Acell supplies a current of 0.6a through a 2 ohms coil and a current of 0.2a through a 7 ohms coil. calculate the e. m.f. of the cell.

E.M.F = 1.5 V

Explanation:

The equation relating EMF, internal resistance and external resistance is given by;

E = Ir + IR

Where; E is the EMF, I is the current, r is the internal resistance, and R is the external resistance.

Therefore;

When I = 0.6 A and R = 2Ω

E = 0.6 r + (0.6 × 2)

E = 0.6r + 1.2

When I = 0.2 A and R = 7 Ω

E = 0.2 r + (0.2 × 7)

E = 0.2 r + 1.4

Solving simultaneously;

E = 0.6r + 1.2

E = 0.2 r + 1.4 ; eliminating E

0 = 0.4 r - 0.2

0.4 r = 0.2

     r = 0.5

Therefore;

E = 0.2(0.5) + 1.4

   = 0.1 + 1.4

   = 1.5 V