Q. A battery has an emf of 15V and internal resistance of 1$\Omega$. Is the terminal to terminal potential difference less than, equal to or greater than 15V if the current in the battery is (1) from negative to positive terminal, (2) from positive to negative terminal (3) zero current?
A) Less, grater, equal
B) Less, less, equal
C) Greater, greater, equal
D) Greater, less, equal
Explanation
(a) If E is the emf of the battery, r the internal resistance, i the current drawn and V the PD across the plates of battery, then
$V = E - ir$
Case I When the direction of current in the battery is from –ve to +ve or outside +ve to –ve, then
$i = + ve\ \ \ \ \ \ \ \ \ \ \ \ $(during discharging)
V<E
Case II When the direction of current in the battery is form +ve to –ve or outside –ve to +ve, then
$i = - ve$ (during discharging)
$V = E + ir$
$\Longrightarrow$V>E
Case III When zero current, then
$i = o$
$V = E$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.