# P1 Waves

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• Created by: frabadaba
• Created on: 06-05-16 16:35

## Waves

Waves transfer energy from one place to another without transfering matter.

The amplitude of a wave is the distance from the rest position to a crest (peak).  The wavelength is the length of a full cycle, one crest to another.  The frequency is the number of complete waves passing a certain point per second; it's measured in Hz, hertz.

Transverse waves vibrate sideways: they're usually light, ripples and waves.  The vibrations are perpendicular to the direction of energy transfer.

Longituudinal waves vibrate along the same line; they're usually sound, ultrasound and shock waves.  The vibrations are parallel to the direction of energy transfer.

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## Wave Properties

Obstacles can change a wave's direction of travel by reflection, refraction or diffraction.

Reflection of light allows use to see object as light bounces off of objects.  Light reflects off even surfaces at the same angle it approaches, but if the surface is uneven light reflects off at different angles.

The angle of incidence = the angle of reflection

Ray diagrams illustrate how light is laterally reflected in mirrors.

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## Refraction

Refraction is when the speed of a wave changes so the direction changes too.

When a wave crosses a boundry it changes direction since the rays which aren't reflected pass through a new medium at an angle.  If they're travelling along the normal (angle of incidence = 0) then the ray will only change speed and will not refract.

The different densities in the boundies cause the change in speed.

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## Diffraction

Diffraction is when waves spread out.

Waves diffract at the edges when they through a gap.  The amount of diffraction is at maximum when the gap is the same as the wavelength.  Diffraction is poor when the gap is much wider than the wave length; when the gap is a bit wider than the wavelength the wave only diffracts at the edges.

An example of diffraction is between air and glass or air and water.

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## Electromagnetic Waves

Electromagnetic waves (EM Waves) have different wavelengths/frequencies, so they have different properties.

They're grouped with increasing frequencies and energy (decreasing wavelength) from left to right.

X-rays and gamma rays have ionising radiation which is dangerous as they can kill living cells or cause them to become cancerous.  All different types of EM waves travel at the same speed in a vaccum like space.

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## EM Wave Uses

Different electromagnetic waves have different properties like their frequency, making them suitable for different purposes.

Radio waves are used for communication.  Long-wave radio can be transmitted across the world as they diffract around the curved surface of the earth; or hills and tunnels.  Short radio waves are used for TV and FM radio transmissions; they can travel long distances as they're reflected from the ionosphere (an electrically charged layer in the earth's atmosphere) as well as medium-wave signals.

Microwaves are used for satellite communication and mobiles, which can pass through the earth's watery atmosphere unlike radiowaves.  They use remote-sensing transmitters in space to recieve the signal.  However some of the microwaves are absorbed by water, which heats the water up: but if the water is in your cells people view this a cause for concern without conclusive evidence.

Infared waves are used for remote controls by emitting out different patterns of infared waves for different commands.  Optial fibres also use infared waves to carry data rapidly over log distances.  The signal is carried as pulses of light or infared radiation as it's reflected off of the sides of a narrow core - from one end of the wire to the other.

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## Sound Waves

Sound travels as longditudinal waves due from vibrating objects as a series of compressions.

Sound travels faster in solids than in liquids due to the denser particle arrangement.  Sound cannot travel in space as space is a vaccum so there are no particles to vibrate.

Sound waves can be reflected by hard, flat surfaces.  When there are objects in a room they absorb the sound quickly - reducing echoes (echoes are reflected sound waves).  There's a delay between the original sound and the echo due to the echo needing to travel further.  Sound waves refract (change direction) when they enter a new media.  The denser the media the faster the wave travels.

High frequency means a high pitch and the bigger the amplitude the louder the wave.

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