If the resistance X and Y `(XltY)` be placed in the two gaps of a metre bridge , null point is obtained at a length of 20cm . Keeping Y unchanged if a resistance 4X is placed in place of X what will be the position of the null point ?

Explanation

In the first case , `(X)/(Y)=(20)/(100-20)`
`"or, " Y=4X`
So , if resistance 4X be palaced in place of X , resistance of the two gaps will be equal , since Y = 4 X .
Therefore , the null point will be at the middle of the bridge wire i.e , at 50 cm .