# Physics (P1) - Waves

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• Created by: Roma
• Created on: 13-12-13 20:39
What are waves used for?
To transfer energy and information.
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How do transverse waves tavel?
The oscillation (vibration) of the particles is perpendicular (at right angles) to the direction in which the wave travels.
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How do longitudinal waves tavel?
The oscillation (vibration) of the particles is parallel to the direction of the wave. They have compressions and rarefactions.
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What are electromagnetic waves and give examples of them?
Transverse waves that can travel through a vacuum due to having no moving particles as they are in electric and magnetic fields. E.g. light and radio waves.
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What are mechanical waves and give an example of one?
Transverse of longitudinal waves that travel through a substance. E.g. sound waves (longitudinal).
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What is the amplitude of a wave?
The height of the wave crest or the depth of the wave trough from rest position.
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What is the wavelength of a wave?
Transverse - the distance from crest to crest or trough to wave . Longitudinal - the distance from the middle of one rarefaction to the next, or the middle of one compression to the next.
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What is the frequency (hertz) of a wave?
The number of wave crests/compressions passing a point in one second.
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What is the incident ray?
The ray that goes towards the mirror.
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What is the reflected ray?
The ray is coming away from the mirror.
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What is the normal?
A line perpendicular to the mirror at the point where the incident ray hits the mirror.
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What is the angle of incidence?
The angle between the incident ray and the normal.
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What is the angle of reflection?
The angle between the reflected ray and the normal.
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What is the relation between the angle of incidence and the angle of reflection?
They are equal.
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What is the image in a plane mirror?
The same size as the original object, upright, the same distance behind the mirror as the original object, virtual.
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What is a real image?
One that can be formed on a screen, because the rays of light that produce the image actually pass through it.
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What is a virtual image?
One that cannot be formed on a screen, because the rays of light that produce the image, do not actually pass through it.
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What do waves do when the cross a boundary between different substances?
They change speed, the wavelength change, but the frequency stays the same.
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What is refraction?
The change of direction of all waves (inc. light and sound) when it crosses a boundary between two substances.
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What does change in speed of waves cause?
A change in direction of the waves.
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What happens when light enters a more dense substance?
It slows down and the ray changes direction towards the normal.
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What happens when light enters a less dense substance?
It speeds up and the ray changes direction away from the normal.
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What happens if a light ray travelling along the normal crosses a boundary between different substances?
It will not change direction.
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What is dispersion?
When a ray of white light is shone onto a triangular glass prism and we can see the spectrum being produced, because different colours of light have different wavelengths are are refracted by slightly different amounts.
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Which colours are refracted the most and the least?
Violet is refracted the most, and red the least.
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What is diffraction?
The spreading out of waves (inc. light and sound) when they pass through a gap or round the edge of an obstacle.
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When is diffraction most noticeable/greater?
The wavelength is the same size as the gap or the obstacle/the gap is narrow.
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It the radio waves don't diffract enough when they go over hills.
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What are sound waves?
Longitudinal waves caused by mechanical vibrations in a substance. They can travel through all three states of matter (fastest in solids and slowest in gases), but cannot travel through a vacuum.
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How can you test that sound waves cannot travel through a vacuum?
Listening to a ringing bell in a bell jar, and as the air is pumped out, the sound fades away.
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What range of frequencies can be heard by humans?
20Hz - 20 000Hz.
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What is the reflection of sound waves?
Echoes.
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What conditions are best for echoes?
Hard, flat surface, as soft things will absorb the sound instead of reflecting it.
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What else can sound do apart from reflect?
They can be refracted at the boundaries between layers of air at different temperatures, and also diffracted,
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What does pitch depend on?
Frequency. The higher the frequency of the wave, the higher the pitch of the sound.
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What does loudness depend on?
Amplitude. The greater the amplitude, the more energy the waves carry and so the louder the sound.
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Where can different waveforms be shown?
An oscilloscope.
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Why do instruments sound different?
The quality of a note depends on the waveform. Different instruments produce different waveforms.
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## Other cards in this set

### Card 2

#### Front

How do transverse waves tavel?

#### Back

The oscillation (vibration) of the particles is perpendicular (at right angles) to the direction in which the wave travels.

### Card 3

#### Front

How do longitudinal waves tavel?

### Card 4

#### Front

What are electromagnetic waves and give examples of them?

### Card 5

#### Front

What are mechanical waves and give an example of one?