Sound

Chapter 18 MCQs

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

1

A sound wave travels through air from left to right.

Which statement describes the motion of the air particles?

A particles move permanently from left to right
B particles vibrate left and right, parallel to the direction of wave travel
C particles vibrate up and down, perpendicular to wave travel
D particles remain completely stationary

2

Which statement explains why sound cannot travel through a vacuum?

A sound is an electromagnetic wave
B sound needs particles to vibrate and transfer energy
C sound travels too fast in a vacuum to be heard
D sound has no frequency in a vacuum

3

In which material does sound usually travel fastest?

A air
B water
C steel
D vacuum

4

A student claps near a large wall and hears the echo 0.80 s later.

Speed of sound in air = 340 m/s.

How far is the student from the wall?

A 136 m
B 170 m
C 272 m
D 425 m

5

A ship sends an ultrasound pulse vertically downwards. The echo from the seabed is received after 1.60 s.

Speed of ultrasound in seawater = 1500 m/s.

What is the depth of the sea?

A 469 m
B 750 m
C 1200 m
D 2400 m

6

An ultrasound pulse is sent towards a wall 45 m away. The echo returns after 0.060 s.

What is the speed of ultrasound in the material?

A 750 m/s
B 1500 m/s
C 3000 m/s
D 5400 m/s

7

A sound wave has frequency 680 Hz and speed 340 m/s.

What is its wavelength?

A 0.25 m
B 0.50 m
C 2.0 m
D 231 200 m

8

A sound wave has wavelength 0.85 m in air. Speed of sound in air = 340 m/s.

What is the frequency?

A 0.0025 Hz
B 289 Hz
C 400 Hz
D 578 Hz

9

A tuning fork produces sound of frequency 256 Hz.

What is the period of vibration?

A 0.00391 s
B 0.256 s
C 3.91 s
D 256 s

10

A sound wave has period 0.0025 s and wavelength 0.85 m.

What is the speed of the sound wave?

A 0.0021 m/s
B 2.9 m/s
C 340 m/s
D 425 m/s

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11

A sound wave travels from air into water. Its frequency is 500 Hz in air.

What is the frequency in water?

A less than 500 Hz
B 500 Hz
C greater than 500 Hz
D zero

12

A sound wave travels from air into water. The speed increases from 340 m/s to 1500 m/s. The frequency remains 500 Hz.

What happens to the wavelength?

A decreases from 0.68 m to 0.23 m
B increases from 0.68 m to 3.0 m
C remains 0.68 m
D increases from 500 m to 1500 m

13

A sound wave has a higher pitch than another sound wave.

Which quantity is greater?

A amplitude
B frequency
C wavelength only
D speed in air only

14

A sound is made louder but its pitch is unchanged.

Which change has occurred?

A amplitude has increased, frequency unchanged
B frequency has increased, amplitude unchanged
C wavelength has increased, frequency unchanged
D speed has increased, amplitude unchanged

15

Two sound waves travel through the same air.

Wave X has frequency 200 Hz and amplitude 1.0 mm.
Wave Y has frequency 400 Hz and amplitude 0.50 mm.

Which statement is correct?

A X is louder and higher pitched than Y
B X is quieter and lower pitched than Y
C Y is louder and higher pitched than X
D X is louder and lower pitched than Y

16

A sound is displayed on a cathode-ray oscilloscope. The trace has a larger vertical height but the same horizontal spacing between peaks.

Which statement is correct?

A sound is louder, pitch unchanged
B sound is quieter, pitch higher
C sound is louder, pitch higher
D sound is quieter, pitch unchanged

17

A CRO trace shows 5 complete waves across a screen width of 10 ms.

What is the frequency of the sound?

A 50 Hz
B 200 Hz
C 500 Hz
D 2000 Hz

18

On an oscilloscope, one complete wave occupies 4.0 divisions. The time-base is 0.50 ms/division.

What is the frequency of the sound?

A 125 Hz
B 250 Hz
C 500 Hz
D 2000 Hz

19

An oscilloscope trace has peak-to-peak height 6.0 cm. The vertical scale is 0.20 V/cm.

What is the amplitude of the signal voltage?

A 0.60 V
B 1.2 V
C 3.0 V
D 6.0 V

20

A microphone connected to an oscilloscope detects a sound. The trace becomes closer together horizontally, but the vertical height is unchanged.

