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In a meter bridge, null point is 20 cm, ...

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

A

`10 cm`

B

`20 cm`

C

`30 cm`

D

`40cm`

Text Solution

Verified by Experts

The correct Answer is:
B
Initially `l_1/(100-l_1)=X/R=2/3`
`:l_1=2/5xx100`
`=40cm`
Finally, `l_2/(100-l_2)=X/R'=12/8=3/2`
`:. L2=3/5xx100`
`=60 cm`
`:. J` is displaced by
`l_(2) - 1_(1) = 20`cm
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