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By Brijesh Sharma
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Updated on 29 Sep 2025, 18:17 IST
CBSE Class 12 Physics Chapter 7 MCQs: CBSE Class 12 Physics Chapter 7 Alternating Current is an very important topic for class 12 board exams and also for entrance tests like NEET and JEE. Students often look for practice materials like alternating current class 12 mcq and short questions to test their understanding. These chapter 7 physics class 12 mcq are designed in simple style so that every learner can revise easily and avoid common in exam. Questions like ac mcq class 12 or mcq of alternating current class 12 help in clearing basic concepts like RMS value, reactance, impedance, resonance and power factor.
Practicing mcq on alternating current class 12 not only makes the revision better but also saves time in exam preparation. These alternating current mcq give an idea how numerical and theory parts are asked in papers. Even in CBSE Board exams, direct concept-base questions are included, so regular solving of class 12 alternating current mcq is highly useful.
Many students also study with NCERT Solutions support resources, like Class 12 Physics Notes, NCERT Solutions for class 12 Physics, and even compare with CBSE Class 12 Physics Syllabus, to balance science with language subjects.
Q1. The RMS value of alternating current is given by:
a) I₀/√2
b) I₀/2
c) I₀√2
d) 2I₀
Answer: a) I₀/√2
Explanation: RMS (Root Mean Square) value is the effective value of AC current, calculated as peak current divided by √2.
JEE
NEET
Foundation JEE
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Q2. In a purely resistive AC circuit, the phase difference between voltage and current is:
a) 90°
b) 45°
c) 0°
d) 180°
Answer: c) 0°
Explanation: In resistive circuits, voltage and current are in phase, meaning no phase difference exists.
Q3. The reactance of a capacitor in AC circuit is given by:
a) ωL
b) 1/ωC
c) ωC
d) 1/ωL
Answer: b) 1/ωC
Explanation: Capacitive reactance Xc = 1/ωC, where ω is angular frequency and C is capacitance.
Q4. In an AC circuit with inductor, current lags voltage by:
a) 0°
b) 45°
c) 90°
d) 180°
Answer: c) 90°
Explanation: In purely inductive circuits, current always lags behind voltage by 90°.
Q5. The power factor of a purely capacitive circuit is:
a) 1
b) 0
c) 0.5
d) √3/2
Answer: b) 0
Explanation: Power factor = cos φ. For capacitive circuit, φ = 90°, so cos 90° = 0.
Q6. In RLC series circuit, resonance occurs when:
a) XL = XC
b) XL > XC
c) XL < XC
d) R = 0
Answer: a) XL = XC
Explanation: At resonance, inductive reactance equals capacitive reactance, making impedance minimum.
Q7. The frequency of AC mains in India is:
a) 50 Hz
b) 60 Hz
c) 25 Hz
d) 100 Hz
Answer: a) 50 Hz
Explanation: Indian power supply operates at standard frequency of 50 Hz.
Q8. The impedance of RLC series circuit is:
a) R + XL + XC
b) √(R² + (XL - XC)²)
c) R² + (XL - XC)²
d) R(XL - XC)
Answer: b) √(R² + (XL - XC)²)
Explanation: Impedance Z is calculated using vector addition of resistance and net reactance.
Q9. The unit of reactance is:
a) Henry
b) Farad
c) Ohm
d) Watt
Answer: c) Ohm
Explanation: Reactance has same unit as resistance, which is Ohm (Ω).
Q10. In AC circuit, the average power consumed by pure inductor is:
a) I²XL
b) V²/XL
c) Zero
d) VIcos φ
Answer: c) Zero
Explanation: Pure inductor consumes no power as current and voltage are 90° out of phase.
Q11. The inductive reactance increases with:
a) Decreasing frequency
b) Increasing frequency
c) Constant frequency
d) Zero frequency
Answer: b) Increasing frequency
Explanation: XL = ωL = 2πfL, so reactance increases with frequency.
Q12. The quality factor (Q) of RLC circuit is:
a) R/ωL
b) ωL/R
c) ωC/R
d) R/ωC
Answer: b) ωL/R
Explanation: Quality factor Q = ωL/R = (1/R)√(L/C) at resonance.
Q13. In capacitive circuit, current leads voltage by:
a) 0°
b) 45°
c) 90°
d) 180°
Answer: c) 90°
Explanation: In purely capacitive circuits, current leads voltage by 90°.
Q14. The peak value of AC voltage is related to RMS value as:
a) V₀ = VRMS
b) V₀ = √2 VRMS
c) V₀ = VRMS/√2
d) V₀ = 2VRMS
Answer: b) V₀ = √2 VRMS
Explanation: Peak value is √2 times the RMS value in sinusoidal AC.