What happens to the sound?

A pitch increases, loudness unchanged
B pitch decreases, loudness unchanged
C loudness increases, pitch unchanged
D loudness decreases, pitch unchanged

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

21

Which frequency is ultrasound?

A 10 Hz
B 100 Hz
C 10 000 Hz
D 40 000 Hz

22

The approximate range of frequencies audible to a healthy young human is:

A 2 Hz to 200 Hz
B 20 Hz to 20 000 Hz
C 200 Hz to 200 000 Hz
D 20 000 Hz to 2 000 000 Hz

23

Which frequency is most likely to be described as infrasound?

A 5 Hz
B 500 Hz
C 5000 Hz
D 50 000 Hz

24

A sound has frequency 25 kHz.

Which statement is correct?

A it is below the human audible range
B it is within the human audible range
C it is ultrasound
D it must be electromagnetic radiation

25

Ultrasound is used in medical scanning mainly because it:

A is ionising and damages tissue strongly
B can reflect at boundaries between tissues
C cannot travel through liquids
D travels only in a vacuum

26

Ultrasound is sent into a patient’s body. A boundary between two tissues is 3.0 cm below the skin. The speed of ultrasound in tissue is 1500 m/s.

What is the time between sending the pulse and receiving the echo?

A 2.0 × 10⁻⁵ s
B 4.0 × 10⁻⁵ s
C 2.0 × 10⁻⁴ s
D 4.0 × 10⁻⁴ s

27

In ultrasound imaging, gel is placed between the probe and the skin.

Why?

A to cool the ultrasound until it becomes audible
B to remove air gaps that would strongly reflect ultrasound
C to reduce the frequency to below 20 Hz
D to turn ultrasound into X-rays

28

A sonar system sends out a pulse every 0.50 s. Speed of sound in water = 1500 m/s.

What is the greatest depth that can be measured without receiving the echo after the next pulse is sent?

A 188 m
B 375 m
C 750 m
D 1500 m

29

A bat emits ultrasound of frequency 60 kHz. The wavelength in air is approximately 5.7 mm.

What speed of sound does this imply?

A 0.34 m/s
B 34 m/s
C 342 m/s
D 3420 m/s

30

A dolphin emits ultrasound of wavelength 3.0 cm in water. Speed of sound in water = 1500 m/s.

What is the frequency?

A 50 Hz
B 500 Hz
C 50 000 Hz
D 500 000 Hz

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

31

A sound wave moves through air. At a compression:

A particles are farther apart than normal and pressure is low
B particles are closer together than normal and pressure is high
C particles are stationary and pressure is zero
D particles move perpendicular to the wave direction

32

A rarefaction in a sound wave is a region where:

A particles are closer together and pressure is higher
B particles are farther apart and pressure is lower
C particles stop vibrating
D sound speed becomes zero

33

The distance between the centre of one compression and the centre of the next compression is:

A amplitude
B wavelength
C period
D frequency

34

A sound wave has wavelength 0.40 m. What is the distance from the centre of a compression to the centre of the next rarefaction?

A 0.10 m
B 0.20 m
C 0.40 m
D 0.80 m

35

A loudspeaker cone moves forwards and backwards 500 times per second.

Which sound does it produce in air?

A frequency 500 Hz
B wavelength 500 m
C speed 500 m/s
D period 500 s

36

A student strikes a tuning fork and then touches it lightly.

The sound becomes quieter mainly because:

A the frequency decreases
B the amplitude of vibration decreases
C the speed of sound decreases
D the wavelength becomes zero

37

A guitar string is tightened. It then produces a note of higher pitch.

Which wave quantity in the sound has increased?

A amplitude
B frequency
C speed in air
D period

38

A sound wave has speed 330 m/s and frequency 110 Hz. The frequency is increased to 220 Hz in the same air.

What is the new wavelength?

A 0.75 m
B 1.5 m
C 3.0 m
D 6.0 m

39

Two notes are played in the same room.

Note P has frequency 440 Hz.
Note Q has frequency 880 Hz.

Which statement is correct?

A Q has twice the pitch and half the wavelength of P
B Q has twice the pitch and twice the wavelength of P
C Q has half the pitch and twice the wavelength of P
D both notes have different speeds in the same air

40

A sound wave in air has wavelength 1.7 m. Speed of sound = 340 m/s.

