In a meter bridge, null point is 20 cm, when the known resistance R is shunted by 10Ω resistance, null point is found to be shifted by 10 cm. Find the unknown resistance X.

RX=l100-lX=100-llRX=100-2020R=4RWhen known resistance R is shunted, its net resistance will decrease. Therefore, resistance parallel to this (i.e., P ) should also decrease or its new null point length should also decrease.R'X=l'100-l'=20-10100-(20-10)=19X=9R'4R=9R'=910R10+RSolving this equation, we getR=504ΩX=4R=4504X=50Ω