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Waves Flashcards

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1
Q

What is a wave?

A

A wave is a disturbance through a medium that transfers energy from one point to another without causing any permanent displacement of the medium itself.

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2
Q

Give three examples of situations where waves can be seen.

A

Waves can be seen when a stone is thrown into water, when oscillating a spring, and when a rope is fixed at one end and jerked at another end.

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3
Q

What are the two classes of waves?

A

The two classes of waves are mechanical waves and electromagnetic waves.

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4
Q

What are mechanical waves?

A

Mechanical waves are waves that require a material medium to transfer energy from one point to another and are produced by vibrating bodies.

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5
Q

Can mechanical waves travel through a vacuum?

A

No, mechanical waves cannot travel through a vacuum.

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6
Q

Do mechanical waves normally have a high or low velocity?

A

Mechanical waves normally have a low velocity.

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7
Q

Give three examples of mechanical waves.

A

Examples of mechanical waves include sound waves, water waves, and waves in stretched strings.

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8
Q

What are electromagnetic waves?

A

Electromagnetic waves are waves that do not require a material medium to transfer energy and are produced by varying electric and magnetic fields.

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9
Q

Can electromagnetic waves travel through a vacuum?

A

Yes, electromagnetic waves can travel through a vacuum.

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10
Q

At what speed do all electromagnetic waves travel?

A

All electromagnetic waves travel at the speed of light, which is (3 \times 10^8 \, \text{m/s}).

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11
Q

Give six examples of electromagnetic waves.

A

Examples of electromagnetic waves include gamma rays, X-rays, radio waves, infrared, visible light, and ultraviolet (UV) light.

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12
Q

How are waves normally represented?

A

Waves are normally represented in the form of oscillations or cycles.

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13
Q

What is an oscillation?

A

An oscillation is a complete to and fro movement of a wave.

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14
Q

What is the rest position of a wave?

A

The rest position is the undisturbed position of a wave.

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15
Q

What is amplitude?

A

Amplitude is the maximum displacement of a wave particle from the rest position.

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16
Q

What is a crest in a wave?

A

A crest is the maximum displacement of a wave above the rest position.

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17
Q

What is a trough in a wave?

A

A trough is the maximum displacement of a wave below the rest position.

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18
Q

What is wavelength?

A

Wavelength is the distance between two successive crests or troughs of a wave or the distance covered in one complete oscillation/cycle. Wavelength is measured in meters.

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19
Q

What is the period of a wave?

A

The period, (T), is the time taken to complete one oscillation and is measured in seconds.

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20
Q

What is frequency?

A

Frequency, (f), is the number of oscillations per second and is measured in Hertz (Hz).

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21
Q

What is the wave phase?

A

Wave phase refers to the timing of one oscillation of a wave in comparison with another oscillation of another wave. Wave particles are in phase if they are exactly at the same point at the same time, at the same distance from the rest position, and are moving in the same direction.

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22
Q

What is the velocity of a wave?

A

The velocity of a wave is the distance traveled by the wave per unit time.

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23
Q

How is the velocity of a wave calculated?

A

The velocity of a wave, (v), is calculated as the product of its wavelength, (\lambda), and frequency, (f). The formula is (v = \lambda \times f).

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24
Q

What is the formula for the period of a wave?

A

The formula for the period of a wave is (T = \frac{1}{f}).

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25
Q

What is the formula for frequency when the period is known?

A

The formula for frequency is (f = \frac{1}{T}).

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26
Q

How do you calculate the period if the number of oscillations, (n), is known?

A

The period is calculated using the formula (T = \frac{t}{n}), where (t) is the time taken for (n) oscillations.

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27
Q

What assumption is made for calculating the speed of radio waves?

A

The assumption made is that radio waves are electromagnetic waves, so they travel at the speed of light ((3 \times 10^8 \, \text{m/s})).

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28
Q

How do you calculate the wavelength when the distance between successive crests or troughs is known?

A

Wavelength, (\lambda), is calculated as (\lambda = \frac{d}{n - 1}), where (d) is the distance and (n) is the number of successive crests or troughs.

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29
Q

What is a ripple tank used for?

A

A ripple tank is used to study the properties of water waves.

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30
Q

What does a ripple tank contain?

A

A ripple tank contains a transparent glass trough filled with water.

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31
Q

How are wave images formed in a ripple tank?

A

The images of the waves are formed on a white screen placed below the tank.

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32
Q

What illuminates the ripple tank for wave observation?

A

The ripple tank is illuminated with a source of light (lamp).

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33
Q

How are waves produced in a ripple tank?

A

Waves are produced by means of a dipper that hits the surface of the water. The dipper is vibrated by an electric motor.

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34
Q

What does a stroboscope do in a ripple tank?

A

The stroboscope helps to make the waves stationary for better study.

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35
Q

What type of wave fronts are produced by a spherical dipper in a ripple tank?