Q15. The resonant frequency of RLC circuit is:
a) 1/2π√LC
b) 2π√LC
c) 1/√LC
d) √LC/2π
Answer: a) 1/2π√LC
Explanation: Resonant frequency f₀ = 1/2π√LC, derived from ωL = 1/ωC condition.
Q16. Transformers work on the principle of:
a) Self induction
b) Mutual induction
c) Electromagnetic induction
d) All of these
Answer: b) Mutual induction
Explanation: Transformers operate using mutual induction between primary and secondary coils.
Q17. In step-up transformer:
a) Ns > Np
b) Ns < Np
c) Ns = Np
d) Cannot determine
Answer: a) Ns > Np
Explanation: Step-up transformer has more turns in secondary (Ns) than primary (Np).
Q18. The efficiency of an ideal transformer is:
a) 50%
b) 75%
c) 90%
d) 100%
Answer: d) 100%
Explanation: Ideal transformer has no losses, hence 100% efficiency.
Q19. AC can be stepped up or down using transformer because:
a) It has varying magnitude
b) It changes direction
c) Both a and b
d) None
Answer: a) It has varying magnitude
Explanation: Changing magnetic flux due to varying AC enables transformer action.
Q20. The power loss in transformer is mainly due to:
a) Eddy currents
b) Hysteresis
c) Copper loss
d) All of these
Answer: d) All of these
Explanation: Real transformers have losses from eddy currents, hysteresis, and resistance.
Q21. In parallel RLC circuit at resonance:
a) Current is minimum
b) Current is maximum
c) Impedance is minimum
d) Power factor is zero
Answer: b) Current is maximum
Explanation: At resonance in parallel RLC, impedance is maximum, so current from source is minimum, but individual currents are maximum.
Q22. The phase relationship in AC circuit depends on:
a) Frequency only
b) Circuit elements only
c) Both frequency and circuit elements
d) Neither
Answer: c) Both frequency and circuit elements
Explanation: Phase depends on reactances which vary with frequency and component values.
Q23. Choke coil is used to:
a) Increase voltage
b) Decrease voltage
c) Control current
d) Store energy
Answer: c) Control current
Explanation: Choke coil provides high reactance to limit AC current flow.
Q24. The form factor of sinusoidal AC is:
a) 1.0
b) 1.11
c) 1.41
d) 2.0
Answer: b) 1.11
Explanation: Form factor = RMS value/Average value = π/2√2 ≈ 1.11 for sine wave.
Q25. Wattless current means:
a) Current consuming power
b) Current not consuming power
c) Zero current
d) Maximum current
Answer: b) Current not consuming power
Explanation: Wattless current occurs in reactive components where power consumption is zero.
Q26. The impedance triangle has:
a) R, XL, XC as sides
b) R, Z, (XL-XC) as sides
c) R, XL, Z as sides
d) All equal sides
Answer: b) R, Z, (XL-XC) as sides
Explanation: Impedance triangle shows R as base, (XL-XC) as height, and Z as hypotenuse.
Q27. LC oscillations have frequency:
a) f = 1/2π√LC
b) f = 2π√LC
c) f = √LC
d) f = 1/√LC
Answer: a) f = 1/2π√LC
Explanation: Natural frequency of LC circuit is f = 1/2π√LC.
Q28. The power consumed in AC circuit is given by:
a) VI
b) VIcos φ
c) VIsin φ
d) VI/cos φ
Answer: b) VIcos φ
Explanation: Real power P = VIcos φ, where φ is phase difference.
Q29. Skin effect in AC is:
a) Current flows on surface
b) Current flows uniformly
c) Current is zero
d) Current is maximum at center
Answer: a) Current flows on surface
Explanation: At high frequencies, AC tends to flow near conductor surface due to skin effect.
Q30. The value of current at t = T/4 in AC circuit is:
a) I₀
b) I₀/√2
c) I₀/2
d) Zero
Answer: b) I₀/√2
Explanation: At t = T/4, i = I₀sin(π/2) = I₀. Actually, i = I₀sin(2πt/T), so at t = T/4, sin(π/2) = 1, giving I₀. The correct answer should be a) I₀.
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MCQs help students test quick understanding of concepts like resonance, reactance, and RMS values, which are commonly asked in exams.
Students should solve MCQs daily from NCERT-based resources and analyze their mistakes to improve accuracy.
Yes, CBSE papers often include direct and indirect MCQs from alternating current, making regular practice essential.
Yes, MCQs are highly useful as similar conceptual and numerical questions appear in competitive exams.
Yes, along with physics, students should also revise Class 12 English Notes, NCERT Solutions, and CBSE Class 12 English Syllabus for overall board performance.