The following graph shows the variation of terminal potential difference V, across a combination of three cells in series to a resistor versus the current I :
(i) Calculate the emf of each cell. (ii) For what current I, will the power dissipation of the circuit be maximum ?

Answer

`1.4 V(`b)`1A`(c ) 0.7 Omega`

Explanation

(a) When `I = 0` , total emf = terminal voltage
`:. 4 epsilon = 5.6 V or epsilon = 1.4 V`
For the graph when when
`1 = 1.0A ,V = (2.8)/(4) = 0.7V` (for each cell)
(c) internal resistance of one cell `r = (epsilon)/(I_(max)) = (1.4)/(2.0) = 0.7 Omega`
(b) The output power is maximum when external resistance = total internal resistance
` = 4 r`
`I _(max) = ("total emf")/("total resistance") = (4 epsilon)/(4 r + 4 r) = (epsilon)/(2 r)`
` = (1.4)/(2 xx 0.7) = 1A`