Which statement is correct?

A frequency is 200 Hz and period is 0.0050 s
B frequency is 200 Hz and period is 200 s
C frequency is 578 Hz and period is 0.0050 s
D frequency is 0.0050 Hz and period is 200 s

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41

An echo is heard only if the reflected sound arrives at least 0.10 s after the original sound.

Speed of sound in air = 340 m/s.

What is the minimum distance to a flat wall for a distinct echo?

A 17 m
B 34 m
C 68 m
D 340 m

42

A person shouts between two parallel cliffs. The first echo is heard after 0.60 s and the second echo after 1.40 s.

Speed of sound = 340 m/s.

What is the distance between the cliffs?

A 136 m
B 238 m
C 340 m
D 680 m

43

A student estimates the speed of sound by standing 170 m from a wall and clapping. The echo is heard 1.0 s after the clap.

What speed is calculated?

A 85 m/s
B 170 m/s
C 340 m/s
D 510 m/s

44

A starter pistol is fired 850 m away from a student. The student sees the flash immediately and hears the sound 2.5 s later.

What speed of sound is calculated?

A 212 m/s
B 340 m/s
C 850 m/s
D 2125 m/s

45

Why is a distant lightning flash seen before thunder is heard?

A light travels faster than sound in air
B sound travels faster than light in air
C thunder is produced after the lightning flash
D light needs air but sound does not

46

A soundproof room has soft foam on the walls.

The foam mainly reduces echoes because it:

A absorbs sound energy
B increases the speed of sound
C reflects all sound perfectly
D changes sound into ultraviolet radiation

47

A hard flat wall produces a clearer echo than a curtain because the wall:

A absorbs more sound than the curtain
B reflects more sound than the curtain
C makes sound travel faster
D changes longitudinal waves into transverse waves

48

A sound wave and a light wave both travel through air.

Which statement is correct?

A both are longitudinal
B both require a material medium
C sound is longitudinal and light is transverse
D sound travels faster than light

49

A sound wave travels from cold air into warmer air. The speed of sound is greater in warmer air. The frequency remains unchanged.

What happens to the wavelength?

A decreases
B remains unchanged
C increases
D becomes zero

50

A student says, “A louder sound must travel faster through air than a quieter sound.”

Which correction is best?

A loudness changes amplitude, not the speed of sound in the same medium
B louder sounds have lower frequency, so speed decreases
C quieter sounds cannot travel through air
D sound speed depends only on amplitude

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

Chapter 18 Answer Key

Q	Ans	Q	Ans	Q	Ans	Q	Ans	Q	Ans
1	B	11	B	21	D	31	B	41	A
2	B	12	B	22	B	32	B	42	C
3	C	13	B	23	A	33	B	43	C
4	A	14	A	24	C	34	B	44	B
5	C	15	D	25	B	35	A	45	A
6	B	16	A	26	B	36	B	46	A
7	B	17	C	27	B	37	B	47	B
8	C	18	C	28	B	38	B	48	C
9	A	19	A	29	C	39	A	49	C
10	C	20	A	30	C	40	A	50	A

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

Detailed Explanations

1. B

Sound in air is a longitudinal wave.
The air particles vibrate backwards and forwards.
Their vibration is parallel to the direction of wave travel.
They do not move permanently with the wave.

2. B

Sound needs particles to vibrate.
A vacuum has no particles.
So sound cannot travel through a vacuum.
Light can travel through a vacuum because it is electromagnetic; sound cannot.

3. C

Sound usually travels fastest in solids.
Steel is a solid, so sound travels fastest in steel.
Sound travels slower in liquids and slowest in gases.
Sound cannot travel in a vacuum.

4. A

Echo time = time for sound to travel to the wall and back.
Total distance travelled by sound:
- distance = speed × time
- distance = 340 × 0.80 = 272 m
Distance to wall:
- 272 / 2 = 136 m

5. C

Ultrasound travels down to the seabed and back up.
Total distance = speed × time
Total distance = 1500 × 1.60 = 2400 m
Depth = 2400 / 2 = 1200 m

6. B

The pulse travels to the wall and back.
Total distance = 45 × 2 = 90 m
Speed = distance / time
Speed = 90 / 0.060
Speed = 1500 m/s

7. B

v = fλ
λ = v / f
λ = 340 / 680
λ = 0.50 m

8. C

v = fλ
f = v / λ
f = 340 / 0.85
f = 400 Hz

9. A

Period = 1 / frequency
T = 1 / 256
T = 0.00391 s

10. C

Period = 0.0025 s
Frequency = 1 / 0.0025 = 400 Hz
v = fλ
v = 400 × 0.85
v = 340 m/s

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

11. B

Frequency is determined by the source.
When sound passes from air into water, frequency remains unchanged.
So the frequency in water is still 500 Hz.

