In a meter bridge experiment, the 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 where will be the new position of the null point from the same end, if one decides to balanced a resistance of `4X` against `Y`?

Options

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

Answer

A

Explanation

X is smaller than Y ,so `X//Y = 20/80 = 1/4` So we get `Y = 4X `
Let balancing length is I when resistance 4X is connected instead of X
So, `(4X)/Y = l/(100 - l)`
`therefore (4X)/(4X) = l/(100 - l)`
`therefore 2l = 100`
`therefore l = 50 cm`