question_answer

A resistance R is to be measured using a meter bridge. Student chooses the standard resistance S to be 100\[\Omega \]. He finds the null point at \[{{l}_{1}}\] = 2.9 cm. He is told to attempt to improve the accuracy. Which or the following is a useful way?

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 meter bridge.

Correct Answer: C

Solution :

Option [c] is correct.

Explanation: To calculate resistance, R

=\[100\left[ \frac{2.9}{97.1} \right]\]

So to get balance point near to 50 cm (middle) we have to take S = 3\[\Omega \] , as here R : S =2.9 : 97.1 implies that S is nearly 33 times to R.

In order to make ratio R and S = 1:1, we must take the resistance S = 3\[\Omega \], which verifies options (C).