# P6 - OCR 21st Century Physics Wave model of radiation

P6 - OCR 21st Century Physics Wave model of radiation.

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• Created by: bhiruntha
• Created on: 28-01-12 19:32

## Waves –The Basics

Waves have amplitude, wavelength and frequency.

• Frequency is the number of waves passing past a certain point per second or the number of waves produced by a source each second. It’s measure in hertz (Hz). 1 Hz is 1 wave per second.
•  Transverse waves have sideways vibrations

Most waves are transverse:

•  All EM waves (light ect),    Ripples on water,  Waves on strings , A slinky wiggled up and down.

In transverse waves the vibrations are at 90° to the direction of the wave.

Longitudinal waves have vibrations along the same line.

• Sound and ultrasound, Shock waves (seismic waves) , A slinky spring, when you push the end.

Wave speed = Frequency x Wavelength

V = Wave speed (m/s),   F = Frequency (Hz), Squiggle = Wave length (m)

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## Wave Properties

·         When a wave hits a material all waves can be reflected, refracted (through material but change direction) and diffracted (bends round making it spread out).

·         Reflection

•    Angle of incidence = Angle of reflection
•    When a wave hits a boundary between one medium and another, some is always reflected.
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## Wave properties Part 2

·        Refraction – Waves change speed and direction.

•    Waves travel at different speeds in substances of different densities.
•    EM waves normally travel slower in denser mediums, sounds waves travel faster.
•    If they hit a boundary straight on, they go straight on; if they hit it at an angle they change direction.
•   The reason it goes in and turns, and then comes back out in the same direction is because it bends towards the normal when entering a more dense material, and then bends back when into a less dense material, so it ends up in the same direction (if the materials are the same).
•  Waves have the same change in speed and wavelength, so the frequency doesn’t change.
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## Wave Properties Part 3

•      Total internal reflection happens above the critical angle.
•    When a light wave travels from a dense substance like glass or water into a less dense subject like air, its angle of refraction is greater than the angle of incidence.
•    If something going from air to glass, hits the glass at 42° or above, total internal reflection takes place, and non is refracted at all.
•   This happens in wires and things.
•          Diffraction – Waves spreading out
•    All waves spread out (diffract) at the edges when they pass through a gap or past an object.
•    The amount of diffraction depends on the size of the gap relative to the wavelength of the wave.
•    The longer the wavelength and narrower the gap the more the wave spreads out.
•   A narrow gap depends on the size of the wavelength.
•    A narrow gap is about the same size of the wavelength in question.
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## Wave interference

·         When waves meet they cause disturbance.

• When waves are in step you add the placement, when they aren’t you subtract it.
• Interference of light makes bright and dark patches.
• Constructive interference makes it bright, destructive interference makes it dark.

Light and sound must be waves because :

•    They can diffracted (bend around an object)
•    Reflected
•   Absorbed
•   Transmitted
•    If light acted like particles there wouldn’t be any positive or negative disturbance, they wouldn’t interfere.
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## Electromagnetic Waves

Rabbits (radio waves) Mate (microwaves) In (infra-red) Very (visible) Unusual (unltraviolet) eXpensive (X-rays) Gardens (gamma rays).

•   As you go → the frequency increases (so does energy)
•    And as you go ← the wavelength increases.
•    All waves travel at 300,000,000 (300million) m/s in a vacuum.
• Even different colours of light have the different wavelength
•   Sounds waves can’t travel through a vacuum.
•    Sound waves are transmitted by vibrating particles.  So no particles in a vacuum, so no sound.
•   The energy of a photon depends on a frequency of EM waves.
•    Energy delivered by each photo depends on the frequency of the EM waves.
• The higher the frequency, the higher the energy the photon delivers.   Intensity depends on the number of photons per second.
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## Uses of EM waves

• Radio waves- Communication - long distances, dont get absorbed by atmosphere.
• Used for TV and FM radio ( short wavelength compared to normal radio waves)
• Microwaves Satellite communication - passes through atmosphere easily
• absorbed by sat. receivers well which sends it back to earth to be absorbed by a satellite on the ground .
• Ovens, pass through moist atmosphere but are absorbed by water.
• X-Rays - identify fractures . Bones absorb it, flesh doesnt. Where it goes through, the plate turns back, and bones stay white.
• Infrared and light - Optical fibres - The single fibre doesnt weaken much and carry a lot of information.

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## Analogue and Digital Signals

•  Analogue signals vary. Digitals either on or off.
•   The amplitude or frequency of an analogue signal varies continuously; it could be any value in a particular range.
•    Digital signals are pulses.
•    A digital receiver will decode the pulses to get a copy of the original signal.
•  Signals have to be amplified.
• They weaken as they travel. So they are amplified on their route.
• They also pick up interference.
•   Digital signals are far better quality.
• Its easier to clean up a signal that only consists of like 2 different possibilities, than one with a large range.
• So digital signals have a much higher quality sound.
•  Digital signals can be processed by computers too.
•   You can send more than one signal at once with digital signal.
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## Information and waves

•   Information is converted into signals.
•  2 waves you can send information as waves, AM and FM.
•    AM radio waves have varying amplitude.
•  An AM radio transmitter sends out a continuous carrier wave.
•  This signal is the superimposed on the carrier wave using amplitude modulation.
•   FM waves have varying frequency.
•   When there’s a trough in the signal, the frequency is increased, or on a peak it is increased. Or vice versa.
• Receivers recover the original signal.
• They ignore the carrier part of the wave and extract the original signal.
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## Note

Note :

The topics have only been summarised. Some key points may be missing :P apologies for this inconvenience. Please use your own resources in conjunction with these revision cards.

AND GOOD LUCK BHIRUNTHA!

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