JEE Main 2021 · Physics · Electromagnetic Induction and Alternating Current · easy

A series circuit contains a resistor R=30 Ω, an inductor and a capacitor, driven by a 150 V (rms) source. At the source frequency the inductive…

Single correct option

A series circuit contains a resistor

R=30\ \Omega

, an inductor and a capacitor, driven by a

150\ \mathrm{V}

(rms) source. At the source frequency the inductive reactance is

40\ \Omega

and the capacitive reactance is

80\ \Omega

. If the frequency is varied until the current is maximum, the average power dissipated becomes

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Answer: (C) $750\ \mathrm{W}$

At the given frequency

Z=\sqrt{30^2+40^2}=50\ \Omega

, so

I=3\ \mathrm{A}

and

P=I^2R=270\ \mathrm{W}

(this is the trap option). At resonance

X_L=X_C

, so

Z=R=30\ \Omega

and

I=150/30=5\ \mathrm{A}

. Then

P=I^2R=25\times30=750\ \mathrm{W}

Original question written in the JEE Main 2021 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake