A few straings cells in series are to be charge from a `30V` d.c. supply The end of each cutt is `1.35V` and internal resistance is `0.1 Omega` The charging current is `3.0A` in this arrangement how many calls can be charge and what extra resistance is required be the connected in the circuit ?

Explanation

Let `n` be the maximum number of cells in series which can be change and `R` is the extra resistance required if `f` is the currentin the circuit then `(nr + R) 1 = 30 - n epsilon`
Hence `epsilon = 1.35 V, r= 0.1 Omega and t = 3.0A`
Thus `(n xx 0.1 + R) xx 3= 30 - n xx 1.35 n (1.35 + 0.3) + 3R =m 30 or 1.65 n + 3R = 50`...(i)
or `n + (3)/(1.65) R = (30)/(1.65) = 18 + (30)/(165) :. n = 3n and (3R)/(1.65) = (30)/(165) or R = 0.1 Omega`