Chapter 15 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 source produces 75 complete waves in 30 s.

What is the frequency of the waves?

A 0.40 Hz
B 2.5 Hz
C 45 Hz
D 2250 Hz

---

2

A wave has frequency 8.0 Hz.

What is its period?

A 0.080 s
B 0.125 s
C 8.0 s
D 64 s

---

3

A wave has wavelength 0.60 m and frequency 25 Hz.

What is the wave speed?

A 0.024 m/s
B 15 m/s
C 25.6 m/s
D 41.7 m/s

---

4

A water wave travels 12 m in 4.0 s. The distance between adjacent crests is 0.75 m.

What is the frequency of the wave?

A 0.063 Hz
B 0.25 Hz
C 4.0 Hz
D 16 Hz

---

5

A wave has speed 340 m/s and period 0.0020 s.

What is its wavelength?

A 0.0000059 m
B 0.68 m
C 170 000 m
D 680 000 m

---

6

A student measures the time for 20 waves to pass a point as 5.0 s. The wavelength is 0.40 m.

What is the wave speed?

A 0.080 m/s
B 1.6 m/s
C 4.0 m/s
D 25 m/s

---

7

A wave moves along a rope. The particles of the rope move up and down while the wave travels horizontally.

What type of wave is this?

A longitudinal
B transverse
C electromagnetic only
D stationary only

---

8

In a longitudinal wave, the direction of particle vibration is:

A perpendicular to the direction of energy transfer
B parallel to the direction of energy transfer
C always vertically upwards
D always in a circular path

---

9

Which row correctly identifies the waves?

	transverse	longitudinal
A	sound in air	light
B	water surface waves only	electromagnetic waves
C	electromagnetic waves	sound in air
D	compression waves	ripples only

---

10

A wave transfers energy from left to right. The particles of the medium vibrate from left to right.

Which statement is correct?

A The wave is transverse.
B The wave is longitudinal.
C The wave must be electromagnetic.
D The wave transfers matter from left to right.

---

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

Which statement about waves is correct?

A Waves transfer matter without energy.
B Waves transfer energy without overall transfer of matter.
C Waves always need a material medium.
D Waves can only travel in straight lines.

---

12

The amplitude of a transverse wave is:

A the distance between two adjacent crests
B the maximum displacement from the rest position
C the number of waves passing a point per second
D the time for one complete wave to pass

---

13

The wavelength of a transverse wave is the distance from:

A crest to trough
B midpoint to crest
C crest to the next crest
D rest position to maximum displacement

---

14

A transverse wave has amplitude 3.0 cm. The vertical distance from crest to trough is:

A 1.5 cm
B 3.0 cm
C 6.0 cm
D 9.0 cm

---

15

A student measures the horizontal distance from one crest to the fifth crest as 2.4 m.

What is the wavelength?

A 0.48 m
B 0.60 m
C 2.4 m
D 12 m

---

16

A student measures the distance from one compression to the sixth compression in a longitudinal wave as 1.50 m.

What is the wavelength?

A 0.25 m
B 0.30 m
C 1.50 m
D 9.0 m

---

17

A wave has frequency 12 Hz. The distance from the first crest to the fourth crest is 0.90 m.

What is the wave speed?

A 3.6 m/s
B 4.8 m/s
C 10.8 m/s
D 36 m/s

---

18

A wave has period 0.040 s and wavelength 1.5 m.

How far does the wave travel in 2.0 s?

A 0.030 m
B 37.5 m
C 75 m
D 300 m

---

19

A ripple tank produces waves with frequency 20 Hz. The distance between 11 consecutive wavefronts is 5.0 cm.

What is the wave speed?

A 0.010 m/s
B 0.10 m/s
C 1.0 m/s
D 10 m/s

---

20

A wavefront diagram shows straight wavefronts 4.0 cm apart. The wavefronts pass a point every 0.20 s.

What is the wave speed?

A 0.020 m/s
B 0.20 m/s
C 5.0 m/s
D 20 m/s

---

21

A ray on a wavefront diagram shows:

A the direction of vibration of particles only
B the direction of energy transfer
C the distance between wavefronts
D the amplitude of the wave

---

22

Wavefronts are drawn close together in one region and farther apart in another region.

