Question

In a metre bridge experiment null point is obtained at $20\, cm$ from one end of the wire when resistance $X$ is balanced against another resistance $Y$. If $X < Y$, then where will be the new position of the null point from the same end, if one decides to balance a resistance of $4X$ against $Y$ ?

• A. 50 cm
• B. 80 cm
• C. 40 cm
• D. 70 cm

Answer 1

Answer: (A)

50 cm

Answer 2

We have from meter bridge experiment, $\frac{R_{1}}{R_{2}} = \frac{\ell_{1}}{\ell_{2}}$, where $\ell_{2} = \left(100-\ell_{1}\right)cm$ In the first case, $X/Y = 20/80$ In the second case $\frac{4X}{Y} = \frac{\ell}{100-\ell}$ $\ell = 50 \,cm.$