Question

In the circuit shown below, if ammeter read $1\text{A}$, then the value of unknown resistance $X$ is

• A. $1\Omega$
• B. $2\Omega$
• C. $4\Omega$
• D. $3\Omega$

Answer 1

The correct option is B $2\Omega$

Equivalent resistance of the circuit is:
$R_{eq}=4+\frac{3\times (4+X)}{3+(4+X)}$
According to the question, current in the circuit is $1\text{A}$.

$I=\frac{V}{R_{eq}}$
$\Rightarrow 1\text{A}=\frac{6}{R_{eq}}$
$\Rightarrow 1=\frac{6}{4+\frac{3\times (4+X)}{3+(4+X)}}$
Solving, we get, $X=2\Omega$
Hence, the correct answer is option (b).