What does this show?

A amplitude is greater where wavefronts are close together
B wavelength is smaller where wavefronts are close together
C frequency is zero where wavefronts are close together
D the wave cannot travel there

---

23

A water wave travels from deep water into shallow water. Its frequency is 12 Hz in deep water.

What is its frequency in shallow water?

A less than 12 Hz
B 12 Hz
C greater than 12 Hz
D zero

---

24

A water wave travels from deep water into shallow water.

Which row is correct?

	speed	wavelength	frequency
A	decreases	decreases	unchanged
B	decreases	unchanged	decreases
C	unchanged	decreases	increases
D	increases	increases	unchanged

---

25

A straight water wave travels from deep water into shallow water at an angle to the boundary.

What happens to its direction?

A it bends towards the normal
B it bends away from the normal
C it continues without any change of direction
D it reflects back completely every time

---

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

A water wave travels from shallow water into deep water at an angle to the boundary.

What happens to its speed and direction?

	speed	direction
A	decreases	towards the normal
B	decreases	away from the normal
C	increases	towards the normal
D	increases	away from the normal

---

27

Water waves pass from deep water to shallow water. The speed changes from 0.40 m/s to 0.25 m/s. The wavelength in deep water is 0.080 m.

What is the wavelength in shallow water?

A 0.020 m
B 0.050 m
C 0.080 m
D 0.128 m

---

28

Water waves move from region X to region Y. In X, the wavelength is 6.0 cm and the speed is 0.30 m/s. In Y, the wavelength is 4.0 cm.

What is the speed in Y?

A 0.20 m/s
B 0.30 m/s
C 0.45 m/s
D 1.8 m/s

---

29

A wave crosses a boundary between two media. Its speed decreases but its frequency stays the same.

Which statement must be correct?

A wavelength decreases
B wavelength increases
C amplitude becomes zero
D period increases

---

30

A wave travels into a new medium. Its wavelength increases while its frequency stays unchanged.

What happens to its speed?

A decreases
B stays unchanged
C increases
D becomes zero

---

31

A ripple tank shows plane waves striking a straight barrier at an angle of incidence of 35°.

What is the angle of reflection?

A 17.5°
B 35°
C 55°
D 70°

---

32

Plane water waves reflect from a straight barrier.

Which quantity changes during reflection?

A frequency
B speed in the same water
C wavelength in the same water
D direction of travel

---

33

A wave reflects from a barrier. The reflected wave remains in the same medium.

Which row is correct?

	frequency	wavelength	speed
A	unchanged	unchanged	unchanged
B	unchanged	decreases	decreases
C	decreases	unchanged	decreases
D	increases	increases	unchanged

---

34

A straight wavefront is incident on a straight barrier. The angle between the wavefront and the barrier is 25°.

What is the angle of incidence?

A 25°
B 50°
C 65°
D 75°

---

35

A ray is incident on a straight barrier at 60° to the barrier.

What is the angle between the reflected ray and the normal?

A 30°
B 60°
C 90°
D 120°

---

36

Water waves pass through a narrow gap and spread out.

This effect is called:

A reflection
B refraction
C diffraction
D dispersion

---

37

Diffraction is greatest when the gap size is:

A much smaller than the wavelength
B similar to the wavelength
C much larger than the wavelength
D exactly zero

---

38

Two gaps are used in a ripple tank.

• Gap X has width 2.0 cm.

• Gap Y has width 12 cm.

• The water wave wavelength is 2.5 cm.

Which statement is correct?

A Gap X gives more diffraction than gap Y.
B Gap Y gives more diffraction than gap X.
C Both gaps give no diffraction.
D Diffraction depends only on wave speed, not gap size.

---

39

Plane waves pass through a narrow gap into the same depth of water.

Which quantities remain unchanged after passing through the gap?

A speed and frequency
B speed only
C frequency only
D wavelength and amplitude only

---

40

A wave passes through a narrow gap into water of the same depth. The wave spreads out.

Which statement is correct?

