Oscillations — Class 11 MCQs with Answers

Oscillations — important questions & MCQs with answers (Class 11 Physics)

13 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 53 are timed and scored when you sign in.

1. Q1Easy

   In SHM, restoring force is proportional to:

   A.Velocity

   B.Displacement (and opposite in direction)✓ Correct

   C.Acceleration squared

   D.Mass

   Answer: B. Displacement (and opposite in direction)

   Explanation: Newton's SHM law states F = −kx: restoring force is proportional to displacement and directed opposite to it, unlike a velocity-proportional damping force which is the tempting but wrong distractor here.

2. Q2Easy

   Period of spring-mass system: T = ?

   A.2π√(k/m)

   B.2π√(m/k)✓ Correct

   C.2π·m·k

   D.Variable

   Answer: B. 2π√(m/k)

   Explanation: For a spring-mass oscillator, T = 2π√(m/k): a larger mass m increases the period while a stiffer spring (larger k) decreases it — inverting the ratio to √(k/m) reverses both trends.

3. Q3Easy

   Period of simple pendulum (small angle): T = ?

   A.√(Lg)

   B.2π√(g/L)

   C.Lg

   D.2π√(L/g)✓ Correct

   Answer: D. 2π√(L/g)

   Explanation: Small-angle pendulum period is T = 2π√(L/g): a longer string L increases T while stronger gravity g shortens it — flipping the ratio to √(g/L) gets both dependences backwards.

4. Q4Easy

   Damped oscillations have:

   A.Constant

   B.Decreasing amplitude over time✓ Correct

   C.Increasing

   D.Variable

   Answer: B. Decreasing amplitude over time

   Explanation: Damped oscillations lose mechanical energy to resistance each cycle, so amplitude shrinks progressively over time — treating amplitude as staying constant ignores this energy dissipation entirely.

5. Q5Easy

   Resonance occurs when:

   A.Driving frequency = natural frequency✓ Correct

   B.Damping high

   C.Random

   D.Mass = stiffness

   Answer: A. Driving frequency = natural frequency

   Explanation: Resonance happens when the driving frequency matches the system's own natural frequency, letting energy build up each cycle and amplitude grow sharply — high damping actually suppresses this peak rather than causing it.

6. Q6Medium

   Period of mass m on spring k:

   A.2π√(k/m)

   B.2π√(m/k)✓ Correct

   C.2π(m/k)

   D.√(km)

   Answer: B. 2π√(m/k)

   Explanation: For a spring–mass system, T = 2π√(m/k): heavier mass (m in numerator) oscillates slower. Swapping to √(k/m) is the tempting mix-up that wrongly makes a stiffer spring swing slower.

7. Q7Medium

   Spring k = 100 N/m, m = 0.25 kg. Period:

   A.Cannot compute

   B.2π/10

   C.π

   D.π/10 s✓ Correct

   Answer: D. π/10 s

   Explanation: Period is T = 2π√(m/k) = 2π√(0.25 kg / 100 N·m⁻¹) = 2π√0.0025 = 2π(0.05) = π/10 s — forgetting to take the square root before multiplying by 2π gives a badly oversized answer.

8. Q8Medium

   Simple pendulum of length 1 m on Earth (g = 9.8):

   A.1 s

   B.≈ 2.007 s ≈ 2 s✓ Correct

   C.4 s

   D.Cannot compute

   Answer: B. ≈ 2.007 s ≈ 2 s

   Explanation: Period is T = 2π√(L/g) = 2π√(1 m / 9.8 m/s²) ≈ 2π(0.319) ≈ 2.007 s — using g = 10 m/s² instead of the stated 9.8 shifts the answer slightly, so match g to what the question gives.

9. Q9Medium

   Amplitude in damped oscillation: A(t) = ?

   A.Variable

   B.A₀

   C.Constant

   D.A₀ e^(−γt/2)✓ Correct

   Answer: D. A₀ e^(−γt/2)

   Explanation: Damping removes energy in proportion to the current amplitude, giving exponential decay A(t) = A₀e^(−γt/2) — treating A as staying at its initial value A₀ ignores this ongoing energy loss entirely.

10. Q10Medium

    Q-factor (quality factor) measures:

    A.Energy

    B.Sharpness of resonance✓ Correct

    C.Frequency

    D.Cannot define

    Answer: B. Sharpness of resonance

    Explanation: The quality factor Q measures how sharp and tall a resonance peak is: high Q means low damping and a narrow peak — Q is a dimensionless ratio, not itself an energy or a frequency value.

11. Q11Hard

    If x = A sin(ωt), then velocity v =

    A.−A sin(ωt)

    B.Aω cos(ωt)✓ Correct

    C.Aω² sin(ωt)

    D.0

    Answer: B. Aω cos(ωt)

    Explanation: Differentiating x = A sin(ωt) gives v = dx/dt = Aω cos(ωt) — velocity leads displacement by 90°. Forgetting the ω factor, as in plain −A sin(ωt), is the tempting but dimensionally wrong distractor.

12. Q12Hard

    Spring with k. Period halved when mass changed. New mass:

    A.4m

    B.m/2

    C.m/4✓ Correct

    D.Cannot determine

    Answer: C. m/4

    Explanation: Since T = 2π√(m/k) ∝ √m, halving the period requires (T/2)/T = √(m_new/m) = 1/2, so m_new/m = 1/4 — mistakenly halving the mass directly to m/2 ignores that period depends on the square root of mass.

13. Q13Hard

    A simple pendulum with period T₀ at the Earth's surface is taken to altitude h above it (h ≪ R). Its new period is:

    A.T₀(1 + h/R)✓ Correct

    B.T₀(1 − h/R)

    C.T₀√(1 + h/R)

    D.T₀(1 + h/R)²

    Answer: A. T₀(1 + h/R)

    Explanation: At altitude, g_h = GM/(R+h)², so T = 2π√(L/g_h) scales as (R+h): T_h = T₀(R+h)/R = T₀(1 + h/R). Answering T₀(1 − h/R) has the pendulum speeding up, but weaker gravity always makes it swing SLOWER.

Oscillations — FAQs

More Class 11 Physics chapters

• 01Physical World
• 02Units and Measurements
• 03Motion in a Straight Line
• 04Motion in a Plane
• 05Laws of Motion
• 06Work, Energy and Power

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• Class 11 Biology chapters
• Class 11 Chemistry chapters
• Class 11 Computer Science chapters
• Class 11 English chapters
• Class 11 Mathematics chapters