12. B

In air:
- λ = v / f
- λ = 340 / 500 = 0.68 m
In water:
- λ = 1500 / 500 = 3.0 m
Wavelength increases from 0.68 m to 3.0 m.

13. B

Pitch depends on frequency.
Higher pitch means higher frequency.
Amplitude affects loudness, not pitch.

14. A

Loudness depends on amplitude.
Pitch depends on frequency.
If sound becomes louder but pitch is unchanged:
- amplitude increases
- frequency stays unchanged

15. D

Wave X:
- frequency = 200 Hz
- amplitude = 1.0 mm
Wave Y:
- frequency = 400 Hz
- amplitude = 0.50 mm
X has greater amplitude, so it is louder.
X has lower frequency, so it is lower pitched.
Answer = X is louder and lower pitched than Y.

16. A

Larger vertical height on a CRO trace means greater amplitude.
Greater amplitude means louder sound.
Same horizontal spacing means same period and same frequency.
Pitch is unchanged.

17. C

5 complete waves take 10 ms.
10 ms = 0.010 s
Frequency = number of waves / time
f = 5 / 0.010
f = 500 Hz

18. C

One wave occupies 4.0 divisions.
Time-base = 0.50 ms/division.
Period = 4.0 × 0.50 = 2.0 ms = 0.0020 s
Frequency = 1 / 0.0020
Frequency = 500 Hz

19. A

Peak-to-peak height = 6.0 cm.
Amplitude is half of peak-to-peak height.
Amplitude height = 3.0 cm.
Vertical scale = 0.20 V/cm.
Voltage amplitude = 3.0 × 0.20
Voltage amplitude = 0.60 V

20. A

Trace becomes closer together horizontally.
This means period decreases.
Frequency increases, so pitch increases.
Vertical height unchanged means amplitude unchanged, so loudness unchanged.

21. D

Ultrasound has frequency above 20 000 Hz.
40 000 Hz is above the human audible range.
Therefore it is ultrasound.

22. B

Approximate audible range for a healthy young human:
- 20 Hz to 20 000 Hz
Below 20 Hz is infrasound.
Above 20 000 Hz is ultrasound.

23. A

Infrasound is below 20 Hz.
5 Hz is below 20 Hz.
So 5 Hz is infrasound.

24. C

25 kHz = 25 000 Hz.
This is above 20 000 Hz.
Therefore it is ultrasound.
It is still sound, not electromagnetic radiation.

25. B

Ultrasound reflects at boundaries between different tissues.
These echoes are detected and used to form images.
Ultrasound is not ionising, unlike X-rays or gamma rays.

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

26. B

Depth = 3.0 cm = 0.030 m.
Echo travels down and back.
Total distance = 2 × 0.030 = 0.060 m
Time = distance / speed
Time = 0.060 / 1500
Time = 4.0 × 10⁻⁵ s

27. B

Air gaps strongly reflect ultrasound.
Gel removes air gaps between the probe and skin.
This allows ultrasound to enter the body more effectively.
No, it does not magically turn ultrasound into X-rays. Physics is not doing side quests.

28. B

Echo must return before the next pulse is sent.
Maximum echo time = 0.50 s.
Total distance travelled by sound:
- distance = 1500 × 0.50 = 750 m
Greatest depth:
- 750 / 2 = 375 m

29. C

Frequency = 60 kHz = 60 000 Hz.
Wavelength = 5.7 mm = 0.0057 m.
Speed = fλ
Speed = 60 000 × 0.0057
Speed = 342 m/s

30. C

Wavelength = 3.0 cm = 0.030 m.
Speed = 1500 m/s.
f = v / λ
f = 1500 / 0.030
f = 50 000 Hz

31. B

A compression is a region where particles are closer together than normal.
Pressure is higher in a compression.
Rarefaction is the opposite.

