Alternating Current — Previous-Year Questions

Q1. An AC source delivers v = 200 sin(100πt). Its rms voltage and frequency are:

Q2. Peak voltage of Indian household mains (230 V rms) is approximately:

Q3. Time period of a 60 Hz AC source is:

Q4. If v = 100 sin(314t + π/3), the phase angle at t = 0 is:

Q5. What is V_rms for the waveform v(t) = 50 V (a square wave switching ±50 V)?

Q1. A 100 Ω resistor is connected to a 220 V (rms), 50 Hz source. The rms current is:

Q2. Power dissipated in the same resistor is:

Q3. Phase difference between V and I in a pure resistor is:

Q4. For an AC source with V₀ = 50 V across R = 25 Ω, peak current is:

Q5. Average power in a pure resistive AC circuit equals:

Q1. Inductive reactance of a 200 mH inductor at 50 Hz is:

Q2. In a pure inductor, the current:

Q3. At DC steady state, a pure inductor behaves like:

Q4. Average power consumed by a pure inductor is:

Q5. If frequency is doubled, the impedance of a pure inductor:

Q1. Reactance of a 10 μF capacitor at 50 Hz:

Q2. In a pure capacitor, the current:

Q3. If frequency is doubled, X_C:

Q4. Average power in a pure capacitive AC circuit:

Q5. What does a capacitor do at very high frequency?

Q1. A series LCR has R = 30 Ω, X_L = 40 Ω, X_C = 0. Impedance:

Q2. Same circuit, V_rms = 100 V. Current is:

Q3. Phase angle in the previous circuit:

Q4. At resonance in a series LCR:

Q5. If V_R = 30 V, V_L = 60 V, V_C = 20 V in a series LCR (rms values), source voltage is:

Q1. Resonance frequency of an LCR series with L = 200 mH, C = 5 μF:

Q2. At resonance, impedance of a series LCR equals:

Q3. Q-factor of an LCR series with L = 4 mH, C = 1 μF, R = 4 Ω:

Q4. Doubling R in a series LCR circuit:

Q5. At resonance in a series LCR, voltage across L equals:

Q1. A circuit draws 10 A rms at 220 V rms with phase angle 60°. Real power consumed:

Q2. Apparent power in the same circuit:

Q3. Power factor of a pure capacitor or pure inductor is:

Q4. For maximum power transfer in AC, the load impedance should:

Q5. Why do industries add capacitors in parallel with inductive loads?

Q1. L = 0.02 H, C = 50 μF. Period of LC oscillation:

Q2. In an LC oscillation, at t = T/4 the energy is:

Q3. Capacitor initially has 5 mC at 100 μF. Peak current in an LC oscillation with L = 25 mH:

Q4. Mechanical analogue of an LC oscillator is:

Q5. If both L and C are doubled, the period of LC oscillation becomes:

Q1. A transformer has N_p = 200, N_s = 1000. Primary fed with 50 V AC. Secondary voltage:

Q2. Same transformer. If primary current is 5 A, secondary current is:

Q3. A transformer cannot work on DC because:

Q4. Why is electrical power transmitted at very high voltages?

Q5. Ideal transformer efficiency is:

Q1. A 100-turn coil of area 0.05 m² rotates at 50 rad/s in B = 0.2 T. Peak EMF:

Q2. If rotation speed of the generator coil doubles, what happens to peak EMF and frequency?

Q3. A 2-pole generator must spin at what speed to give 50 Hz?

Q4. EMF induced in a rotating coil is zero when:

Q5. Slip rings vs commutator: the difference is:

Q1. An inductor of L = 100 mH at f = 100 Hz. X_L is:

Q2. At what frequency does X_L = X_C for L = 1 H and C = 1 μF?

Q3. When frequency is doubled, X_C becomes:

Q4. At very high f, an LC series circuit behaves like:

Q5. Series RC circuit: at very low f, the output across R is:

Q1. An AC voltage v = 282.84 sin(ωt) volts. rms voltage:

Q2. If V_rms = 110 V, peak voltage is:

Q3. Indian mains supply is rated 230 V. This is:

Q4. A square wave of amplitude 10 V. rms value:

Q5. Why do we use rms instead of average for AC current?

Q1. In a series LCR phasor diagram, V_R = 40 V, V_L = 30 V, V_C = 60 V. Source voltage:

Q2. On a phasor diagram with current along +x, V_L is drawn:

Q3. Phase angle φ is positive when:

Q4. Two voltages V₁ = 10 sin(ωt) V and V₂ = 10 sin(ωt + 90°) V add to:

Q5. Phasor analysis works because: