# P6 physics full

full P6 physics

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• Created by: callum
• Created on: 24-05-11 14:05

## What are waves.

A Wave is a disturbance that transfers energy in the direction of the wave.

A wave comes form a source that vibrates.

A transverse waves particles vibrate at right angles to the direction of the wave. Water waves are transverse.

A longitudal waves particles vibrate in the same direction as the wave. Sound waves are Longitudal.

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## Describing waves

Frequency is the number of waves the source makes every second.

Frequencys units are hertz Hz.

Wave speed ( m/s ) = frequency ( Hertz Hz ) X wavelength ( meters )

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## Reflection

When waves are Reflected the angle of incidence = the angles of reflection.

Mirrors reflect waves.

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## Refraction

The speed of a wave depends on its medium. If a wave travel through one medium to another , its speed changes.

When a waves speed changes its wavelength also changes, this is Refraction.

More speed change means more direction change.

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## Diffraction

When waves pass through a narrow gap they bend and spread out. This is Diffraction.

The gaps width must be similar to the waves wavelength.

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## Interference

when to waves of the same frequency meet, the effects of the waves add. This is Interference.

If two waves arrrive in step they reinforce. This is contructive Interference.

If two waves arrive out of step they cancel out. this is destructive Interference.

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## Evidence for lights wave nature

- light rays interfere. They could not do this as a stream of tiny particles.

- light rays can be diffracted.

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Electromagnetic waves consist of vibrating electric and magnetic fields.

Increasing Wavelength

<---------------------------------------------------------------------------------------

radio         microwaves  visible   ultraviolet  X-rays  gamma rays                waves                                light

---------------------------------------------------------------------------------------->

increasing frequency

All electromagnetic waves have these properties:

-They can travel through space.

- They travel through space at the same very fast speed.

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Electromagnetic waves emits energy which is absorbed or transmitted in 'packets' called Photons.

High frequency photons carry more energy than low frequency photons.

The amount of radiation of beam of Electromagnetic radiation delivers every second is its Intensity.

Intensity depends on:

- Amount of energy that each photon carries.

- The number of photons that arrive each second.

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Radio waves are used to carry info for radio and t.v programmes.  This is because they are not strongly absorbed by the atmospere.

microwaves can be used for heating food that contains water. This is because they are strongly absorbed by water molecules.

light and infrared radiation can be used for carrying info along optical fibers. This is because they lose only a little amount of energy when travelling through optical fibers.

X-rays can be used for taking shadow pictures of bones and luggage. This is because they are absorbed by dense materials but not as much by less dense ones.

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Radio, t.v and telephone signals can be carried by:

- radio waves and microwaves though space and the earths atmosphere.

- Light rays and infrared rays though optical fibers.

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## Analogue signals

Analogue signals can be used to carry info. They are made to vary in amplitude. The patter of variation carries the info.

The signal carries by AM and PM radio waves is an Analogue signal.

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## Digital signals

The info is transmitted Digitally.

Sound waves are converted into a digital code consisting of two values ( 0,1 ).

The digital code is transmitted as short waves called pulses.

Radio receivers decode the pulses to make a copy of the original sound.

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## Analogue vs Digital

As signals travel the pick up random unwanted electrical signals. this is called noise or interference

Analogue and digital signals decrease in intensity as there amplitude gets smaller. So radio receivers must amplify the signal they receive including noise and interference.

Digital produces signals with higher quality because:

- 0 and 1 can still be recognised even if noise has been added. So the signal can be cleaned up removing unwanted noise.

- However Analogue signals consist of many values and are amplified meaning noise cannot be removed.

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