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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.

a
25 Ω
b
50 Ω
c
75 Ω
d
100 Ω

detailed solution

Correct option is B

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

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Similar Questions

If we use 100Ω and 200Ω in place of R and X we get null point deflection, l=33 cm . If we interchange the resistors, the null point length is found to be 67 cm. Find end corrections α and β.


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