A resistance R is to be measured using a meter bridge. A student chooses the standard resistance S to be 100 Ω. He finds the null point at l= 2.9 cm. He is told to attempt to improve accuracy. Which of the following is a useful way?
 

1. He should measure l1 more accurately
2. He should change S to 1000  Ω and repeat the experiment
3. He should change S to 3  Ω and repeat the experiment
4. He should give up hope of more accurate measurement with a meter bridge

(c) Hint: To reduce the error, the value of S should of the order of R.

Step 1:

The percentage error in R can be minimized by adjusting the balance point near the middle of the bridge, ie., when I1 is close to 50 cm. This requires a suitable choice of S.

Since, RS=l1(100l1)=l1100l1

Step 2:

Since here, R: S=2.9: 97.1 implies that the S is nearly 33 times 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 3Ω.