Question

A resistance R is to the measured using a meter bridge. Student chooses the standard resistance S to be $100 \Omega$He finds the null point at He is told to attempt to improve the accuracy. Which of the following is a useful way?

• A. He should measure more accurately.
• B. He should change S to $100 \Omega$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.

Answer 1

Answer: (C)

He should change S to$3 \Omega$and repeat the experiment.

Answer 2

: As the meter bridge is balanced,

$\therefore \frac { \mathrm { R } } { \mathrm { S } } = \frac { 1 _ { 1 } } { \left( 100 - 1 _ { 1 } \right) }$

or $\mathrm { R } = \frac { \mathrm { Sl } _ { 1 } } { \left( 100 - \mathrm { l } _ { 1 } \right) } = \frac { ( 100 \Omega ) ( 2.9 \mathrm {~cm} ) } { ( 100 - 2.9 ) \mathrm { cm } } \approx 3 \Omega$

The accuracy of measuring can be improved if S and R are of the same order, i.e., S should be changed to $3 \Omega$ .