A

Circular wave fronts are produced.

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36
Q

What type of wave fronts are produced by a straight rod dipper in a ripple tank?

A

Plane wave fronts are produced.

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37
Q

What is reflection of waves?

A

Reflection is the bouncing off of waves when they meet a barrier.

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38
Q

How are plane wave fronts reflected on a plane surface?

A

Plane wave fronts are reflected as plane wave fronts.

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39
Q

What happens to plane wave fronts when they are reflected on a concave reflector?

A

They are reflected as concave wave fronts.

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40
Q

What happens to plane wave fronts when they are reflected on a convex reflector?

A

They are reflected as convex wave fronts.

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41
Q

What happens to concave circular wave fronts when they are reflected on a plane surface?

A

They are reflected as convex wave fronts.

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42
Q

How are convex circular wave fronts reflected on a plane surface?

A

They are reflected as concave wave fronts.

43
Q

What is refraction of waves?

A

Refraction is the change in direction of a wave as it moves from one medium to another of different depth.

44
Q

What changes occur when waves move from deep water to shallow water?

A

Wavelength decreases, speed decreases, and waves bend towards the normal. Frequency remains constant.

45
Q

What changes occur when waves move from shallow water to deep water?

A

Wavelength increases, speed increases, and waves bend away from the normal. Frequency remains constant.

46
Q

How is the refractive index of water calculated?

A

The refractive index is calculated as the ratio of the velocity of waves in deep water to the velocity in shallow water.

47
Q

What is diffraction of waves?

A

Diffraction is the spreading of waves as they pass through holes, around corners, or edges of an obstacle.

48
Q

What happens when the gap between two barriers is small in a ripple tank?

A

Plane wave fronts spread out into a circular shape.

49
Q

What happens when the gap between two barriers is wide in a ripple tank?

A

Plane wave fronts emerge slightly bent at the edges.

50
Q

Why is sound heard in corners but light isn’t?

A

Sound waves are more diffracted than light waves because sound waves have longer wavelengths.

51
Q

Why does the sky appear red during sunrise or sunset?

A

Blue light scatters away easily during sunrise/sunset, leaving only light of longer wavelengths, which is red.

52
Q

Why does the sky appear blue during the day?

A

Blue light, with its short wavelength, scatters in all directions, giving the sky its blue appearance.

53
Q

What is constructive interference?

A

Constructive interference occurs when a crest of one wave meets a crest of another, or a trough of one wave meets a trough of another, forming a wave with greater amplitude.

54
Q

What is destructive interference?

A

Destructive interference occurs when a crest of one wave meets a trough of another, forming a wave with no amplitude.

55
Q

What conditions are required for interference to occur?

A

The two waves must have the same frequency, speed, wavelength, amplitude, and be moving in the same direction.

56
Q

What is reverberation?

A

Reverberation is the prolonged sound due to multiple reflections.

57
Q

Where does reverberation typically occur?

A

Reverberation occurs in large halls with many reflecting surfaces or walls.

58
Q

What is the effect of reverberation on sound in terms of duration?

A

Reverberation causes sound to last longer and appear as if it is prolonged.

59
Q

If the time taken to hear the echo is less than 0.1s, what can the human ear distinguish?

A

The human ear cannot distinguish between the original sound and the echo.

60
Q

What happens if the time to hear the echo is 0.1s?

A

The original sound appears to be prolonged, resulting in reverberation.

61
Q

What is one advantage of reverberation?

A

Reasonable reverberation makes speeches audible.

62
Q

What is a disadvantage of excessive reverberation?

A

Unreasonable reverberation produces disorganized sound, making it unclear.

63
Q

How can reverberation in large halls be minimized?

A

By using sound absorbing materials such as soft boards, curtains, carpets, and cushioning seats.

64
Q

Why does reverberation time decrease in a church when it is filled with people?

A

Human bodies and clothes absorb sound, reducing reverberation compared to an empty church.

65
Q

What causes refraction of sound waves?

A

Refraction occurs when the speed of sound waves changes as they cross the boundary between two media.

66
Q

How does sound wave refraction during the day affect sound clarity?

A

Sound waves are refracted away from the ground, making sound harder to hear during the day.

67
Q

Why are radio signals less clear during the day?

A

Because sound waves are refracted away from the ground, affecting signal clarity.

68
Q

How does refraction of sound waves during the night differ from during the day?

A

At night, sound waves are refracted towards the ground, making sound easier to hear.

69
Q

What is the primary difference between sound waves and light waves?

A

Sound waves are longitudinal and mechanical, while light waves are transverse and can travel through a vacuum.

70
Q

What is a musical sound?

A

A musical sound is produced by regular and uniform vibrations.

71
Q

What is pitch in musical sounds?

A

Pitch is the loudness or softness of a sound, dependent on its frequency.

72
Q

What affects the loudness of a sound?

