MCQ

MCQ 511 Mark

Doppler shift in frequency does not depend upon …….

A
the actual frequency of the wave
✓
the velocity of the source from the listener.
C
the velocity of the source.
D
the velocity of the observer.

Answer

Correct option: B.

the velocity of the source from the listener.

the velocity of the source from the listener

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MCQ 521 Mark

The ratio of the velocity of sound in a monatomic gas to that in a triatomic gas having same molar mass, under similar conditions of temperature and pressure, is ………

✓
1.12
B
1.25
C
1.50
D
1.6

Answer

Correct option: A.

1.12

1.12
Hint :
$v=\sqrt{\frac{\gamma RT }{ M }} \Rightarrow \sqrt{\frac{\gamma_{\text {mono }}}{\gamma_{\text {tri }}}}=\sqrt{\frac{(5 / 3)}{(4 / 3)}}=\sqrt{1.25}=1.12$

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MCQ 531 Mark

Red shift is an illustration of ……….

A
low temperature emission
B
high frequency absorption
✓
Doppler effect
D
Same unknown Phenomenon.

Answer

Correct option: C.

Doppler effect

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MCQ 541 Mark

The equation of a sound wave is y = 0.0015 sin (62.8x + 316t). Find the wave length of the above ……

A
0.2 units
B
0.3 units
✓
0.1 units
D
0.15 unit

Answer

Correct option: C.

0.1 units

0.1 units
Hint :
$k=62.8$ units ; $\lambda=\frac{2 \pi}{k}=\frac{2 \times 3.14}{62.8}=0.1$ units

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MCQ 551 Mark

When a wave goes from one medium to another, there is a change in

A
velocity
B
amplitude
C
wavelength
✓
all the above

Answer

Correct option: D.

all the above

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MCQ 561 Mark

When sound waves travel from air to water, which of these remains constant?

A
velocity
B
wavelength
✓
frequency
D
all the above

Answer

Correct option: C.

frequency

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MCQ 571 Mark

The velocity of sound in a gas depends on ….

A
Wavelength only
✓
density and elasticity of gas
C
intensity only
D
amplitude and frequency

Answer

Correct option: B.

density and elasticity of gas

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MCQ 581 Mark

Ultrasonic waves can be detected by ……

A
telephone
B
Hebb’s method
✓
Kundt’s tube
D
Quincke’s tube

Answer

Correct option: C.

Kundt’s tube

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MCQ 591 Mark

If $v_a, v_h$, and $v_m$ are the speeds of sound in air, hydrogen and a metal at the same temperature, then .........

A
$v_h>v_a>v_m$
✓
$v_m>v_h>v_a$
C
$v_h>v_m>v_a$
D
$v_a>v_h>v_m$

Answer

Correct option: B.

$v_m>v_h>v_a$

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MCQ 601 Mark

The speed of sound in oxygen is 332 m/s at STP. The speed of sound in hydrogen at STP will be ……..

A
53/2 m/s
B
2546 m/s
✓
1328 m/s
D
664 m/s

Answer

Correct option: C.

1328 m/s

1328 m/s
Hint :
$v=\sqrt{\frac{\gamma RT }{ M }}$ $\gamma$ is same for both the gases, so, $\frac{v_{ H _2}}{v_{ O _2}}=\sqrt{\frac{ M _{ O _2}}{ M _{ H _2}}}=\sqrt{\frac{32}{2}}=4$ $\Rightarrow f_{ H _2}=4 \times 332=1328 m / s$

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MCQ 611 Mark

When sound waves travel from air to water, which of the following remains constant?

A
velocity
✓
frequency
C
wavelength
D
all of these

Answer

Correct option: B.

frequency

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MCQ 621 Mark

The equation of a transverse wave is given by y = 10 sin{π(0.01x – 2t)} where y and x are in cm and t is in seconds. Its frequency is …….

A
$10 s ^{-1}$
B
$2 s ^{-1}$
✓
$1 s ^{-1}$
D
$0.01 s ^{-1}$

Answer

Correct option: C.

$1 s ^{-1}$

$1 s ^{-1}$
Hint:
Comparing with the standard equation $y=A \sin (k x-\omega t)$,
We have
$
\omega=2 \pi
$
Therefore, Frequency $f=\frac{2 \pi}{\omega}=1 s ^{-1}$

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MCQ 631 Mark

The temperature at which the speed of sound in air becomes double its value at 27°C is …….

A
54°C
B
327°C
✓
927°C
D
-123°C

Answer

Correct option: C.

927°C

927°C
Hint :
$\frac{v_2}{v_1}=\sqrt{\frac{273+t_2}{273+t_1}} \Rightarrow(2)^2=\frac{273+t_2}{273+27} \Rightarrow t_2=927^{\circ} C$

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MCQ 641 Mark

The frequency of a radar is 780 MHz. When it is reflected from an approaching aeroplane the opponent frequency is more than the actual frequency by 2.6 kHz. The speed of the aeroplane is ……

A
0.25 km/s
✓
0.5 km/s
C
1.0 km/s
D
2.0 km/s

Answer

Correct option: B.

