Question

In a meter bridge with R and S in the gaps, the null point is found at 40 cm from A. If a resistance of 30Ω is connected in parallel with S, the null point occurs at 50 cm from A. Determine the values of R and S.

Answer 1

in first case I₁ = 40cm

\(\frac{R}{S}=\frac{l_1}{100-l_1}\) \(\Rightarrow \frac{R}{S}=\frac{40}{60}=\frac{2}{3}\) ....(i)

in second case when S and 30Ω are in parallel balancing length I₂ = 50 cm, so

From (i) \(S=\frac{3}{2}R\)

Subtituing this value in (ii), we get

Also from equation (iii), S' = R