A The spreading shows diffraction.
B The frequency increases because of the gap.
C The speed decreases because of the gap.
D The wavelength must become zero.

---

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 ripple tank is used to observe water waves. The lamp and screen make the waves easier to see because:

A crests and troughs focus light differently
B water becomes radioactive
C wave speed becomes zero
D the screen produces the waves

---

42

In a ripple tank, the frequency of the dipper is increased while the water depth stays the same.

What happens to the wavelength?

A decreases
B stays the same
C increases
D becomes infinite

---

43

In a ripple tank, the water depth is unchanged. The wave frequency is changed from 5.0 Hz to 8.0 Hz. The original wavelength is 4.8 cm.

What is the new wavelength?

A 3.0 cm
B 4.8 cm
C 7.7 cm
D 12.8 cm

---

44

A wave has amplitude 2.0 cm and wavelength 8.0 cm. Its frequency is doubled while the wave speed stays constant.

What are the new amplitude and wavelength?

	amplitude	wavelength
A	unchanged	halves
B	unchanged	doubles
C	doubles	halves
D	halves	unchanged

---

45

A source produces waves in a medium. The source frequency is doubled, and the wave speed in the medium is unchanged.

Which statement is correct?

A period doubles and wavelength doubles
B period halves and wavelength halves
C period halves and wavelength doubles
D period doubles and wavelength halves

---

46

A wave has frequency f, wavelength λ and speed v.

Which row shows the changes if the frequency is halved but speed is unchanged?

	period	wavelength
A	doubles	doubles
B	doubles	halves
C	halves	doubles
D	halves	halves

---

47

A water wave has speed 0.60 m/s and period 0.15 s.

What is its wavelength?

A 0.090 m
B 0.45 m
C 4.0 m
D 9.0 m

---

48

A vibrating source produces waves of wavelength 0.080 m at a frequency of 25 Hz. The source frequency is then increased to 40 Hz. The wave speed is unchanged.

What is the new wavelength?

A 0.050 m
B 0.080 m
C 0.128 m
D 2.0 m

---

49

A wave travels from left to right. Points P and Q on the wave are separated by one wavelength.

Which statement is correct?

A P and Q vibrate exactly in phase.
B P and Q always have opposite displacements.
C P and Q are always at rest.
D P has twice the frequency of Q.

---

50

A transverse wave travels along a rope. Point X is at a crest and point Y is at the next trough.

What is the phase difference between X and Y?

A 0°
B 90°
C 180°
D 360°

---

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 15 Answer Key

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

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

• Frequency = number of waves / time

• f = 75 / 30

• f = 2.5 Hz

2. B

• Period = 1 / frequency

• T = 1 / 8.0

• T = 0.125 s

3. B

• Wave speed = frequency × wavelength

• v = fλ

• v = 25 × 0.60

• v = 15 m/s

4. C

• Wave speed = distance / time

• v = 12 / 4.0 = 3.0 m/s

• v = fλ

• f = v / λ

• f = 3.0 / 0.75

• f = 4.0 Hz

5. B

• Period is given.

• Wave speed = wavelength / period

• So wavelength = speed × period

• λ = 340 × 0.0020

• λ = 0.68 m

6. B

• Frequency = 20 / 5.0

• f = 4.0 Hz

• v = fλ

• v = 4.0 × 0.40

• v = 1.6 m/s

7. B

• Rope particles move up and down.

• Wave energy travels horizontally.

• Vibration is perpendicular to wave travel.

• This is a transverse wave.

8. B

• In a longitudinal wave, particles vibrate parallel to the direction of energy transfer.

• Sound in air is the classic example.

9. C

• Electromagnetic waves are transverse.

• Sound waves in air are longitudinal.

• So the correct row is C.

10. B

• Particles vibrate from left to right.

• Energy also transfers from left to right.

• Vibration is parallel to energy transfer.

• Therefore the wave is longitudinal.

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

• Waves transfer energy from one place to another.

• There is no overall transfer of matter.

• Individual particles may vibrate, but they do not travel along with the wave overall.

12. B

• Amplitude = maximum displacement from the rest position.

• It is not crest-to-crest distance.

• Crest-to-crest distance is wavelength.

