Question

cell supplies a current of 0.9 A through a 2 ohm resistor and current of 0.3 A through a 7 ohm resistor. What is the internal resistance of the cell?

• A. 0.5 ohm
• B. 1 ohm
• C. 1.2 ohm
• D. 2 ohm

Answer 1

The correct option is A 0.5 ohm

If E the emf of the cell and r its internal resistance then
$\frac{E}{2+r}=0.9$ and
$\frac{E}{7+r}=0.3$
dividing the two equations we get
$\frac{7+r}{2+r}=\frac{9}{3}$
r=0.5 ohm