Waves

Question 1

For what do we use waves?

What is the significance of the direction of travel of the wave?

Answer 1

We use waves to transfer energy and information, the direction of travel of the wave is the direction in which it transfers energy.

Question 2

What is a transverse wave?

Answer 2

For a transverse wave the oscillation of the particles is perpendicular to the direction in which the wave travels.

Question 3

What is a longitudinal wave?

Answer 3

For a longitudinal wave the oscillation of particles is parallel to the direction of travel of the wave.
A longitudinal wave is made up of compressions and rarefactions.

Question 4

Through what can all electromagnetic waves travel?
What is special about electromagnetic waves?
Why are electromagnetic waves transverse?
Give two example of electromagnetic waves?

Answer 4

They can all travel through a vacuum. There are no particles moving in an electromagnet wave, as these waves are oscillations in electric and magnetic fields. The oscillations are perpendicular to the direction of travel of the wave, so all electromagnetic waves are transverse waves.
Light waves and radio waves.

Question 5

What are mechanical waves? Give two examples.

What type of wave are sound waves?

Answer 5

Waves that travel through a medium such as waves on springs and sound waves, mechanical waves may be longitudinal or transverse.
Longitudinal waves.

Question 6

What is the amplitude of a wave?

What is the relationship between the amplitude of a wave and the amount of energy it carries?

Answer 6

The amplitude of a wave is the height of the wave crest or the depth of the wave trough from the position at rest.
The greater the amplitude of a wave the more energy it carries.

Question 7

What is the wavelength of a wave?

Answer 7

The wavelength of a wave is the distance from one crest to the next crest, or from one trough to the next trough.

Question 8

What is the frequency of a wave?

What is the unit of frequency?

Answer 8

The frequency of a wave is the number of wave crests passing a point in one second, the unit of frequency is the hertz (Hz).

Question 9

How can the speed of a wave be calculated?

What equation does this?

Answer 9

The speed of a wave can be calculated by multiplying the frequency of the wave in Hz by the wavelength in m.
v= f x lambda
v is the speed, m/s
f is the frequency, Hz
lambda is the wavelength, m

Question 10

What is the wavelength of a longitudinal wave?

Answer 10

The distance from the middle of one wave compression to the middle of the next compression.

Question 11

What is the frequency of a longitudinal wave?

Answer 11

The number of compressions passing a point in one second.

Question 12

What is the angle of incidence?
What is the angle of reflection?
What is the relationship between the angle of incidence and the angle of reflection?

Answer 12

The angle of incidence is the angle between the incident ray and the normal.
The angle of reflection is the angle between the reflected ray and the normal.
For any reflected ray the angle of incidence is equal to the angle of reflection.

Question 13

Give four ways to describe the image in a plane mirror.

Answer 13

1) The image is the same size as the object.
2) The image is upright.
3) The image is the same distance behind the mirror as the object is in front.
4) The image is virtual.

Question 14

What is a real image?

What is a virtual image?

Answer 14

A real image is one that can be projected on a screen because the rays of light that produce the image actually pass through it.
A virtual image cannot be formed on a screen because the rays of light that produce the image, only appear to pass through it.

Question 15

How is the image in a mirror produced?

Answer 15

The image is seen in a mirror due to the reflection of light.

Question 16

What happens to waves when they cross a boundary between different substances?

Answer 16

The wave changes speed, and the wavelength of the wave also changes, but the frequency remains the same.

Question 17

What is refraction?

What causes the change in direction?

Answer 17

Refraction is the change of direction of a light ray when it passes across a boundary between two transparent substances.
The change in direction is caused by the change in the waves speed as it crosses the boundary.

Question 18

What happens when light enters a more dense substance what happens to the ray?
Give one example of when light enters a more dense substance?

Answer 18

When light enters a more dense substance it slows down and bends towards the normal.

Air to glass

Question 19

What happens when light enters a less dense substance what happens to the ray?
Give one example of when light enters a less dense substance?

Answer 19

When light enters a less dense substance it speeds up and bends away from the normal.

Glass to air

Question 20

If a light ray is travelling along a normal what will happen when it crosses a boundary?

Answer 20

A light ray travelling along the normal will not change direction when it crosses a boundary.

Question 21

What happens when white light is shone onto a triangular glass prism?
What is this called?
Which colour light is refracted the most and which colour light is refracted the least?

Answer 21

A spectrum is produced and we can see that different colours of light are refracted by slightly different amounts, this is because different colours have different wavelengths.
This is called dispersion.
Violet light is refracted the most and red light is refracted the least.

Question 22

What is diffraction?

When is the effect of diffraction most noticeable?

Answer 22

It is the spreading of waves when they pass through a gap or round an obstacle.
The effect is most noticeable when the wavelength of the waves is about the same size as the gap or the obstacle..

Question 23

What type of waves carry Tv signals?
Why may people living in hilly areas receive no signal at all?
What happens to waves passing a hill how might this affect the signal?

Answer 23

Tv signals are carried by radio waves, people living in hilly areas may not be able to receive a signal because it is blocked by a hill. Radio waves passing the hill will be diffracted round the hill, if they do not diffract enough the radio and Tv signals will be weak.

Question 24

What is sound caused by and how does it travel?
What substances do sound waves travel fastest and slowest in?
What are sound waves unable to travel through?

Answer 24

Sound is caused by mechanical vibrations in a substance and travels as a wave.
Sound waves travel fastest in solids and slowest in gases.
Sound waves are unable to travel through a vacuum, e.g. space.

Question 25

What type of wave are sound waves and what does this mean about the vibrations and direction of which the wave travels?

Answer 25

Sound waves are longitudinal waves, which means the vibrations occur is the same direction as the direction of travel of the wave.

Question 26

What is the range of frequencies that can be heard by the human ear?
How is this affected by age?

Answer 26

The range of frequencies that can be heard by the human ear is from 20Hz to 20,000 Hz.
The ability to hear the higher frequencies declines with age.

Question 27

What is produced when sound waves are reflected?
What type of surfaces reflect sound?
What things absorb sound?
Why does a furnished room sound different from an empty room?

Answer 27

Echoes
Only, hard flat surfaces such as flat walls and floors reflect sound.
Soft things such as carpets, curtains and furniture absorb sounds.
As furnishings such as carpets, curtains and furniture absorb the sound.

Question 28

Sound waves can be refracted, where does the diffraction take place?
Sound waves can also be diffracted.

Answer 28

Refraction takes place at the boundaries between layers of air at different temperatures.

Question 29

What is the relationship between the pitch of a note of a musical instrument and the frequency of the wave?

Answer 29

The higher the frequency of the wave, the higher the pitch of the note.

Question 30

What is the relationship between the loudness of a sound and the amplitude of a wave?

Answer 30

The greater the amplitude, the more energy the wave carries and the louder the sound.

Question 31

What does an oscilloscope show?

What instruments produce ‘pure’ waveforms?

Answer 31

Differences in wave form.

Tuning forks and signal generators.

Question 32

On what does the quality of a note depend?

Why do different instruments sound different from each other?

Answer 32

The waveform

Different instruments sound different from each other because they produce different waveforms.

Question 33

What produces sound waves when an instrument is played?

Answer 33

Vibrations created in an instrument when it is played produce sound waves.

Question 34

In what three ways can sound be produced in an instrument? Give one example of an instrument that uses each different type of sound production.

Answer 34

In some instruments a column of air vibrates, e.g. a saxophone
In some instruments a string vibrates, e.g. a violin
Some instruments vibrate when they are struck, e.g. a xylophone.