# Waves

• Created by: goliver3
• Created on: 11-01-17 09:28

## Progressive Waves

• Transverse waves are waves where the displacement of particles is perpendicular to the direction the wave is travelling in
• Longitudinal waves are waves where the displacement of particles in the same direction as the wave is travelling in
• Amplitude (A) is the maximum displacement of a particle in a wave from its equilibrium position (m)
• Frequency (f) is the number of complete waves passing a point in one second (Hz)
• Wavelength (lambda) is the distance between two identical points on a wave
• Wave speed (c) is measured in metres per second (ms^-1)
• c = f*lambda
• Points in a wave that are in phase travel in the same direction as eachother
• Points in a wave that are out of phase (antiphase) travel in the opposite direction to eachother
• If we measure distance travelled by two waves and then compare those distances, any difference in the distances travelled is called the path difference (m)
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## Longitudinal & Transverse Waves

• Mechanical waves occur in a medium e.g. solid, liquid or gas
• Longitudinal waves are waves where the displacement of the particles is in the same direction as the wave is travelling in e.g. sound waves
• Transverse waves are waves where the displacement of the particles is perpendicular to the direction the wave is travelling in e.g. water waves
• Electromagnetic waves are oscillating electric an magnetic fields they include radio waves, microwaves, infra-red, visible light, ultra-violet, x-rays and gamma rays
• Electromagnetic waves are transverse waves and they all travel at the speed of light in a vacuum
• Transverse waves can be polarised but longitudinal waves cannot
• Unpolarised light is a mixture if waves in different planes
• When unpolarised light is passed through a polaroid material/filter only light waves in one plane are transmited and the light is now polarised
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## Superposition

• The superposition of waves is when two waves pass through the same point they combine together to either constructively interfere with each other or destructively interfere with each other
• Constructive interference is when two waves are in phase with each other and constructively interfere to give a wave of greater amplitude
• Destructive interference is when two waves are out of phase (anti-phase) with each other and destructively interfere to give a wave of zero amplitude
• Stationary waves are formed by two waves with the same frequency, wavelength and similar amplitude travelling in opposite directions
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## Interference

• Laser light is a source of coherent monochromatic light
• Two waves are coherent if the phase difference between them is constant (same frequency)
• If a wave is monochromatic it means it only has one wavelength of light present
• When laser light passes through a slit it is diffracted, if there are two slits present the light will diffract at both slits
• If a screen is placed on the other side of the slits from the laser an interference pattern is seen, producing dark and light fringes
• w = fringe spacing (m)
• lambda = wavelength of the light (m)
• D = distance between the double slits and the screen (m)
• s = slit separation (m)
• w = (lambda*D)/s
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## Diffraction

• Diffraction happens when a wave hits an obstacle or gap, diffraction is greatest when the gap is about the same size as the wavelength of the wave, the waves bend round the object or spread out when they pass through the gap
• Single slit diffractionA diffraction grating is a piece of glass with lots of closely spaced parallel lines on it each of which allows light to pass through it, this is a transmission diffraction grating
• When monochromatic laser light is shone through a narrow single slit a diffraction pattern is produced consisting of light and dark fringes
• Wide central bright fringe
• Bright fringes getting dimmer as you move away from the centre
• Diffraction gratings are used in spectrometers, the diffraction grating splits up the light into a spectra
• d = grating spacing (m)
• theta = angle of diffraction
• n = order number
• lambda = wavelength on the light (m)
• lambda = dsintheta/n
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