Alternating Current

33 solved questions from Class 12 Physics, each with the full working. Tap any question to see the step-by-step solution.

• 1 What is the fundamental law or governing principle of 'Alternating Current' in Class 12 Physics? medium MCQ Fundamental Physical Law
• 2 What is the SI unit and dimensional formula for the key physical quantity studied in 'Alternating Current'? medium MCQ SI Units & Dimensional Analysis
• 3 How does the field or potential intensity vary with distance r in 'Alternating Current'? medium MCQ Spatial Distance Dependence
• 4 What is the net flux or circulation integral through a closed surface in 'Alternating Current'? medium MCQ Gauss's Theorem & Boundary Integrals
• 5 Why do field lines in 'Alternating Current' never intersect each other? medium MCQ Field Line Properties
• 6 A transformer has a primary of 200 turns and a secondary of 50 turns. A 240 V rms AC voltage is applied to the primary at 50 Hz, and a load of 500 Ω is connected across the secondary. Calculate the secondary rms voltage and the secondary rms current. hard 5 marks Transformer turns ratio
• 7 An AC voltage source produces a sinusoidal voltage with peak value V_m=120 V. What is the RMS value of the voltage? easy 1 mark RMS voltage calculation
• 8 A series LCR circuit has R=10 Ω, L=0.5 H, C=100 µF and is driven at f=50 Hz by a 100 V rms source. Calculate the magnitude |Z| of the impedance and the phase angle varphi between the source voltage and current. medium 3 marks Series LCR impedance
• 9 An AC source produces a sinusoidal voltage with peak (maximum) value V_m=200 V. What is its rms value? easy MCQ 1 mark RMS value of sinusoidal voltage
• 10 A transformer has 400 turns on the primary and 100 turns on the secondary. A 240 V rms sinusoidal supply at 50 Hz is connected to the primary. The secondary is connected to a resistive load of 800 Ω. Find (a) the secondary rms voltage, and (b) the secondary rms current. medium 2 marks Transformer voltage and current ratios
• 11 A single‑phase load consumes P=3 kW at V=230 V rms, f=50 Hz and has a lagging power factor of cosφ=0.70. To improve the power factor to unity, a capacitor is connected in parallel with the load. What capacitance should be used?\n\nA) 120 μF\nB) 184 μF\nC) 250 μF\nD) 320 μF hard MCQ 3 marks Power factor correction with capacitor
• 12 A series RLC circuit consists of R=20 Ω, L=0.2 H and C=50 μF. It is connected to an AC source of rms voltage V=120 V and frequency f=60 Hz.\n(a) Show that the circuit is at resonance.\n(b) Find the rms current at resonance.\n(c) Calculate the quality factor Q of the circuit.\n(d) Determine the bandwidth Δ f (in Hz) of the circuit. hard 3 marks Resonance in series RLC circuit
• 13 A series RLC circuit has R=30,Ω, L=0.4,H and C=25,μF. It is connected to an AC source of 110,V rms at f=50,Hz. (a) Show that the circuit is at resonance. (b) Find the rms current at resonance. (c) Calculate the quality factor Q of the circuit. (d) Determine the bandwidth Δ f (in Hz) of the circuit. hard 4 marks RLC resonance and bandwidth
• 14 An AC source supplies a sinusoidal voltage with a peak value of V_m=300,V. What is its rms voltage? easy 1 mark RMS voltage calculation
• 15 A series LCR circuit has R=15,Ω, L=0.3,H, C=120,μF and is driven at f=60,Hz by a 250,V rms source. Calculate the magnitude |Z| of the impedance and the phase angle φ (in degrees) between the source voltage and current. hard 5 marks Impedance magnitude and phase angle
• 16 A transformer has 400 turns on the primary and 100 turns on the secondary. A 220,V rms sinusoidal supply at 50,Hz is connected to the primary. The secondary is connected to a resistive load of 200,Ω. Find (i) the secondary rms voltage and (ii) the secondary rms current. medium 2 marks Transformer voltage and current relations
• 17 An AC source has a peak voltage of 180 V. What is its rms voltage? easy 1 mark RMS conversion
• 18 A single‑phase AC load consumes P=4 kW at V=400 V rms, f=50 Hz, with lagging power factor cos φ = 0.65. A capacitor is connected in parallel with the load to bring PF to unity. What capacitance should be used? hard 4 marks Power factor correction with capacitor
