a cell supplies a current of 1.2A through two 2 ohm resistors connected in parallel.When the resistors are connected in series,it supplies a current of 0.4 A.calculate the internal resistance and e.m.f. of the cell

Given R1 = R2 = 2Ω

Internal resistance = r

In parallel current flows = 1.2 A

In series current flows = 0.4A

Assuming that potential of the source remains constant in both cases.

Equivalent Resistance for Parallel connection

Thus, sum total of potential drops at individual resistance = total potential difference applied

--------------1.

Now, for series connection

Equivalent resistance together with the internal resistance in the series it becomes

Thus, sum total of potential drops at individual resistance = total potential difference applied

----------------2.

From eqn. 1 and eqn. 2