Question

Four cells of identical $emf\epsilon$ and internal resistance $r$ are connected in series to a variable resistor. The following graph shows the variation of terminal voltage of the combination with current. The emf of each cell used is

• A. 1.4 V
• B. 5.6 V
• C. 2 V
• D. 1 V

Answer 1

Answer: (A)

Emf of each cell $=\epsilon$
Internal resistance of each cell $=r$
Number of cells $(n)=4$
Total $emf=n\epsilon =4\epsilon$
Total internal resistance $=nr=4r$
Terminal voltage, $V=4\epsilon -I(4r)$...(i)
From the graph, When $I=0,V=5.6V$
$\therefore$ From (i),
$5.6=4\epsilon -0$
$\epsilon =\frac{5.6}{4}=1.4V$