Waves

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  • Created by: bambi
  • Created on: 04-06-13 18:42

Nature of waves

A wave transports energy not matter

transverse wave 

a wave thats particles of the medium move perpendiculer to the direction which the wave moves

Examples are sea waves electromagnetic waves and waves on a string

Longitudal wave 

a longitudal wave is a wave in which the particles of the medium move parrallel to the direction the wave moves

examples of longitudal waves are sound and p waves 

polarised waves

polarised waves only travel in one direction, Passed through a grid (polaroid filter) , Creating waves in one plane .A polarising filter only allows light through which is in one direction ( remember its going in ONE DIRECTION). Polaristaion can only happen for transverse waves examples are tv aerials which polarise by the orintation of rods an the aerial . This is done to produce a strong signal. Other examples are 3d glasses and polarised sunglasses to reduce sun glare

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way to observe boundary behavior of waves

IN A RIPPLE TANK

A ripple tank is a large glass bottomed tank of water that is used to study the behavior of water waves 

light shines on the water from above and illuminates a white piece of paper placed directly blow the tank

A portion of light is aborbed by the water as it passes through the tank

a crest of water will aborb more light than the trough

. so the bright spots represent wave trough and the dark spots represent the wave crest

as waves encounter obsticles the the movement of the wave can be observed by watching the bright and dark spots on the sheet of paper

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In the ripple tank

Partitioned into a shallow and deep region . Pane of glass placed at the bottom of the tank one part of the tank will be deep the other part would be shallow . Waves travelling from the deep end to the shallow end will be seen to refract as the wavelengh decreases and the wave can be seen to slow down . when travelling from deep to shallow waterthe waves are seen to bend in a way that they seem toi be travelling more perpendicular to the surface . if the wave is travelling from shallow to deep water the waves bend in the opposite direction

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wave interference

constructive interference

occurs when waves are travelling in the same direction THere is upwards interference ina stationary wave this forms an antinode

deconstructive interference

2 interfering waves have a displacement in the opposite direction. The two waves cancel each other out . this forms a node( point of no interference) on a stationary wave

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refraction

when light passes from one medium to another it changes speed

this is because the speed of the wave is determined by the medium though which it is passing

to find out the refractive index you divide the speed of light by the speed of light in that substance

When light is travelling to a less dense material the speed on light in that material speeds up so the angle of refraction is bigger than the angle of incidence . The light refracts away from the normal exaples ase glass to water, water to air

When light is travelling into a more dense material the speed of light in that material slows down so the angle of refraction is smaller than the angle of incidence. the light refracts towards the normal 

The angle of refraction can not be greater than 90 degrees at the interface of two materials

When the angle of refraction is greater than 90 degrees the angle of incidence is called the critical angle.If any angle of incidence is greater than the critical angle total internal reflection occurs. the relationship between the critical angle and refractive index is sin=1/n

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diffraction grating

dsin =nlander for normal slits

n = wave order

sin = the angle from the zero order

d = the distance between the slits which may need to be worked out for example it is 300 slits per milllimetre ypu would do 1*10to the minis 3/300

lander= wavelength

IF THE QUESTION SAYS DOUBLE SLIT THE EQAUTION IS 

W=ladar D/s

W = fringe spacing

D= distance from the slits to the screen

s=the spacing between the slits (may need to divide wavelengh by number of slits) 

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diffraction grating

If the wavelengh of the wave is longer fringes more spaced out 

If the wave lengh is smaller the more narrow the fringes

white light produces bright white zero order, blue first order, red second order

red light red zero order blue first order

and so on

monochromatic means one wave lengh

coherent means constant phase difference

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