Q. Three similar cells, each of emf 2V and internal resistance $r$ send the same current through an external resistance of 2$\Omega,$when connected in series or in parallel. The strength of current flowing through the external resistance is
A) 0.75 A
B) 1 A
C) 1.5 A
D) zero
Explanation
(a) In series, $i = \frac{3 \times 2}{3r + 2}\ \ $…(i)
In parallel, $i = \frac{2}{r/3 + 2} = \frac{2 \times 3}{r + 2 \times 3}$ …(ii)
From Eqs. (i) and (ii), $3r + 2 = r + 6\ or\ r = 2\Omega$
From eqs. (i), $i = \frac{3 \times 2}{3 \times 2 + 2} = 0.75A$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.