In a metre bridge experiment null point is obtained at 40 cm from one end of the wire when resistanc

Question

In a metre bridge experiment null point is obtained at 40 cm from one end of the wire when resistance $X$ is balanced against another resistance $Y$. If $X<Y$, then the new position of the null point from the same end, if one decides to balance a resistance of $3 X$ against $Y$, will be close to\

Professor PC Thomas Classes · Answer

(c) : According to the metre bridge experiment,\ $\frac{X}{Y}=\frac{40}{60}$ 
$Y=\frac{3}{2} X$ .....(i)
 Now new position of null point is,\ $\frac{3 X}{Y}=\frac{l}{100-l} \Rightarrow \frac{6 X}{3 X}=\frac{l}{100-l} \quad($ from $(\mathrm{i}))$\ So, $200-2 l=1 \Rightarrow l=67 \mathrm{~cm}$\