A

Loudness depends on the amplitude of the sound, the sensitivity of the ear, and the intensity of sound.

73
Q

How is quality or timbre of a sound determined?

A

Quality or timbre is determined by the frequency and amplitude of a note, including the number of overtones.

74
Q

How does increasing the length of a vibrating string affect its frequency?

A

Increasing the length decreases the frequency of the note produced.

75
Q

What happens to the frequency of a string if the tension is increased?

A

Increasing the tension increases the frequency of the note produced.

76
Q

What is the relationship between the thickness of a string and the frequency of the sound it produces?

A

Thin strings produce higher frequency notes, while thick strings produce lower frequency notes.

77
Q

What are nodes in a stationary wave?

A

Nodes are points where the wave particles are at rest, and the amplitude is zero.

78
Q

What are antinodes in a stationary wave?

A

Antinodes are points where the wave particles have maximum displacement and amplitude.

79
Q

What is the distance between two successive nodes or antinodes?

A

The distance is equal to half the wavelength (𝜆/2).

80
Q

What conditions are necessary for stationary waves to form?

A

The waves must have the same frequency, speed, wavelength, amplitude, and move in opposite directions.

81
Q

What is the fundamental frequency of a musical note?

A

It is the frequency of the fundamental note, which is the lowest audible note produced.

82
Q

What is an overtone?

A

An overtone is a note whose frequency is higher than the fundamental frequency.

83
Q

What is an octave in terms of frequency?

A

An octave is the interval between one note and another note with half or double its frequency.

84
Q

How does the frequency of a note four octaves above 20Hz compare to the original?

A

The frequency is 320Hz.

85
Q

If the length of a string is increased from 0.75m to 1m, what happens to the frequency of a note?

A

The frequency decreases from 200Hz to 150Hz.

86
Q

What is the fundamental frequency if the second harmonic frequency is 600Hz?

A

The fundamental frequency is 300Hz.

87
Q

What type of pipes are used in the study of waves produced in pipes?

A

Closed pipes and open pipes.

88
Q

What is the fundamental frequency in a closed pipe for the 1st harmonic?

A

( f_1 = \frac{V}{4L} ), where ( L = \frac{1}{4} \lambda ).

89
Q

How is the wavelength (( \lambda )) of the 3rd harmonic in a closed pipe related to its length (L)?

A

( \lambda = \frac{4L}{3} ).

90
Q

What is the frequency of the 3rd harmonic (( f_3 )) in a closed pipe in terms of the fundamental frequency (( f_1 ))?

A

( f_3 = 3f_1 ).

91
Q

How does the wavelength (( \lambda )) of the 5th harmonic in a closed pipe relate to the length of the pipe (L)?

A

( \lambda = \frac{4L}{5} ).

92
Q

What harmonics are produced by closed pipes?

A

Only odd harmonics (e.g., ( f_1, 3f_1, 5f_1, \ldots )).

93
Q

For an open pipe, what is the wavelength (( \lambda )) of the fundamental frequency (1st harmonic) in relation to the length of the pipe (L)?

A

( \lambda = 2L ).

94
Q

What is the relationship between the frequency of the 2nd harmonic (( f_2 )) and the fundamental frequency (( f_1 )) in an open pipe?

A

( f_2 = 2f_1 ).

95
Q

How is the wavelength (( \lambda )) of the 3rd harmonic in an open pipe related to its length (L)?

A

( \lambda = \frac{2L}{3} ).

96
Q

What harmonics are produced by open pipes?

A

Both odd and even harmonics (e.g., ( f_1, 2f_1, 3f_1, 4f_1, \ldots )).

97
Q

Why are open pipes preferred over closed pipes in making music?

A

Open pipes produce high-quality sound because they produce both odd and even harmonics.

98
Q

If the frequency of the 3rd harmonic in an open pipe is 750 Hz and the length of the pipe is 0.8 m, what is the speed of sound?

A

The speed of sound is 400 m/s.

99
Q

In a closed pipe with a length of 10 cm, what is the fundamental frequency if the speed of sound is 340 m/s?

A

The fundamental frequency is 850 Hz.

100
Q

For a pipe open at both ends with a length of 40 cm, what is the frequency of the fundamental note if the speed of sound is 340 m/s?

A

The frequency of the fundamental note is 425 Hz.

101
Q

What is the frequency of the 4th overtone (5th harmonic) in an open pipe if its length is 0.4 m and the frequency is 900 Hz?

A

The frequency of the fundamental note is 180 Hz.

102
Q

What is resonance?

A

Resonance occurs when a body is set into vibrations at its own natural frequency by another nearby body vibrating at the same frequency, resulting in stronger vibrations with a greater amplitude.

103
Q

Give an example of resonance in daily life.

A

Shaking of window glasses as a heavy vehicle passes by, or breaking a wine glass by an opera singer’s sound.

Physics (7 decks)

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