#### Question

A cell of emf '*E*' and internal resistance '*r*' is connected across a variable load resistor R. Draw the plots of the terminal voltage *V* versus (i) *R* and (ii) the current *I*.

It is found that when *R* = 4 Ω, the current is 1 A and when R is increased to 9 Ω, the current reduces to 0.5 A. Find the values of the emf *E* and internal resistance r.

#### Solution

(i)

(ii)

When* R* = 4 Ω and *I* = 1 A

We know

Terminal voltage, *V* = *E* − *Ir*

*So, we have*

V = IR = 4 = E − Ir

or

E − r = 4 ..... (i)

When *R*' = 9 Ω and *I*' = 0.5 A

*V* = *IR *= 0.5 × 9 = *E* − 0.5*r*

*or*

*E − 0.5r = 4.5 ..... (ii)*

*Solving (i) and (ii), we get*

* r = 1 Ω and E = 5 V*

Is there an error in this question or solution?

Solution A Cell of Emf 'E' and Internal Resistance 'r' is Connected Across a Variable Load Resistor R. Draw the Plots of the Terminal Voltage V Versus (I) R and (Ii) the Current I. Concept: Cells, Emf, Internal Resistance.