0.5 km/s

0.5 km/s $\begin{aligned} \text { Hint: } \quad v^{\prime}=\frac{c+f}{c-f} v \Rightarrow v^{\prime}-v=\left[\frac{c+f}{c-f}-1\right] v \quad[v=c] \\ \Rightarrow \Delta v=\frac{2 v f}{c-f} \approx \frac{2 v f}{c} \Rightarrow v=\frac{2 \Delta v}{2 v}=\frac{3 \times 10^8 \times 2.6 \times 10^3}{2 \times 780 \times 10^6}=0.5 \times 10^3 m / s \end{aligned}$

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MCQ 651 Mark

The apparent wavelength of the light from a star, moving away from the earth, is 0.01% more than its real wave length. The speed of the star with respect to the earth is ……

A
10 km/s
B
15 km/s
✓
30 km/s
D
60 km/s

Answer

Correct option: C.

30 km/s

30 km/s
Hint :
$\frac{v_r}{c}=\frac{\Delta \lambda}{\lambda}$ or $v_r=\frac{0.01}{100} \times 3 \times 10^8=3 \times 10^4 m / s =30 km / s$

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MCQ 661 Mark

When a source of sound is in motion towards a stationary observer, the effect observed is

A
increase in the velocity of sound only
B
decrease in the velocity of sound only
✓
increase in frequency of sound only
D
increase in both the velocity and the frequency of sound

Answer

Correct option: C.

increase in frequency of sound only

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MCQ 671 Mark

If the amplitude of sound is doubled and the frequency reduced to one-fourth, the intensity will ………

A
increase by a factor of 2
B
decrease by a factor of 2
✓
decrease by a factor of 4
D
remain unchanged

Answer

Correct option: C.

decrease by a factor of 4

decrease by a factor of 4
Hint: $I \propto \omega^2 A^2$
$
\Rightarrow \frac{ I ^{\prime}}{ I }=\left(\frac{\omega^{\prime}}{\omega}\right)^2\left(\frac{ A ^{\prime}}{ A }\right)^2=\left(\frac{1}{4}\right)^2(2)^2=\frac{1}{4}
$

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MCQ 681 Mark

With the propagation of a longitudinal wave through a material medium, the quantities transferred in the direction of propagation are ……..

A
energy, momentum and mass
✓
energy and momentum
C
energy and mass
D
energy

Answer

Correct option: B.

energy and momentum

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MCQ 691 Mark

If v0 and v denote the sound velocity and the rms velocity of the molecules in a gas, then ……..

A
$v_0=v(3 l \gamma)^{1 / 2}$
B
$v_0=0$
✓
$v_0=v(\gamma \backslash 3)^{1 / 2}$
D
$v_0$ and $v$ are not related

Answer

Correct option: C.

$v_0=v(\gamma \backslash 3)^{1 / 2}$

$v_0=v(\gamma \mid 3)^{1 / 2}$
Hint :
$\quad v_0=\sqrt{\frac{\gamma RT }{ M }} ; v=\sqrt{\frac{3 RT }{ M }} \Rightarrow \frac{v_o}{v}=\sqrt{\frac{\gamma}{3}} \Rightarrow v_0=v\left(\frac{\gamma}{2}\right)^{\frac{1}{2}}$

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MCQ 701 Mark

A longitudinal wave is described by the equation y = y0 sin 2π (ft – x/λ). The maximum particle velocity is equal to four times the wave velocity if ……..

A
$\lambda=\pi y_0 / 4$
✓
$\lambda=\pi y_0 / 2$
C
$\lambda=4 \pi y_0$
D
$\lambda=2 \pi y_0$

Answer

Correct option: B.

$\lambda=\pi y_0 / 2$

Particle velocity $\begin{aligned} v & =\frac{d y}{d t}=2 \pi y_0 \cos \{2 \pi(f t-x / \lambda)\} \\ v_{\max } & =2 \pi f y_0 \quad \text {} \\ v_{\max } & =2 \pi f y_0=4 f \lambda \\ \Rightarrow \quad \lambda & =\frac{\pi y_0}{2}\end{aligned}$

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MCQ 711 Mark

The velocity of sound in are is not affected by change in the …….

✓
atmospheric pressure
B
moisture content of air
C
temperature of air
D
composition of air

Answer

Correct option: A.

atmospheric pressure

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MCQ 721 Mark

Speed of sound in a gas in proportional to …….

A
square root of isothermal elasticity
✓
square root of adiabatic elasticity
C
isothermal elasticity
D
adiabatic elasticity

Answer

Correct option: B.

square root of adiabatic elasticity

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MCQ 731 Mark

With the rise of temperature, the speed of sound in a gas ……..

✓
increases
B
decreases
C
remain the same
D
may increase or decrease depending on the corresponding change in pressure.

Answer

Correct option: A.

increases

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MCQ 741 Mark

A transverse wave of amplitude 0.5m, wavelength 1 m and frequency 2Hz is propogating in a string in the negative x direction. The equation of this wave is ….

