# WAVES -Notes and Revsion

Quick note about the waves and different propeties

Not in order....

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## Wave Properties 2

Dispersion- When White light enters a prism, the colours are split depending of the wavelength

Total Internal Reflection - All the light remains in a medium and is reflected back- angle > critical angle = reflection - light doesn't pass the boundary

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## Equations

Intensity is proportinal to amplitude^2

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## Waves - Mechnical and Electrical

Waves transfer energy without transferrring matter

The energy is transferred by ocillations vibration

MECHANICAL WAVES:Waves that travel trough a material

ELECTRONIC WAVES:Waves that are trasferred by electrical and Magnetic fields- no material needed

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## Polarisation of Waves

WHAT ARE POLARISED WAVES?

Vibration of the waves only occur in ONE plane perpendicular to the direction of the wave/

*Longitudinal waves can't be polarised because the particles are parallel to the energy transfer

How do 3D glasses work?

• Screen is polarised
• Left lenses and right lenses are 90 degrees to each other (perpendicular plane)
• Both eyes recieve different images, giving the pictures depth.
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## Waves - Longitudinal and Transverse

LONGITUDIAL WAVES:Oscillations Occure parallel to th direction of travel- eg. Sound waves , Ultra-Sound waves

|||||| | | | | | ||||| | | | | |||||| | | |||||| ||| | | | | | |||||||| --> Direction of travel

E                     C

E- expansions (Rarefraction)         C- compressions

Transverse waves

Oscillations Occur at right angles perpendicular to the direction of travel- eg, EM waves, waves on a String /Wire

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## Wave Properties

Reflection - Waves will bounce off a surface under certain conditions-e.g shiny surfaces for EM waves

Refraction - Waves cross a boundary causing a change in speed and wavelength- this depends oon the refractive index of different substances

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## Diffraction

Depending on the gap and the wavelength of the wave, will affect the effect of diffraction on the wave.

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## Equations + fibre Optics

Fibre Optics - Used in communication- critical angle has to be low to allow as much as light as possible to be internally reflected, this means that the refractuve index has to be high

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## Phase Difference

Phase Difference- Phase difference means waves have the same frequency but different oscillations to each other.

'IN PHASE'-same frequency, same peaks, different amplitudes

'ANTI-PHASE' - waves start opposite to each other; e.g 1st wave is (x) behind the 2nd wave

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## Polarisation of Waves 2

FILTER 1)WHY?

• When the permitted direction of vibration or polarisation of the filter is parallel to the direction of the polarisation of the wave, it is transmitted by the filter.

FILTER 2) WHY?

• When the permitted direction if vibration or polarisation of the filter is perpendicular to the direction to the direction of the wave, it is absorbed or reflected back, but not transmitted
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## Coherence and Superposition

Coherence - The two waves are said to be 'coherent' if they have the same frequency and the same constant phase difference

Superposition - When 2 waves meet they will interfere and superimposed (sat on top of)

The principle of superposition may be applied to waves whenever two (or more) waves travelling through the same medium at the same time. The waves pass through each other without being disturbed. The net displacement of the medium at any point in space or time, is simply the sum of the individual wave displacements.

At any point they meet, trhe two waves will combine to give a resultant wave whose amplitude (intensity) may be greater or less than the original two waves.

The resultant displacement can be formed by adding the two displacements togther

THIS IS CALLED THE PRINCIPLE OF SUPERPOSITION

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## Waves and Interference

Constructive Interference- when 2 crests/troughs of two waves coincide, they combine to create an amplified wave, the 2 waves are inphase with each other  - there is ZERO phase diffrence between them.

Destructive Interference - When crests of 1 wave are aligned with the trough of another, they cancel each other out. The waves are out of phase (anti-phase) with each other - they are 1/2 a cycle different from eachother.

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## Waves

Definitions:

Displacement The distance from the equilibrium position

Wavelength The distance between 2 idetnical points on a wave train

Amplitude Maximun Dispalcement of a particle

Frequency Amount of Complete waves passing a point in 1 second

Period The time taken for 1 wave to pass a point

Peak/Trough Highest and lowest point in a wave

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## Diffraction and Interference

Path Difference - Difference in distance between 2 sources and the screen

Interference from 2 sources

• Two sources much be in phase and coherent
• Constructive or  destructuve inteference depends on path difference
• Path difference is the distance the wave from 1 wave travel more than the wave of the other source.
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## Standing waves

Progressive Wave

• Transmits energy and transform shape

Standing/ Stationary Wave

• Stores Energy (stays in the same place) and shape is consistent (doesn't change)

Foward wave interferes with the reflected wave--> this creates constructive and destructive inteference with max +ve and max -ve amplitudes--> also creates destructive interference with 0 amplitude. SOURCES ARE COHERENT

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