JEE Main 2024 Physics 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:
Answer: (C)
Solution
cosφ = R/√² + R²) = 1/√2 gives R = . When ω doubles, ′ = = 2R, so cosφ′ = R/√(4R² + R²) = 1/√5.