance. 

Answer 1

Given: R = 60Ω, l₁ = 70 cm, 

l₂ = 100 - 70 = 30 cm

To find: Unknown resistance (X)

Formula: X/R = l₁/l₂

Calculation: From formula,

X/60 = 70/30

∴ X = 140Ω