Question

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 $l_2=2.9cm$. He is told to attempt to improve the accuracy. Which of the following is a useful way?

• A. He should measure $l_2$ 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

Answer 1

Answer: (C)

As the meter bridge is balanced,
$\therefore \frac{R}{S}=\frac{l_1}{(100-l_1)}$,
or $R=\frac{S{l}_1}{(100-l_1)}$
$\frac{(100\Omega )(2.9cm)}{(100-2.9)cm}\approx 3\Omega$
The accuracy of measuring $R$ can be improved if $S$ and $R$ are of the same order, i.e., $S$ should be changed to $3\Omega$