Question

If $i=0.25\text{A}$. in the figure, then the value of $R$ is

• A. $48\Omega$
• B. $12\Omega$
• C. $120\Omega$
• D. $42\Omega$

Answer 1

The correct option is D $42\Omega$


From the figure, Equivalent resistance of the resistors within the loop is given by,

$\frac{1}{R_{eq}}=\frac{1}{60}+\frac{1}{20}+\frac{1}{10}$

$\therefore R_{eq}=6\Omega$

Now the equivalent resistance of circuit is , $R_{eq}^{\prime }=6+R$

But from Ohm's law, $R_{eq}^{\prime }=\frac{V}{i}$

$\Rightarrow 6+R=\frac{12}{0.25}$

$\therefore R=42\Omega$

Hence, option (d) is the correct answer.