Q. When the resistance of $9\ \Omega$ is connected at the ends of a battery, its potential difference decreases from $40\ volt$ to $30\ volt.$ The internal resistance of the battery is
A) $6\ \Omega$
B) $3\ \Omega$
C) $9\ \Omega$
D) $15\ \Omega$
Explanation
(b) The internal resistance of battery is given by
$r = \left( \frac{E}{V} - 1 \right)R = \left( \frac{40}{30} - 1 \right) \times 9 = \frac{9 \times 10}{30} = 3\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.