SSC JE Electrical Engineering 26 Sep 2019 Shift 1 Paper

Question : 126 of 200

Marks: +1, -0

Three lamps are connected in series across a 120Vsupply and take a current of 1.5A. If the resistanceof two of the lamps is 30Ω, what is the resistanceof the third lamp?

20Ω
30Ω
40Ω
10Ω

Validate

Solution:

Applying KVL,

- 120 + 1.5(R_1 + R_2 ) + 1.5R_3 = 0

- 120 + 1.5(30 + 30) + 1.5R_3 = 0

- 120 + 1.5(60) + 1.5R_3 = 0

-120 + 90 + 1.5R_3 = 0

1.5R_3 = 30

R_3 =300/15

∴

R_3 = 20Ω

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