The diagram shows three resistors connected across a cell of emf 1.8 V

Electricity and Magnetism (10)

The diagram above shows three resistors connected across a cell of e.m.f. 1.8 V and internal resistance r. Calculate:

 

1. Current through 3 W resistor.
2. The internal resistance r.

Answer

(i) I_3Ω = (0.3 x 1.5)/(3 + 1.5)

= 0.45/4.5

= 0.1 A

(ii) R₁ = (1.5 x 3)(1.5 + 3) = 1Ω

R = 1Ω + 4Ω = 5Ω

E = I(R + r)

1.8 = 0.3(5 + r)

r = 1.8/0.3 - 5 = 1Ω