Question

Two lamps of resistance 30Ω and 20Ω respectively are connected in series in a 110V circuit. Calculate:
(i) the total resistance in the circuit
(ii) the current in the circuit, and
(iii) the voltage drop across each lamp.

Answer 1

(i) Since the two lamps are connected in series, their total resistance R is given by:

R = R₁ + R₂

= 30 Ω + 20 Ω = 50 Ω

(ii) We have, V = 110 volt, R = 50 Ω

∴ By Ohm's law

I = `"V"/"R" = 110/50`A = 2.2 A

(iii) We now have

I = 2.2 A

∴ V₁ = IR₁ = 2.2 × 30V = 66 V

∴ Voltage frop across L₁ = 66 V

Similarly, V₂ = IR₂ = 2.2 × 20 = 44 V

∴ Voltage drop across L₂ = 44 V.