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 changes S to `1000 Omega` and repeat the experiment
C. He should changes S to `3 Omega` and repeat the experiment
D. He should given up hope of a more accurate measurement with a meter bridge

Answer

C

Explanation

The percentage error in R can be minimized by adjusting the balance point near the middle of the bridge, i.e., when `I_(1)` is close to 50 cm . This requires a suitable choice of S.
Since, `R/S = (RI_(1))/(R(100-l_(1))) = l_(1)/(100 - l_(1))`
Since here, `R : S :: 2.9 : 97.1` imply that the S is nearly 33 times to that of R . In order to make this ratio 1:1, it is necessary to reduce the value of S nearly `1/33` times i.e., nearly `3 Omega`