Question

In the circuit shown in the adjoining figure the current between B and D is zero, the unknown resistance is of:

• A. 3 $\Omega$
• B. 2 $\Omega$
• C. 4 $\Omega$
• D. emf of a cell is required to final the value of X.

Answer 1

Answer: (B)

Equivalent resistance of $R_1$ and $R_2$ . $P=R_1+R_2=12+4=16\Omega$ Equivalent resistance of $R_3$ and $R_4$ $Q=1+3=4\Omega$ Equivalent resistance of $R_5$ and $R_6$ $R=\frac{1\times 1}{1+1}=\frac{1}{2}\Omega$ For no current in arm BD, bridge should be balanced. $\frac{P}{Q}=\frac{R}{S}$ $\frac{16}{X}=\frac{4}{1/2}$ $\frac{16}{X}=8$ $\Rightarrow$ $X=2\Omega$