Question

A cell 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.

Answer 1

Answer:

1.5 V

Explanation:

Let the cell resistance be r.

For the first circuit we analyze it as follows :

The internal resistance of the cell. is constant.

Current = 0.6 A

R = 2 Ohms

V(emf) = I(Total resistance)

Total resistance = r + 2

V(emf) = 0.6(r + 2)

= 0.6r + 1.2

The second circuit:

Current = 0.2 A

Resistance = 7 ohms

V(emf) = 0.2(r + 7) = 0.2r + 1.4

We equate the two as follows :

0.2r + 1.4 = 0.6r + 1.2

1.4 - 1.2 = 0.6r - 0.2r

0.2 = 0.4r

r = 0.2/0.4 = 0.5

Substituting this we have :

0.6(0.5 + 2) = 2.5 × 0.6 = 1.5 V

The emf of the cell is 1.5 V.