Question

In the circuit shown, 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

The correct option is B $100\Omega$

Since the current through the ammeter is zero, all the current passing from $500\Omega$ resistor passes through $R$.

$12-(500+R)i=0$

Also the potential difference across $R$ is $2V$ due to the external battery attached.

Thus $2=iR$

Solving the two equations gives $R=100\Omega$