Class 12 Physics MCQ Chapter 7 Alternating Current
Enhance your board exam preparation with our Class 12 Physics MCQ Chapter 7 Alternating Current English Medium collection. This article provides a carefully prepared set of multiple-choice questions (MCQs) with answers, helping AHSEC Higher Secondary students gain a strong understanding of one of the most important chapters in Physics.
The chapter Alternating Current introduces students to the principles and applications of AC circuits. It covers essential topics such as alternating voltage and current, peak value, RMS value, reactance, impedance, phase difference, power factor, LC oscillations, transformers, and AC circuit analysis. These concepts are frequently tested in board examinations and are crucial for understanding modern electrical systems.
All MCQs are designed according to the latest AHSEC syllabus and examination pattern, making them highly useful for revision and self-assessment. By practicing these objective questions regularly, students can improve their conceptual clarity, strengthen numerical problem-solving skills, and increase confidence before examinations.
Whether you are preparing for school tests, model exams, or the AHSEC Higher Secondary Final Examination, these Chapter 7 MCQ solutions will help you revise important concepts effectively and achieve better results in Physics.
Part: I
Alternating Current
VSA & MCQ
I. Very Short Answer Questions
Q. What is alternating current (AC)?
Ans: Alternating current is a current that changes magnitude and direction periodically.
Q. What is the expression for AC current?
Ans: I = I₀ sin(ωt).
Q. What is peak current?
Ans: Maximum value of current, I₀.
Q. What is time period of AC?
Ans: Time for one complete cycle, T = 1/f.
Q. What is frequency?
Ans: Number of cycles per second, f.
Q. What is angular frequency?
Ans: ω = 2πf.
Q. What is RMS value of current?
Ans: I_rms = I₀ / √2.
Q. What is RMS voltage?
Ans: V_rms = V₀ / √2.
Q. What is average value of AC over a cycle?
Ans: Zero.
Q. What is reactance?
Ans: Opposition to AC due to inductance or capacitance.
Q. What is inductive reactance?
Ans: X_L = ωL.
Q. What is capacitive reactance?
Ans: X_C = 1 / (ωC).
Q. What is impedance?
Ans: Z = √(R² + (X_L − X_C)²).
Q. What is phase difference?
Ans: Difference in phase between voltage and current.
Q. What is phase in pure resistor?
Ans: Zero.
Q. What is phase in inductor?
Ans: Current lags by 90°.
Q. What is phase in capacitor?
Ans: Current leads by 90°.
Q. What is resonance condition?
Ans: X_L = X_C.
Q. What is resonant frequency?
Ans: f = 1 / (2π√(LC)).
Q. What is power in AC circuit?
Ans: P = V_rms I_rms cosφ.
Q. What is power factor?
Ans: cosφ.
Q. What is wattless current?
Ans: Current with zero power.
Q. What is transformer?
Ans: Device to change AC voltage.
Q. What is step-up transformer?
Ans: Increases voltage.
Q. What is step-down transformer?
Ans: Decreases voltage.
Q. What is efficiency of transformer?
Ans: Ratio of output to input power.
Q. What is eddy current loss?
Ans: Energy loss due to induced currents.
Q. What is hysteresis loss?
Ans: Loss due to magnetization cycle.
Q. What is skin effect?
Ans: Current flows near surface at high frequency.
Q. What is choke coil?
Ans: Inductor used to control current.
II. Multiple Choice Questions
Q. AC changes:
(a) Magnitude only
(b) Direction only
(c) Both
(d) None
Ans: (c)
Q. RMS current is:
(a) I₀
(b) I₀/2
(c) I₀/√2
(d) 2I₀
Ans: (c)
Q. Angular frequency is:
(a) f
(b) 2πf
(c) πf
(d) f/2
Ans: (b)
Q. Inductive reactance is:
(a) ωL
(b) 1/ωC
(c) R
(d) L/C
Ans: (a)
Q. Capacitive reactance is:
(a) ωL
(b) 1/ωC
(c) R
(d) LC
Ans: (b)
Q. At resonance:
(a) X_L > X_C
(b) X_L < X_C
(c) X_L = X_C
(d) Zero current
Ans: (c)
Q. Power factor is:
(a) sinφ
(b) cosφ
(c) tanφ
(d) secφ
Ans: (b)
Q. Transformer works on:
(a) DC
(b) AC
(c) Both
(d) None
Ans: (b)
Q. Wattless current occurs in:
(a) Pure resistor
(b) Pure inductor
(c) Both
(d) None
Ans: (b)
Q. Impedance unit is:
(a) Ohm
(b) Volt
(c) Ampere
(d) Watt
Ans: (a)
Q. Assertion: AC has zero average value. Reason: Positive and negative cancel.
(a) Both true, reason correct
(b) Both true, reason incorrect
(c) Assertion true, reason false
(d) Both false
Ans: (a)
Q. Assertion: RMS gives effective value. Reason: Produces same heating.
(a) Both true, reason correct
(b) Both true, reason incorrect
(c) Assertion true, reason false
(d) Both false
Ans: (a)
Q. Assertion: Inductor opposes AC. Reason: Induced emf resists change.
(a) Both true, reason correct
(b) Both true, reason incorrect
(c) Assertion true, reason false
(d) Both false
Ans: (a)
Q. Assertion: Capacitor blocks DC. Reason: No change in voltage.
(a) Both true, reason correct
(b) Both true, reason incorrect
(c) Assertion true, reason false
(d) Both false
Ans: (a)
Q. Assertion: At resonance impedance is minimum. Reason: X_L = X_C.
(a) Assertion true, reason false
(b) Both true, reason incorrect
(c) Both true, reason correct
(d) Both false
Ans: (c)
Q. Assertion: Power factor is zero in pure inductor. Reason: cos90° = 0.
(a) Both true, reason correct
(b) Both true, reason incorrect
(c) Assertion true, reason false
(d) Both false
Ans: (a)
Q. Assertion: Transformer needs AC. Reason: Flux must change.
(a) Both true, reason incorrect
(b) Both true, reason correct
(c) Assertion true, reason false
(d) Both false
Ans: (b).
