A series L R circuit connected with an ac source E = ( 25 sin 1000 t ) V has a power factor of 1 2 . If the source of emf is changed to E = ( 20 sin 2000 t ) V , the new power factor of the circuit will be :

Question

A series L R circuit connected with an ac source E = ( 25 sin 1000 t ) V has a power factor of 1 2 . If the source of emf is changed to E = ( 20 sin 2000 t ) V , the new power factor of the circuit will be :, 1 2, 1 3, 1 5, 1 7

MARKS App · Accepted Answer

For L R circuit, cos ϕ = R X L 2 + R 2 = 1 2 ⇒ R = X L Now, ω ' = 2 ω Therefore, X L ' = ω ' L = 2 ω L = 2 X L Hence, cos ϕ ' = R 2 X L 2 + R 2 = 1 5

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