question_answer

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)

Correct Answer: B

Solution :

(b)             Current in the circuit, \[l=\frac{\varepsilon }{R+r}\] Potential difference across R,             \[V=lR=\left( \frac{\varepsilon }{R+r} \right)R=\frac{\varepsilon }{\left( 1+\frac{r}{R} \right)}\] When \[R=0,=0\,\,or\,\,R=\infty ,V=\varepsilon \]