13. C

• Wavelength is the distance between two adjacent points in phase.

• For a transverse wave, this may be:

  • crest to next crest

  • trough to next trough

14. C

• Amplitude = distance from rest position to crest.

• Crest-to-trough distance = 2 × amplitude.

• Distance = 2 × 3.0

• Distance = 6.0 cm

15. B

• From the first crest to the fifth crest, there are 4 wavelengths.

• 4λ = 2.4 m

• λ = 2.4 / 4

• λ = 0.60 m

16. B

• From the first compression to the sixth compression, there are 5 wavelengths.

• 5λ = 1.50 m

• λ = 1.50 / 5

• λ = 0.30 m

17. A

• First crest to fourth crest = 3 wavelengths.

• 3λ = 0.90 m

• λ = 0.30 m

• v = fλ

• v = 12 × 0.30

• v = 3.6 m/s

18. C

• Period = 0.040 s

• Frequency = 1 / 0.040 = 25 Hz

• v = fλ

• v = 25 × 1.5

• v = 37.5 m/s

• Distance in 2.0 s:

  • distance = speed × time

  • distance = 37.5 × 2.0

  • distance = 75 m

19. B

• 11 consecutive wavefronts contain 10 gaps.

• 10 wavelengths = 5.0 cm

• λ = 0.50 cm = 0.0050 m

• v = fλ

• v = 20 × 0.0050

• v = 0.10 m/s

20. B

• Wavelength = 4.0 cm = 0.040 m

• Wavefronts pass every 0.20 s, so period = 0.20 s.

• v = λ / T

• v = 0.040 / 0.20

• v = 0.20 m/s

---

21. B

• A ray shows the direction of travel of the wave.

• It also shows the direction of energy transfer.

• Rays are drawn perpendicular to wavefronts.

22. B

• The distance between adjacent wavefronts is the wavelength.

• Close wavefronts mean smaller wavelength.

• It does not directly mean greater amplitude.

23. B

• Frequency is determined by the source.

• When a wave enters a new region, frequency stays the same.

• So it remains 12 Hz.

24. A

• Water waves slow down in shallow water.

• Frequency remains unchanged.

• Since v = fλ, if speed decreases and frequency stays the same, wavelength decreases.

• Correct row: speed decreases, wavelength decreases, frequency unchanged.

25. A

• Deep to shallow:

  • speed decreases

  • wavelength decreases

• When entering slower region at an angle, the wave bends towards the normal.

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. D

• Shallow to deep:

  • speed increases

  • wavelength increases

• When entering a faster region at an angle, the wave bends away from the normal.

27. B

• In deep water:

  • v = 0.40 m/s

  • λ = 0.080 m

• Frequency:

  • f = v / λ

  • f = 0.40 / 0.080 = 5.0 Hz

• In shallow water:

  • v = 0.25 m/s

  • λ = v / f

  • λ = 0.25 / 5.0

  • λ = 0.050 m

28. A

• In region X:

  • λ = 6.0 cm = 0.060 m

  • v = 0.30 m/s

• Frequency:

  • f = v / λ

  • f = 0.30 / 0.060 = 5.0 Hz

• In region Y:

  • λ = 4.0 cm = 0.040 m

  • v = fλ

  • v = 5.0 × 0.040

  • v = 0.20 m/s

29. A

• Frequency stays the same at a boundary.

• v = fλ

• If speed decreases and frequency is unchanged, wavelength decreases.

30. C

• v = fλ

• Frequency is unchanged.

• Wavelength increases.

• Therefore speed increases.

31. B

• Law of reflection:

  • angle of incidence = angle of reflection

• Angle of incidence = 35°

• Angle of reflection = 35°

32. D

• Reflection changes the direction of travel.

• Since the wave remains in the same medium:

  • speed stays the same

  • wavelength stays the same

  • frequency stays the same

33. A

• Reflection in the same medium does not change wave speed.

• Source frequency remains unchanged.

• Since v = fλ, wavelength also remains unchanged.

• Correct row: all unchanged.

34. A

• Wavefronts are perpendicular to rays.

• The normal is perpendicular to the barrier.

