Question

In the circuit shown below, the ammeter reading is zero. Then the value of the resistance $R$ is:

• A. $50\Omega$
• B. $100\Omega$
• C. $200\Omega$
• D. $400\Omega$

Answer 1

Answer: (B)

$100\Omega$

As the ammeter reading is zero, thus current flowing in the loop $II$ is zero.

Let the current flowing in loop $I$ be $i$ (clockwise)

$\therefore$ Potential across $R$ must be equal to $2V$ i.e $V_{QP}=2V$

$\therefore$ $2=iR$ $⟹i=\frac{2}{R}$ .........(1)

In loop $I$ : $12=i(500+R)$ ..........(2)

Using (1) we get , $12=\frac{2}{R}\times (500+R)$

or, $6R=R+500$

$\therefore$ $5R=500$ $⟹R=100\Omega$