A cell of emf ' `epsi` ' and internal resistance 'r' is connected across a variable resistor 'R'. Plot a graph showing the variation of terminal potential 'V' with resistance R. Predict from the graph the condition under which 'V' becomes equal to `' epsi ' `

Explanation

The terminal potential difference
`V = IR = (epsi)/((R+r)) .R (epsi)/((1+r/R))`
Thus as R increases, V also increases. Graph is shown in adjoining Fig. From the graph it is clear that V becomes equal to `epsi`, when R becomes `oo`