AC Circuits
Maharashtra Board · Class 12 · Physics
Most important questions from AC Circuits for Maharashtra Board Class 12 Physics board exam 2026. MCQs, short answer, and long answer questions with marks.
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Sample Questions
A capacitor of 100 μF is connected to 50 Hz AC supply. The capacitive reactance is:
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31.8 Ω
Capacitive reactance XC = 1/(2πfC) = 1/(2 × 3.14 × 50 × 100 × 10^-6) = 1/0.0314 = 31.8 Ω. Capacitive reactance is inversely proportional to frequency and capacitance.
Which of the following statements about capacitive circuits are correct?
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Current leads voltage by 90°, Capacitive reactance decreases with frequency, Average power consumed is zero
In capacitive circuits: (1) Current leads voltage by 90° because current flows to charge/discharge the capacitor before voltage builds up, (2) XC = 1/(2πfC) shows inverse relationship with frequency, (3) Average power = 0 as energy oscillates between source and capacitor.
The impedance of a series LCR circuit with R = 3Ω, XL = 4Ω, and XC = 4Ω is:
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3 Ω
Impedance Z = √[R² + (XL - XC)²] = √[3² + (4 - 4)²] = √[9 + 0] = 3 Ω. When XL = XC, the circuit is at resonance and impedance equals resistance.
At resonance in a series LCR circuit:
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Current is maximum
At resonance, XL = XC, so impedance Z = R (minimum value). Since I = V/Z, minimum impedance gives maximum current. The circuit behaves as purely resistive with power factor = 1.
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