AS Physics Unit 2: Waves Notes

These are not my notes i just put them in document form, they're from this website ->http://physicsnet.co.uk/

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  • Created on: 26-04-14 13:49
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Progressive Waves
Waves move energy from one place to another. In a progressive wave the wave front moves through the medium. There are two types of waves, transverse and
longitudinal.
Transverse waves are waves where the displacement of the particles in the medium is perpendicular to the direction the wave is travelling in.
Longitudinal waves are waves where the displacement of the particles in the the same direction as the wave is travelling in.
Describing waves
Amplitude (A) is the maximum displacement of a particle in a wave from its equilibrium position. It is measured in metres (m).
Frequency (f) is the number of complete waves passing a point in one second. It is measured in hertz (Hz).
Wavelength () is the distance between two identical points on a wave (i.e. one full wave). It is measured in metres (m).
Wave speed (c) is measured in metres per second (ms-1).
Wave speed (c), frequency (f) and wavelength () are linked together in the following equation.
c = wave speed (m s-1)
f = frequency (Hz)
= wavelength (m)

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Phase
Points on a wave which are always travelling in the same direction, rising a falling together, are in phase with each other.
Points on a wave which are always traveling in opposite directions to each other, one is rising while the other is falling, are in antiphase with each other.
Path difference
If we measure the distance travelled by two waves and then compare those distances, any difference in the distances travelled is called the path difference. Path
difference is measured in metres (m).…read more

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Longitudinal & Transverse Waves
Mechanical waves occur in a medium (solid, liquid or gas).
Longitudinal waves are waves where the displacement of the particles in the the same direction as the wave is travelling in. For example sound waves.
Transverse waves are waves where the displacement of the particles in the medium is perpendicular to the direction the wave is travelling in. For example water waves.…read more

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Refraction
Refractive Index (n)
The refractive index (n) of a material is the ratio of the speed of light (c) in a vacuum to the velocity of light in the material (cS).
The refractive index of a material is always greater than 1.
For example;
water = 1.33
diamond = 2.42
glass = 1.5
air 1
When a ray of light goes from material (1) into material (2), rather than from a vacuum into a material we talk about the relative refractive index.…read more

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Critical angle c
When a ray of light goes from a material into an optically less dense material like air. The angle of refraction can become 90o and the ray of light travels along the
boundary between the two material.…read more

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If the second material is air then n2 = 1 and so
If the incident angle is greater than the critical angle then light reflects at the boundary between the two material and this is called Total Internal Reflection.
Step index optical fibres
This is has a fine glass core and it is surrounded by a cladding of glass with a lower refractive index than the core.…read more

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The optical fibre would work without the cladding as air also has a lower refractive index than the core glass. However the cladding is useful as it protects the core,
prevents cross talk and prevents the leakage of light.…read more

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Stationary waves Stationary waves are formed by two waves with the same frequency travelling in opposite directions.
Interference
Laser light is a source of coherent monochromatic light.
Coherence - two waves are coherent if the phase difference between them is constant. For this to be the case they must have the same frequency.
Monochromatic - means having only one wavelength of light present.
Young's double slit experiment
When laser light passes through a slit it is diffracted.…read more

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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, this is called diffraction.
Single Slit Diffraction
When monochromatic laser light is shone through a narrow single slit a diffraction pattern is produced consisting of light and dark fringes. It produces a wide central
bright fringe.…read more

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This equation can be rearranged to
If there are N lines per metre on a diffraction grating then d can be calculated using
Diffraction gratings are used in the spectral analysis of light from stars.…read more

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