A resistance R is to be measured using a meter bridge. Student chooses the standared resistance S to be `100 Omega`. He finds the null point at `l_(1)=2.9cm`. He is told to attempt to improve the accuracy. Which of the folllowing is a useful way?

Options

A. He should measure `L_(1)` more accurately
B. He should change S to `1000 Omega` and repeat the experiment
C. He should change S to `3 Omega` and repeat the experiment
D. He should give up hope of a more accurate measurement with a metre bridge

Answer

C

Explanation

The metre bridge is most sensitive or gives maximum accuracy, when the null point is near the centre i.e.
`L_(1)=50 cm`
In this case, for the metre bridge,
`(R )/(S)=(L_(1))/((100-L_(1)))=(2.9)/(97.1)`
i.e. the value of S is nearly 33 times to that of R. To make this ratio = 1 : 1, S should be reduced to `1//33` times i.e. he should change 3 to `3 Omega`.