32. B

A rarefaction is a region where particles are farther apart than normal.
Pressure is lower in a rarefaction.
Sound speed does not become zero in a rarefaction.

33. B

Wavelength in a longitudinal wave can be measured from:
- compression to next compression
- rarefaction to next rarefaction
Therefore the answer is wavelength.

34. B

Compression to next compression = 1 wavelength.
Compression to next rarefaction = half a wavelength.
λ = 0.40 m.
Distance = 0.40 / 2 = 0.20 m

35. A

The loudspeaker cone vibrates 500 times per second.
Frequency = vibrations per second.
So the sound has frequency 500 Hz.

36. B

Touching the tuning fork reduces the amplitude of vibration.
Smaller amplitude means quieter sound.
Frequency does not mainly change.

37. B

Higher pitch means higher frequency.
Tightening a guitar string makes it vibrate at a higher frequency.
Speed of sound in the same air is unchanged.

38. B

Speed in same air = 330 m/s.
New frequency = 220 Hz.
λ = v / f
λ = 330 / 220
λ = 1.5 m

39. A

Q has frequency 880 Hz.
P has frequency 440 Hz.
Q has twice the frequency, so it has higher pitch.
In the same air, speed is the same.
Since v = fλ, doubling frequency halves wavelength.
Q has twice the pitch and half the wavelength of P.

40. A

v = fλ
f = 340 / 1.7
f = 200 Hz
Period = 1 / f
T = 1 / 200
T = 0.0050 s

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

41. A

For a distinct echo, reflected sound must arrive at least 0.10 s later.
Total distance travelled by sound:
- distance = 340 × 0.10 = 34 m
Distance to wall:
- 34 / 2 = 17 m

42. C

First echo:
- distance to first cliff = speed × time / 2
- distance = 340 × 0.60 / 2 = 102 m
Second echo:
- distance to second cliff = 340 × 1.40 / 2 = 238 m
Distance between cliffs:
- 102 + 238 = 340 m

43. C

Echo travels to the wall and back.
Total distance = 2 × 170 = 340 m
Speed = distance / time
Speed = 340 / 1.0
Speed = 340 m/s

44. B

The flash is seen almost immediately because light is much faster.
Sound takes 2.5 s to travel 850 m.
Speed = distance / time
Speed = 850 / 2.5
Speed = 340 m/s

45. A

Light travels much faster than sound in air.
So the lightning flash is seen before thunder is heard.
Thunder is produced essentially at the same event, but sound arrives later.

46. A

Soft foam absorbs sound energy.
This reduces reflection.
Less reflection means fewer/weaker echoes.

47. B

A hard flat wall reflects sound well.
A curtain absorbs more sound.
Therefore the wall produces a clearer echo.

48. C

Sound in air is longitudinal.
Light is transverse.
Sound needs a medium.
Light can travel through a vacuum.

49. C

Speed of sound is greater in warmer air.
Frequency remains unchanged.
v = fλ
If speed increases and frequency stays the same, wavelength increases.

50. A

Loudness depends on amplitude.
Speed of sound in the same medium does not depend on loudness.
A louder sound has greater amplitude, not greater speed.
Classic misconception: louder does not mean faster.

For Full Scale Course: Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total Personal A Grades, 11 World Records and 7 Distinctions, Educate A Change.

Common Traps From This Chapter

Trap	Correct Rule
Sound in air	longitudinal wave
Particle motion in sound	parallel to wave direction
Sound in vacuum	impossible; needs particles
Fastest sound usually	solids > liquids > gases
Echo distance	sound travels there and back
Depth by sonar	divide total distance by 2
Wave equation	v = fλ
Period	T = 1/f
Pitch	frequency
Loudness	amplitude
CRO vertical height	amplitude/loudness
CRO horizontal spacing	period/frequency
Peak-to-peak height	2 × amplitude
Human hearing	about 20 Hz to 20 000 Hz
Ultrasound	above 20 000 Hz
Infrasound	below 20 Hz
Ultrasound imaging	echoes at tissue boundaries
Ultrasound gel	removes air gaps
Compression	high pressure, particles close
Rarefaction	low pressure, particles spread out
Compression to next compression	one wavelength
Compression to next rarefaction	half wavelength
Same air, higher frequency	shorter wavelength
Distinct echo minimum distance	use round trip
Foam/curtain	absorbs sound
Hard wall	reflects sound
Louder sound	does not travel faster

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