Online Test — Waves
18 Questions • 15 min • Chapter MCQ
15:00
Question 1 of 18
A wave carries from one place to another:
matter only
energy and momentum
the whole medium
nothing
Explanation: A wave transports energy and momentum through the medium without bulk movement of the medium itself.
Question 2 of 18
Which of the following is a longitudinal wave?
wave on a string
light wave
sound in air
ripple on water surface
Explanation: Sound in air is longitudinal — air particles vibrate parallel to the direction of propagation.
Question 3 of 18
The relation $v=f\lambda$ holds because in one time period the wave advances by:
one amplitude
one wavelength
half a wavelength
two wavelengths
Explanation: The wave moves one wavelength in one period $T$, so $v=\frac{\lambda}{T}=f\lambda$.
Question 4 of 18
The speed of a transverse wave on a string of tension $T$ and mass per unit length $\mu$ is:
$\sqrt{T\mu}$
$\sqrt{\frac{T}{\mu}}$
$\frac{T}{\mu}$
$\sqrt{\frac{\mu}{T}}$
Explanation: Wave speed on a string is $v=\sqrt{\frac{T}{\mu}}$.
Question 5 of 18
A wave of frequency 200 Hz travels at 360 m/s. Its wavelength is:
$0.9\ \text{m}$
$1.8\ \text{m}$
$72\ \text{m}$
$0.56\ \text{m}$
Explanation: $\lambda=\frac{v}{f}=\frac{360}{200}=1.8\ \text{m}$.
Question 6 of 18
In $y=A\sin(\omega t-kx)$, the wave speed equals:
$\omega k$
$\frac{\omega}{k}$
$\frac{k}{\omega}$
$Ak$
Explanation: Wave speed $v=\frac{\omega}{k}=f\lambda$.
Question 7 of 18
If the tension in a string is made 9 times, the wave speed becomes:
3 times
9 times
$\frac{1}{3}$ times
unchanged
Explanation: $v\propto\sqrt{T}$, so $\sqrt{9}=3$; the speed triples.
Question 8 of 18
The principle of superposition states that the resultant displacement is the:
product of the displacements
vector sum of the displacements
average of the speeds
larger of the two displacements
Explanation: Overlapping waves add by vector sum of displacements.
Question 9 of 18
Constructive interference occurs when the path difference is:
$n\lambda$
$(2n+1)\frac{\lambda}{2}$
$\frac{\lambda}{4}$
$\frac{n\lambda}{3}$
Explanation: In-phase waves (path difference a whole number of wavelengths, $n\lambda$) reinforce.
Question 10 of 18
In a standing wave, points of zero displacement are called:
antinodes
nodes
crests
loops
Explanation: Nodes are points that remain permanently at rest in a standing wave.
Question 11 of 18
The distance between a node and the next antinode is:
$\lambda$
$\frac{\lambda}{2}$
$\frac{\lambda}{4}$
$2\lambda$
Explanation: Node-to-antinode spacing is a quarter wavelength, $\frac{\lambda}{4}$.
Question 12 of 18
A pipe closed at one end produces:
all harmonics
only even harmonics
only odd harmonics
no harmonics
Explanation: A closed pipe (node at closed end, antinode at open end) gives only odd harmonics, $f_n=\frac{nv}{4L}$, $n$ odd.
Question 13 of 18
The fundamental frequency of an open pipe of length $L$ is:
$\frac{v}{4L}$
$\frac{v}{2L}$
$\frac{v}{L}$
$\frac{2v}{L}$
Explanation: An open pipe has antinodes at both ends, $L=\frac{\lambda}{2}$, so $f_1=\frac{v}{2L}$.
Question 14 of 18
Two forks of 256 Hz and 260 Hz sounded together give beats per second:
2
4
8
516
Explanation: Beat frequency $=|260-256|=4\ \text{Hz}$.
Question 15 of 18
Beats are used mainly to:
measure the speed of light
tune musical instruments
produce standing waves
increase wave speed
Explanation: Beats vanish when two frequencies match, so they let a musician tune an instrument precisely.
Question 16 of 18
The Doppler effect is the apparent change in the sound's:
amplitude
frequency
speed in the medium
wavelength only
Explanation: Relative motion of source and observer changes the observed frequency (pitch).
Question 17 of 18
A source of 500 Hz approaches a stationary observer at 33 m/s ($v=330$ m/s). The observed frequency is about:
$450\ \text{Hz}$
$500\ \text{Hz}$
$556\ \text{Hz}$
$330\ \text{Hz}$
Explanation: $f'=500\frac{330}{330-33}=500\frac{330}{297}\approx556\ \text{Hz}$.
Question 18 of 18
When a sound source moves away from a stationary observer, the observed pitch:
rises
falls
is unchanged
becomes zero
Explanation: Receding source: $f'=f\frac{v}{v+v_s}
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