Question

In a meter bridge experiment, a 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 and if one decides to balance a resistance of 4x against y, then the new position of the null point from the same end is,

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

Answer 1

The correct option is A 50 cm

Here in meter bridge experiment length of wire l(say) is 100cm. Hence

$l_2=(100-l_1)cm$

where $l_1$ is the length of wire from one end upto null point, $l_2$ is the length of wire from null point to another end of wire.

Hence, in the first case,

$\frac{x}{y}=\frac{l_1}{l_2}$

$\frac{x}{y}=\frac{20}{80}$

Now, in the second case

$\frac{4x}{y}=\frac{l_1}{l_2}$

$\frac{4x}{y}=\frac{l_1}{(100-l_1)}$

$4\left(\frac{20}{80}\right)=\frac{l_1}{100-l_1}$

$\therefore l_1=50cm$