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 `I_(1)` more accurately
B. He hould change S to `1000Omega` and repeat the experiment
C. He should change S to `3Omega` 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 minimised by adjusting the balance point near the middle of the bridge, i.e., when `I_(1)` in close to 50 cm. this requires a suitable choice of S.
Since, `(R)/(S)=(Rl_(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 orded to make this ratio 1:1, it is neccesary to reduce the value of S nearly `(1)/(33)` times i.e., nearly `3Omega`.