(a) Derive a relation between the internal resistance, emf and terminal potential difference of a cell from which current I is drawn. Draw V vs I graph for the cell and explain its significance.
(b) A voltmeter of resistance `988 Omega` is connected across a cell of emf 2 V and internal resistance `2 Omega`. Find the potential difference across the voltmeter and also across the terminals of the cell. Estimate the percentage error in the reading of the voltmeter.

Explanation

(a) Consider the circuit shown.

By Kirchhoff.s rules we have `E - IR - rI = 0`
`E-V - Ir = 0`
`E= V + Ir`
The V-I graph is as shown.

Significance of Graph: To find emf and internal resistance of the cell.
(b) The diagram is as shown:

`V= E-Ir`
`998 xx I =2 -2I`
I= 0.002A
Therefore, `V= 0.002 xx 998 = 1.996V`
Percentage error `=(2-1.996)/(2) xx 100 = 0.2`%