Question

In a metre bridge experiment, null point is obtained at $20cm$ 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 $4X$ against $Y$ will be at :

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

Answer 1

The correct option is A $50cm$

When X balanced against Y : $\frac{X}{Y}=\frac{20}{100-20}$ or

$Y=4X$

Let $l$ be the required balanced condition

so when 4X balanced against Y: $\frac{4X}{Y}=\frac{l}{100-l}$ or

$\frac{4X}{4X}=\frac{l}{100-l}$

or $100-l=l$

or $l=50cm$