Question

In the a.c. bridge circuit shown in figure, at balance the parameters of the coil are calculated to be 50 mH and $20\Omega .$ Another coil is connected in parallel to the previous coil and balance is restored by changing $R_{2}to2.5k\Omega .$ The parameters of the new coil are then

• A. $25mH,20\Omega$
• B. $50mH,20\Omega$
• C. $50mH,10\Omega$
• D. $100mH,40\Omega$

Answer 1

The correct option is B $50mH,20\Omega$


At balance,


Since, $Z_{4}and{Z}_3$ are fixed.

So, if $Z_2$ is made half its value.

In order to maintain balance, $Z_1$ should also be made half.

$Z_1$ can be made half by connecting the coil of the exactly value as $Z_1$ is parallel to $Z_2$ is arm (1).

So, (b) is the correct option.