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Cell having an emf ε 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:

1. V vs R (linear graph)
2. ε vs R (horizontal line)
3. ε vs R (linear graph)
4. V vs R (horizontal line)

Correct answer: V vs R (linear graph)

Solution

The potential difference V across the external resistance R is given by V = ε - Ir, where I = ε / (R + r). As R increases, the current I decreases, and V approaches ε asymptotically. This results in a linear increase in V with R for small values of R.

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