A
y = 0.5 sin (2πx – 4πt)
✓
y = 0.5 sin (2πx + 4πt)
C
y = 0.5 sin (πx – 2πt)
D
y = 0.5 cos (kx – 2πt)

Answer

Correct option: B.

y = 0.5 sin (2πx + 4πt)

y = 0.5 sin (2πx + 4πt)
Hint:
y = A sin(kx + ωt)
Here A = 0.5 m

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MCQ 751 Mark

Ultrasonic waves are those waves which ………

✓
human beings cannot hear
B
human beings can hear
C
have high velocity
D
have large amplitude

Answer

Correct option: A.

human beings cannot hear

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MCQ 761 Mark

The diagram shows the profile of a wave, which of the following pairs of points are in phase?

A
A, B
B
B, C
C
B, D
✓
B, E

Answer

Correct option: D.

B, E

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MCQ 771 Mark

The equation of a wave is $y=4 \sin \left\{\frac{\pi}{2}\left(2 t+\frac{x}{8}\right)\right\}$ where $y, x$ are in $cm$ and $t$ in seconds. The amplitude wavelength, velocity and frequency of the wave are, respectively, .......

✓
4 cm, 32 cm, 16 cm/s, 0.5 Hz
B
8 cm, 16 cm, 32 cm/s, 1.0 Hz
C
4 cm, 32 cm, 32 cm/s, 0.5 Hz
D
8 cm, 16 cm, 16 cm/s, 1.0 Hz

Answer

Correct option: A.

4 cm, 32 cm, 16 cm/s, 0.5 Hz

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MCQ 781 Mark

The equation of a wave travelling on a string is $y=4 \sin \left\{\frac{\pi}{2}\left(8 t-\frac{x}{8}\right)\right\}$, where $x , y$ are in $cm$ and $t$ in seconds. The velocity of the waves is .......

A
64 cm/s in – x direction
B
32 cm/s in – x direction
C
32 cm/s in +x direction
✓
64 cm/s in + x direction

Answer

Correct option: D.

64 cm/s in + x direction

64 cm/s in + x direction to S
Hint :
Velocity $v=\frac{\omega}{k}=\frac{8}{1 / 8}=64 cm / s$ in $+x$ direction.

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MCQ 791 Mark

A wave of frequency $500$ Hzhas a velocity $300 m/s$. The distance between two nearest points which are $60°$ out of phase, is ……

A
$0.2 m$
✓
$0.1 m$
C
$0.4 m$
D
$0.5 m$

Answer

Correct option: B.

$0.1 m$

$0.1 cm$
{ Hint: }
$ \lambda=\frac{300}{500}=0.6 m $
$ \Delta x=\frac{\lambda}{2 \pi} \cdot \Delta \phi=\frac{0.6}{2 \pi} \cdot \frac{\pi}{3}=0.1 m $

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MCQ 801 Mark

The equation of a wave travelling in a string can be written as y = 3 cos {π(100t – x)} where y and x are in cm and t is in seconds. Then the value of wavelength is …….

A
100 cm
✓
2 cm
C
50 cm
D
4 cm

Answer

Correct option: B.

2 cm

2 cm
Hint :
On comparing given equation with $y = A \cos ( kx -\omega t )$, we get
$
\lambda=\frac{2 \pi}{k}=\frac{2 \pi}{\pi}=2 cm \quad[\therefore k=\pi]
$

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MCQ 811 Mark

The speed of the wave represented by y = A sin(ωt – kx) is ……..

A
$k / w$
✓
$\omega / k$
C
$\omega k$
D
$1 / w k$

Answer

Correct option: B.

$\omega / k$

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MCQ 821 Mark

Transverse waves can propagate ……

A
both in a gas and in a metal
B
in a gas but not in a metal
✓
not in a gas but in a metal
D
neither in a gas nor in a metal

Answer

Correct option: C.

not in a gas but in a metal

not in a gas but in a metal.

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MCQ 831 Mark

Choose the correct statement:

A
sound waves are transverse waves
B
sound travels fastest through vaccum.
✓
sound travels faster in solids than in gases.
D
sound travels faster in gases than in liquids.

Answer

Correct option: C.

sound travels faster in solids than in gases.

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MCQ 841 Mark

A boat at anchor is rocked by waves of velocity 25m/s, having crests 100 m apart. The boat bounches up once in every

✓
4.0s
B
2500s
C
0.25s
D
75s

Answer

Correct option: A.

4.0s

4.0s
Hint :
$\lambda$ = distance between crests $=100 m$ frequency $v =\frac{25}{100}=\frac{1}{4} s ^{-1}$ Therefore, the crests reach the boat once every 4 seconds.

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MCQ 851 Mark

Sound travels fastest in …….

✓
Steel
B
air
C
water
D
vaccum

Answer

Correct option: A.

Steel

steel

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MCQ 861 Mark

Sound whose frequency is 50 Hz?

✓
has a relatively short wavelength.
B
has a relatively long wavelength
C
is very loud
D
is very intense

Answer

Correct option: A.

has a relatively short wavelength.

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MCQ 871 Mark

Mechanical Waves

A
are longitudinal only
B
are transverse only
✓
can be both longitudinal and transverse.
D
are neither longitudinal for transverse waves.

Answer

Correct option: C.

can be both longitudinal and transverse.

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Physics MCQ