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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.
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Solution
(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.
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