Question

In the circuit shown, the reading of ammeter is $2\text{A}$. The ammeter has negligible resistance. The value of $R$ equals

• A. $2\Omega$
• B. $4\Omega$
• C. $6\Omega$
• D. $8\Omega$

Answer 1

The correct option is C $6\Omega$

$\because R,2R$ and $3R$ are in parallel.
Let equivalent resistance of $R,2R$ and $3R$ be $R^{\prime }$.
$\therefore R^{\prime }=\frac{6R}{11}$
$\therefore R_{total}=\frac{5R}{11}+R^{\prime }=\frac{5R}{11}+\frac{6R}{11}=R$

Since $I=\frac{V}{R_{total}}$
$\Rightarrow 2=\frac{12}{R}$
$\therefore R=6\Omega$
Hence, the correct answer is (C).