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Waves — NEET & JEE MCQs with answers
Waves are patterns of disturbance that move through a medium without the actual transfer or flow of matter as a whole, carrying energy from one point to another; electromagnetic waves need no medium and can travel through vacuum. This chapter covers transverse and longitudinal waves, the displacement relation of a progressive harmonic wave, the speed of a travelling wave, the principle of superposition, reflection of waves with standing waves and normal modes, and beats.
Topics in this chapter
- 14.1 Introduction
- 14.2 Transverse and Longitudinal Waves
- 14.3 Displacement Relation in a Progressive Wave
- 14.4 The Speed of a Travelling Wave
- 14.5 The Principle of Superposition of Waves
- 14.6 Reflection of Waves and Standing Waves
- 14.7 Beats
Free practice questions
At a point, wave 1 gives displacement $+0.8\,\text{cm}$ and wave 2 gives $-0.3\,\text{cm}$ at the same instant. The net displacement is
- A. $1.1\,\text{cm}$
- B. $0.24\,\text{cm}$
- C. $0.5\,\text{cm}$
- D. $0.85\,\text{cm}$
Show answer
Answer: C — Net $= +0.8 - 0.3 = +0.5\,\text{cm}$ (algebraic sum).
NCERT Class 11 Physics · Ch 14 · 14.5 The Principle of Superposition of Waves
A wave has $k=2\pi\ \text{rad m}^{-1}$. Its wavelength is:
- A. 2 m
- B. 0.5 m
- C. 1 m
- D. $2\pi$ m
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Answer: C — $\lambda=2\pi/k=2\pi/2\pi=1\ \text{m}$.
NCERT Class 11 Physics · Ch 14 · 14.3 Mathematical Description of a Wave
In a pipe open at both ends, which harmonics are present?
- A. only odd harmonics
- B. all harmonics
- C. only even harmonics
- D. only the fundamental
Show answer
Answer: B — An air column open at both ends generates all harmonics (1st, 2nd, 3rd, ...).
NCERT Class 11 Physics · Ch 14 · 14.6 Reflection of Waves and Standing Waves
A certain elastic medium can sustain compressive strain but not shearing stress. Which waves can it support?
- A. Neither type of wave
- B. Only transverse waves
- C. Only longitudinal waves
- D. Both transverse and longitudinal waves
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Answer: C — NCERT: a medium that sustains compressive strain but not shearing stress (a fluid) supports only longitudinal waves; transverse waves need a medium that sustains shearing stress.
NCERT Class 11 Physics Ch 14
Waves are important to communication chiefly because they:
- A. remain confined to a single point
- B. carry information from one point to another
- C. transport large amounts of matter over long distances
- D. destroy the medium as they pass through it
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Answer: B — NCERT states that all our communications essentially depend on transmission of signals through waves; waves transport the pattern of disturbance, which carries information, from one point to another.
NCERT Class 11 Physics Ch 14
The transverse wave speed on a string with $T = 100\ \text{N}$ and $\mu = 0.04\ \text{kg/m}$ is:
- A. $50\ \text{m/s}$
- B. $100\ \text{m/s}$
- C. $25\ \text{m/s}$
- D. $2500\ \text{m/s}$
Show answer
Answer: A — $v = \sqrt{T/\mu} = \sqrt{100/0.04} = \sqrt{2500} = 50\ \text{m/s}$.
NCERT Class 11 Physics · Ch 14 · 14.4 The Speed of a Travelling Wave
A fork of frequency $200\,\text{Hz}$ produces $4$ beats per second with a sonometer wire. The wire's frequency is found to decrease as its length is increased. To make the beats zero by changing length, the wire (currently $1.00\,\text{m}$, higher than fork) must be lengthened to:
- A. 0.96 m
- B. 1.02 m
- C. 1.04 m
- D. 0.98 m
Show answer
Answer: B — Wire frequency $=204\,\text{Hz}$ at $1.00\,\text{m}$. $\nu\propto1/L\Rightarrow L'=1.00\times204/200=1.02\,\text{m}$.
NCERT Class 11 Physics · Ch 14 · 14.7 Beats
For constructive interference of two equal-amplitude waves, the phase difference must be
- A. $\phi = n\pi/3$
- B. $\phi = 2n\pi$
- C. $\phi = (2n+1)\pi/2$
- D. $\phi = (2n+1)\pi$
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Answer: B — Constructive interference occurs at $\phi = 0, 2\pi, 4\pi, \ldots = 2n\pi$ (integer $n$), where $\cos(\phi/2) = \pm 1$ and amplitude is maximum $2a$.
NCERT Class 11 Physics · Ch 14 · 14.5 The Principle of Superposition of Waves
A pipe of length $0.5\,\text{m}$ is open at both ends. With sound speed $300\,\text{m/s}$, the fundamental frequency of the air column is
- A. 600 Hz
- B. 450 Hz
- C. 150 Hz
- D. 300 Hz
Show answer
Answer: D — Open pipe fundamental: $\nu_1=\dfrac{v}{2L}=\dfrac{300}{2\times 0.5}=300\,\text{Hz}$.
NCERT Class 11 Physics · Ch 14 · 14.6 Reflection of Waves and Standing Waves
The angular wave number $k$ represents $2\pi$ times the number of waves that can be accommodated:
- A. per unit length
- B. per unit time
- C. per period
- D. per second
Show answer
Answer: A — NCERT footnote: $k$ represents $2\pi$ times the number of waves (total phase difference) per unit length.
NCERT Class 11 Physics · Ch 14 · 14.3 Mathematical Description of a Wave
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