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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
Transverse waves are waves where the displacement of the particles in the medium is perpendicular to the direction the wave…

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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…

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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…

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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 =…

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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. When this happens the angle of incidence is called the…

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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…

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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.
The core should be narrow as this cuts down on multi-mode…

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Stationary waves Stationary waves are formed by two waves with the same frequency travelling in opposite directions.

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…

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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…

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d = grating spacing in metres (m)
= angle of diffraction
n = order number
= wavelength on the light in metres (m)
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…


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