Chapter Exam

Chapter-7 Alternating Current — Online MCQ Test

Q: What is the RMS (root mean square) value of an alternating current with peak value I₀?

Answer: B. I₀/√2 — The RMS value of an AC current is defined as I₀/√2, where I₀ is the peak (maximum) value of the current.

Q: Which of the following is the SI unit of reactance?

Answer: B. Ohm — Reactance (inductive or capacitive) is measured in Ohms (Ω), the same unit as resistance.

Q: A sinusoidal AC voltage is given by V(t) = 230sin(ωt) V. What is its RMS voltage?

Answer: B. 230/√2 V ≈ 163 V — The peak voltage is 230 V, so RMS voltage = 230/√2 ≈ 163 V. The value 230 V used in India is already the RMS value.

Q: In a series RLC circuit, if the inductance is decreased while keeping resistance and capacitance constant, the resonant frequency will:

Answer: B. Increase — Resonant frequency f₀ = 1/(2π√LC) is inversely proportional to √L. Decreasing L increases the resonant frequency.

Q: A resonant LCR circuit has R = 5 Ω, L = 10 mH, and the resonant frequency is 1000 Hz. What is the capacitance?

Answer: A. 2.53 μF — At resonance, f₀ = 1/(2π√LC), so C = 1/(4π²f₀²L) = 1/(4π² × 10⁶ × 0.01) ≈ 2.53 × 10⁻⁶ F = 2.53 μF.

PHYSICS · CLASS 12 SECOND PUC · Karnataka State Board

Practice Chapter-7 Alternating Current with a free chapter-wise online MCQ test for Karnataka State Board CLASS 12 SECOND PUC PHYSICS. This chapter covers: AC circuits - RMS value - reactance - impedance - LCR circuit - resonance - transformer - AC generator. AI-generated questions from basic to board-exam level, with instant results and explanations.

Questions

20m

Time Limit

Attempts Left

10 random questions from this chapter (mixed difficulty)
Questions you've seen before won't repeat until the pool resets
You have 20 minutes — exam auto-submits when time is up
Maximum 3 attempts per chapter
Results and explanations shown immediately after submission

New here? Register free — includes 3 free chapter exams.

Chapter-7 Alternating Current — Important Questions & Answers (FAQ)

Frequently asked questions from Karnataka State Board CLASS 12 SECOND PUC PHYSICS — Chapter-7 Alternating Current, with answers and explanations. These are sample questions; the exam has its own separate question set.

What is the RMS (root mean square) value of an alternating current with peak value I₀?

A. I₀/2
B. I₀/√2 ✓
C. I₀√2
D. 2I₀

Answer: B. I₀/√2
The RMS value of an AC current is defined as I₀/√2, where I₀ is the peak (maximum) value of the current.

Which of the following is the SI unit of reactance?

A. Ampere
B. Ohm ✓
C. Henry
D. Farad

Answer: B. Ohm
Reactance (inductive or capacitive) is measured in Ohms (Ω), the same unit as resistance.

A sinusoidal AC voltage is given by V(t) = 230sin(ωt) V. What is its RMS voltage?

A. 230 V
B. 230/√2 V ≈ 163 V ✓
C. 230√2 V ≈ 325 V
D. 115 V

Answer: B. 230/√2 V ≈ 163 V
The peak voltage is 230 V, so RMS voltage = 230/√2 ≈ 163 V. The value 230 V used in India is already the RMS value.

In a series RLC circuit, if the inductance is decreased while keeping resistance and capacitance constant, the resonant frequency will:

A. Decrease
B. Increase ✓
C. Remain unchanged
D. Become zero

Answer: B. Increase
Resonant frequency f₀ = 1/(2π√LC) is inversely proportional to √L. Decreasing L increases the resonant frequency.

A resonant LCR circuit has R = 5 Ω, L = 10 mH, and the resonant frequency is 1000 Hz. What is the capacitance?

A. 2.53 μF ✓
B. 25.3 μF
C. 0.253 μF
D. 253 μF

Answer: A. 2.53 μF
At resonance, f₀ = 1/(2π√LC), so C = 1/(4π²f₀²L) = 1/(4π² × 10⁶ × 0.01) ≈ 2.53 × 10⁻⁶ F = 2.53 μF.

Choose Your Plan & Start Practising

All plans cover every subject and chapter of your registered grade.

Free

₹0

3 exams · 1 year

Start Free →

Active

₹350

12 exams · 1 year

Get Active →

Pro

₹899

Unlimited exams · 1 year

Get Pro →

Compare all plans in detail →