Practice portal › Alternating Current › Series LCR: Impedance and Phase

An A.C. voltage V=5 cos(1000t) V is applied to an L-R series circuit of inductance 3 mH and resistance 4 Ω. The value of the maximum current in the circuit is _____.

Asked in GUJCET 2017 · Current in a series LCR

• (1) 0.8 A
• (2) 1.0 A
• (3) 5/7 A
• (4) 5/(√7) A

Step-by-step solution

Why the other options are wrong

• (1) 0.8 is R/Z=4/5, the power factor of the circuit, not a current. The peak current is (V₀)/Z.
• (3) Adds R and X_L directly: 5/(4+3)=5/7 A. They are at right angles, so Z=√4²+3²=5 Ω.
• (4) Subtracts the squares instead of adding them: Z=√4²-3²=√7 Ω gives 5/(√7) A.

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.