• The angle between the wavefront and barrier equals the angle between the ray and normal.

• Therefore angle of incidence = 25°.

35. A

• Ray is 60° to the barrier.

• Normal is 90° to the barrier.

• Angle between ray and normal = 90° − 60°

• Angle = 30°

• Reflected ray also makes 30° with the normal.

---

36. C

• Waves spreading after passing through a gap is called diffraction.

37. B

• Diffraction is greatest when the gap size is similar to the wavelength.

• If the gap is much larger than the wavelength, diffraction is much less noticeable.

38. A

• Wavelength = 2.5 cm.

• Gap X = 2.0 cm, which is similar to the wavelength.

• Gap Y = 12 cm, much larger than the wavelength.

• Therefore gap X gives more diffraction.

39. A

• The water depth is unchanged, so wave speed remains unchanged.

• The source frequency remains unchanged.

• Wavelength also remains unchanged, but among the options, the correct unchanged pair is speed and frequency.

• Amplitude may spread out after diffraction.

40. A

• Spreading through a narrow gap is diffraction.

• Since the water depth is unchanged, speed does not decrease because of the gap.

• Frequency also does not increase because of the gap.

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

• In a ripple tank, crests and troughs act like curved lenses.

• They focus and defocus light differently.

• This makes bright and dark wave patterns on the screen.

42. A

• Water depth stays the same, so wave speed stays the same.

• v = fλ

• If frequency increases and speed is unchanged, wavelength decreases.

43. A

• Same water depth means same speed.

• Original speed:

  • v = fλ

  • v = 5.0 × 4.8 cm/s

  • v = 24 cm/s

• New frequency = 8.0 Hz

• New wavelength:

  • λ = v / f

  • λ = 24 / 8.0

  • λ = 3.0 cm

44. A

• Frequency doubles.

• Wave speed stays constant.

• v = fλ, so wavelength halves.

• Amplitude does not automatically change just because frequency changes.

• So amplitude is unchanged and wavelength halves.

45. B

• Frequency doubles.

• Period = 1 / frequency, so period halves.

• Speed unchanged.

• v = fλ, so wavelength halves.

• Correct row: period halves, wavelength halves.

46. A

• Frequency is halved.

• Period = 1/f, so period doubles.

• Speed unchanged.

• v = fλ, so wavelength doubles.

• Correct row: period doubles, wavelength doubles.

47. A

• Wavelength = speed × period

• λ = 0.60 × 0.15

• λ = 0.090 m

48. A

• Initial wave speed:

  • v = fλ

  • v = 25 × 0.080

  • v = 2.0 m/s

• New frequency = 40 Hz.

• Speed unchanged.

• New wavelength:

  • λ = v / f

  • λ = 2.0 / 40

  • λ = 0.050 m

49. A

• Points separated by one wavelength vibrate exactly in phase.

• They have the same displacement and move in the same direction at the same time.

50. C

• A crest and the next trough are separated by half a wavelength.

• Half a wavelength corresponds to a phase difference of 180°.

• One full wavelength corresponds to 360°.

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
Frequency	number of waves per second
Period	time for one wave
Frequency and period	f = 1/T
Wave speed	v = fλ
Crest to fifth crest	4 wavelengths, not 5
Compression to sixth compression	5 wavelengths
Crest-to-trough distance	2 × amplitude
Transverse wave	vibration perpendicular to travel
Longitudinal wave	vibration parallel to travel
Sound in air	longitudinal
Electromagnetic waves	transverse
Waves transfer	energy, not matter overall
Ray	direction of energy transfer
Wavefront spacing	wavelength
Boundary crossing	frequency unchanged
Deep to shallow water	speed decreases, wavelength decreases
Shallow to deep water	speed increases, wavelength increases
Slower medium	bends towards normal
Faster medium	bends away from normal
Reflection	angle of incidence = angle of reflection
Same medium reflection	speed, frequency, wavelength unchanged
Diffraction	spreading through gap
Maximum diffraction	gap similar to wavelength
Frequency doubled, speed same	wavelength halves
Frequency halved, speed same	wavelength doubles
One wavelength separation	in phase
Crest to next trough	180° phase difference