Looking for classes? Ksquare Career Institute, Bengaluru →
A cell having an emf $\varepsilon$ and internal resistance r is connected across a variable external resistance R. As the resistance R is increased, the plot of potential difference V across R is given by
A
- 
B
- 
C
- 
D
- 
Detailed Solution
Current in the circuit: $I = \frac{\varepsilon}{R + r}$
$V = IR = \frac{\varepsilon R}{R + r} = \frac{\varepsilon}{1 + \frac{r}{R}}$
At R = 0, V = 0. As R increases V increases, but not linearly, and approaches $\varepsilon$ as R → ∞.
So the graph starts from the origin and rises as a curve that flattens towards the value $\varepsilon$.