Sound and waves

Question 1

Define transverse wave.

Answer 1

The direction in which the energy travels is perpendicular to the direction of vibration of the particles of the medium.

Question 2

Define longitudinal wave.

Answer 2

The direction in which the energy travels is parallel to the direction of vibration of the particles of the medium.

Question 3

Define wavelength.

Answer 3

The distance between two successive compressions.

Question 4

Can transverse or longitudinal waves be polarised?

Answer 4

Transverse waves can, longitudinal waves cannot be.

Question 5

When a vibrating tuning fork touches a table top why does the sound appear louder?

Answer 5

As the table top is forced to vibrate at the same frequency as the tuning fork.

Question 6

Define diffraction.

Answer 6

The spreading of a wave front into the geometrical shadow when it passes through a gap or around an obstacle.

Question 7

Explain pitch.

Answer 7

Pitch is related to the frequency of a sound. The higher the frequency the higher the pitch.

Question 8

Explain loudness.

Answer 8

The loudness of a sound depends on the amplitude of the vibration of the sound wave.

Question 9

What are the characteristics of sound? (Three ways in which sound differ)

Answer 9

• Pitch
• Quality
• Loudness

Question 10

Explain quality.

Answer 10

Depends on the number and intensity of the harmonics (overtones) present.

Question 11

What are the two classifications of waves?

Answer 11

• Mechanical waves

- Electromagnetic waves

Question 12

When is the diffraction more noticeable?

Answer 12

When the size of the gap or obstacle os approximately equal to or less than the wavelength of the wave.

Question 13

What is used to demonstrate diffraction of light waves?

Answer 13

A diffraction grating.

Question 14

Do sound waves have difficulty diffracting?

Answer 14

No they easily diffract.

Question 15

Define interference.

Answer 15

Will occur when waves from coherent sources meet and combine.
Constructive interference gives a wave of great amplitude.
Destructive interference give a wave of smaller amplitude.

Question 16

What is the condition for constructive interference?

Answer 16

When the waves meet they are in phase and the waves have the same frequency. The crest of one wave meets the crest of the other wave.

Question 17

Explain coherent sources.

Answer 17

Coherent sources emit waves of the same frequency and the waves are in phase or have a constant phase difference.

Question 18

What is the condition for destructive interference?

Answer 18

When the waves meet they are out of phase with a path difference of λ/2 or a multiple of this. The crest of one wave meets the trough of the other wave.

Question 19

When are waves ‘in phase’?

Answer 19

When they are doing the same thing.

Question 20

What is the wavelength of the stationary wave?

Answer 20

Twice the distance between successive nodes or successive antinodes.

Question 21

Define the doppler effect.

Answer 21

The apparent change in the frequency of a wave due to the relative motion between source and observer.

Question 22

Give two uses of the Doppler effect.

Answer 22

• Blood flow measurement

- Checking the heart beat of a foetus.

Question 23

Explain natural frequency.

Answer 23

When a system that is capable of vibrating is made to vibrate it will do so at its natural frequency.

Question 24

Explain forced frequency.

Answer 24

When an external vibration force acts on a system that is capable of vibrating the external force provides the forced frequency.

Question 25

What are harmonics?

Answer 25

Multiples of the fundamental mode of vibration.

Question 26

Demonstration to show refraction of sound.

Answer 26

• The speaker connected to the signal generator emits sound in all directions.
• Some of this sound if refracted by the balloon of CO2 gas and is concentrated at a point.
• This sound energy is picked up by the microphone and displayed on the oscilloscope.