• 19 A series RLC circuit has R=20\,Ω, L=0.6\,H, C=80\,μF and is driven at f=100\,Hz by a 200\,V rms source. Calculate the magnitude |Z| of the impedance and the phase angle φ (in degrees) between the source voltage and current. medium 3 marks Impedance of RLC series circuit
• 20 A transformer has 250 turns on the primary and 50 turns on the secondary. A 230 V rms sinusoidal supply at 50 Hz is connected to the primary. The secondary is connected to a resistive load of 400\,Ω. Find (i) the secondary rms voltage and (ii) the secondary rms current. medium 3 marks Transformer voltage and current relations
• 21 A series RLC circuit has R=35 Ω, L=0.45 H, C=60,muF and is driven by a 250 V rms source at 80 Hz. Find the magnitude of the impedance |Z| and the phase angle varphi (in degrees) between the source voltage and current. medium 3 marks Series RLC impedance
• 22 An AC source has a peak voltage of 240 V. Find its rms voltage. easy 1 mark RMS voltage conversion
• 23 A transformer has N_p=1200 turns on the primary and N_s=300 turns on the secondary. The primary is connected to a 240 V rms AC supply at 50 Hz and a resistive load of 600 Ω is connected across the secondary. Assuming copper loss is 2 % and core loss is 1 % of the primary power, calculate (i) the secondary rms voltage, (ii) the secondary rms current, (iii) the transformer efficiency. hard 5 marks Transformer efficiency with losses
• 24 A single‑phase AC load consumes P=5 kW at V=400 V_rms, f=50 Hz, and has a lagging power factor of cosφ=0.6. A capacitor is connected in parallel with the load to bring the power factor to unity. Calculate the required capacitance. hard 3 marks Power factor correction with capacitor
• 25 An AC source produces a sinusoidal voltage with peak (maximum) value of 480 V. What is its rms voltage? easy 1 mark AC voltage conversion
• 26 A series RLC circuit has resistance R = 50,Ω, inductance L = 0.2,H, and capacitance C = 100,μF. It is connected to a 200,V_rms sinusoidal source at 60,Hz. Calculate (i) the magnitude of the impedance |Z|, and (ii) the phase angle φ (in degrees) between the source voltage and current. medium 2 marks Series RLC impedance
• 27 A transformer has 1500 turns on the primary and 300 turns on the secondary. The primary is connected to a 240 V_rms AC supply at 50 Hz and a resistive load of 800 Ω is connected across the secondary. Copper loss is 3 % and core loss is 2 % of the primary power. Find (i) the secondary rms voltage, (ii) the secondary rms current, and (iii) the efficiency of the transformer. hard 4 marks Transformer operation with losses
• 28 A single‑phase AC load consumes P=7 kW at a rms voltage V=415 V and frequency f=50 Hz. The load has a lagging power factor cosφ = 0.78. A capacitor is connected in parallel with the load to improve the overall power factor to unity. Determine the required capacitance (in μF) and state the rms current drawn from the source after correction. hard 5 marks Power‑factor correction using a capacitor
• 29 A series RLC circuit has R = 40 Ω, L = 0.25 H and C = 80 μF. It is connected to a 230 V_rms source operating at f = 50 Hz. Calculate (i) the magnitude of the total impedance |Z|, and (ii) the phase angle φ (in degrees) between the source voltage and the current. medium 2 marks Impedance and phase angle in series RLC
• 30 An AC source has a peak voltage of 340 V. What is its rms voltage? easy MCQ 1 mark RMS value of sinusoidal voltage
• 31 A transformer has N_p=500 turns on the primary and N_s=125 turns on the secondary. The primary is connected to a 240 V_rms source at 50 Hz. The secondary supplies a resistive load of R_L=400 Ω. Copper loss in the windings is 4% of the input power and core loss is 3% of the input power. Determine the efficiency of the transformer (in %). medium 2 marks Transformer efficiency with copper and core losses
• 32 An AC voltage source produces a sinusoidal voltage with a peak value of 480 V. What is its rms value? easy MCQ 1 mark Conversion peak to rms voltage
• 33 A transformer has 800 turns on the primary and 200 turns on the secondary. The primary is connected to a 240 V_rms supply at 50 Hz, and the secondary supplies a resistive load of 600 Ω. Copper loss in the windings is 3% of the input power and core loss is 2% of the input power. Find (i) the secondary rms voltage, (ii) the secondary rms current, and (iii) the efficiency of the transformer (in %). easy 3 marks Transformer voltage, current, efficiency