Waves — Class 11 MCQs with Answers

Waves — 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

   Light is a ___ wave.

   A.Transverse (electromagnetic)✓ Correct

   B.Longitudinal

   C.Mechanical

   D.Stationary only

   Answer: A. Transverse (electromagnetic)

   Explanation: Light is an electromagnetic wave: E and B oscillate perpendicular to the direction of travel, making it transverse. It needs no medium, unlike mechanical waves such as sound — that's the tempting mix-up here.

2. Q2Easy

   Transverse wave: particle motion is:

   A.Parallel

   B.Perpendicular to wave propagation✓ Correct

   C.Random

   D.No motion

   Answer: B. Perpendicular to wave propagation

   Explanation: In a transverse wave, particles oscillate perpendicular to the direction the wave travels — like a string moved up and down while the wave moves sideways. Parallel motion instead describes a longitudinal wave, the usual mix-up.

3. Q3Easy

   Wavelength λ is:

   A.Amplitude

   B.Time period

   C.Frequency

   D.Distance between two consecutive crests/compressions✓ Correct

   Answer: D. Distance between two consecutive crests/compressions

   Explanation: Wavelength λ is the distance between two consecutive crests (or compressions), one full spatial cycle of the wave. Confusing it with amplitude, the maximum displacement from equilibrium, is the common slip.

4. Q4Easy

   Speed of sound in air ≈

   A.343 m/s✓ Correct

   B.100

   C.1000

   D.3 × 10⁸

   Answer: A. 343 m/s

   Explanation: Speed of sound in air at room temperature (≈20°C) is about 343 m/s, far slower than light's 3×10⁸ m/s. Confusing the two — or picking 1000 m/s — ignores that sound needs a medium and moves much slower.

5. Q5Easy

   Speed of light in vacuum:

   A.3 × 10⁶

   B.3 × 10⁸ m/s✓ Correct

   C.3 × 10¹⁰

   D.Cannot say

   Answer: B. 3 × 10⁸ m/s

   Explanation: Speed of light in vacuum is c = 3 × 10⁸ m/s, a universal constant used throughout electromagnetism. Picking 3 × 10⁶ or 3 × 10¹⁰ m/s is off by a factor of 100 — a common power-of-ten slip.

6. Q6Medium

   Wave with f = 100 Hz, λ = 5 m. Speed:

   A.105

   B.500 m/s✓ Correct

   C.20

   D.Cannot compute

   Answer: B. 500 m/s

   Explanation: Wave speed v = fλ = 100 Hz × 5 m = 500 m/s. Picking 105 m/s (adding instead of multiplying) or 20 m/s (dividing) confuses the multiplicative relation between frequency and wavelength.

7. Q7Medium

   Speed of sound in gas: v = ?

   A.√(γRT/M)

   B.√(γP/ρ)

   C.Both✓ Correct

   D.Variable

   Answer: C. Both

   Explanation: Speed of sound in a gas can be written either as v = √(γRT/M) using temperature, or v = √(γP/ρ) using pressure and density — both are algebraically equivalent via the ideal gas law. Picking only one ignores this equivalence.

8. Q8Medium

   Wave with k = 2 rad/m. λ =

   A.π m✓ Correct

   B.2π

   C.π/2

   D.2

   Answer: A. π m

   Explanation: Wavelength from wave number is λ = 2π/k = 2π/2 = π m ≈ 3.14 m. Picking 2π m instead skips dividing by k, mixing up k with 1/k.

9. Q9Medium

   Wave speed v =

   A.f / λ

   B.f × λ✓ Correct

   C.f + λ

   D.f² × λ

   Answer: B. f × λ

   Explanation: Wave speed follows v = f × λ, the fundamental relation linking frequency and wavelength. Writing v = f/λ or f + λ instead confuses the multiplicative relationship — those are the tempting but wrong forms.

10. Q10Medium

    Speed of wave on stretched string: v = ?

    A.√T·μ

    B.√(T/μ) where μ is mass per unit length✓ Correct

    C.T/μ

    D.Cannot define

    Answer: B. √(T/μ) where μ is mass per unit length

    Explanation: Transverse wave speed on a stretched string is v = √(T/μ), tension divided by mass per unit length, under a square root. Writing v = √(T·μ) flips the ratio, giving the wrong dependence on both quantities.

11. Q11Hard

    Stationary waves form by superposition of:

    A.Different frequencies

    B.Two waves of same frequency travelling in opposite directions✓ Correct

    C.Light only

    D.Random pulses

    Answer: B. Two waves of same frequency travelling in opposite directions

    Explanation: Stationary (standing) waves arise when two waves of the same frequency and amplitude travel in opposite directions and superpose, creating fixed nodes and antinodes. Different frequencies would produce beats, not a standing pattern.

12. Q12Hard

    A wave equation y = 0.05 sin(100t − 10x). Speed of wave:

    A.Cannot determine

    B.100

    C.0.05

    D.10 m/s✓ Correct

    Answer: D. 10 m/s

    Explanation: Comparing y = 0.05 sin(100t − 10x) to the standard form A sin(ωt − kx) gives ω = 100 rad/s and k = 10 rad/m, so v = ω/k = 100/10 = 10 m/s. Picking 100 m/s mistakes ω alone for the wave speed.

13. Q13Hard

    Speed of sound in air at 27°C (M = 29 g/mol, γ = 1.4):

    A.≈ 348 m/s✓ Correct

    B.100

    C.1000

    D.Cannot compute

    Answer: A. ≈ 348 m/s

    Explanation: Speed of sound in air at 27°C = 300 K: v = √(γRT/M) = √(1.4 × 8.314 × 300 / 0.029) ≈ 348 m/s. Forgetting to convert molar mass from 29 g/mol to 0.029 kg/mol would badly distort the result — that's the trap.

Waves — 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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