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Wave theory (Refraction (Refraction through a prism (The amount light…
Wave theory
Refraction
Refraction: when light travels from air into glass, it slows down. It speeds up again as it leaves glass and re-enters air. This change in speed causes the light ray to bend.
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HOWEVER: If the light ray is travelling at 90 degrees to the boundary, it will not refract and just goes straight through.
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Refractive Index
Definition: a ratio of the sin(incidence angle) to the sin(refracted angle) when light moves across a boundary.
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Lenses
Converging (convex)
Parallel rays are focused onto one point (focal point F). The distance to this point is called the focal length (f).
During refraction, the rays in a convex lens converge.
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Diverging (concave)
Parallel rays are spread out; they appear to have come from one point. Since they haven't the rays on the left of the lens are virtual (dotted line).
During refraction, they rays in a concave lens diverge.
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In refraction, when parallel light rays bend towards the normal when they enter a denser medium and away from the normal when they enter a less dense medium.
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Waves
Longitudinal
Longitudinal waves make particles oscillate in a direction parallel to the direction of energy transfer.
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Transverse
Transverse waves make particles oscillate in a direction perpendicular (at 90 degrees) to the direction of energy transfer.
Example: water waves, waves on a string and electromagnetic waves.
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How to describe waves?
Wavelength: the distance between any two identical points on a wave (the length of one full cycle). Normally measured in metres. (long wavelength = loud; short wavelength = low)
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Frequency: this is the number of complete waves which pass a point in 1 second. Measured in Hertz (Hz) which means 'per second'. (high frequency = high pitch; low frequency = low pitch)
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Sound waves
Caused by vibrations. These vibrations squash and stretch the air immediately next to it, and then they bump into their neighbours and so on.
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Humans range: 20Hz - 20,000Hz
Electromagnetic spectrum
Speed: they all travel at the speed of light (300,000,000 m/s).
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Reflection
The law of reflection: the angle of incidence (the angle between the normal and the incident ray) must be the same as the angle of reflection (the angle between the normal and the reflected ray) on the other side.
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