In a meter 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 lt Y`, then the new position of the null point from the same end, if one decides to balance a resistance of `4 X` against `Y` will be at.

Options

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

Answer

A

Explanation

`(X)/(Y) = (20)/(80) = (1)/(4)` or `Y = 4 X`
`(4X)/(Y) = (l)/(100 - l)` or `(4X)/(4X) = (l)/(100 - l)` or `l = 50 cm`