Question

Find the value of r in the given circuit so that maximum power is generated in external circuit as shown in
the figure.

• A. $r=10\Omega$
• B. $r=20\Omega$
• C. $r=30\Omega$
• D. $r=40\Omega$
• E. $r=50\Omega$

Answer 1

Answer: (C)

$r=30\Omega$

Redrawing the given circuit to its equivalent circuit
we get the equivalent resistance $r_{eq}$ as
$r_{eq}=\frac{4r}{3}$
Maximum power, P is generated when internal resistance, r' of source is equal to total external resistance $r_{eq}$
Hence,
$r_{eq}=r^{\prime }$
$\frac{4r}{3}=40$
$r=30\Omega$