Question

The power dissipated in the circuit shown in the figure is $30$ Watts. The value of $R$ is

• A. $20\, \Omega$
• B. $15\, \Omega$
• C. $10\, \Omega$
• D. $30\, \Omega$

Answer 1

Answer: (C)

$P=\frac{V^{2}}{R_{e q}}$
$\frac{1}{R_{e q}}=\frac{1}{R}+\frac{1}{5}=\frac{5+R}{5 R}$
$R_{e q}=\left(\frac{5 R}{5+R}\right) P=30\, W$
Substituting the values in equation (i)
$30=\frac{(10)^{2}}{\left(\frac{5 R}{5+R}\right)}$
$\Rightarrow R=10\, \Omega$