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P13 Light - Coggle Diagram
P13 Light
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Snell's law
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Snell’s law gives the relationship between the angle of incidence i, and the angle of refraction r:
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The refractive index is related to the speed of light in the material (which is less than its speed in a vacuum):
refractive index, n = speed of light in vacuum ÷ speed of light in material
The refractive index is a number that is always bigger than 1 and is different for different materials
Refraction
When light enters a glass block, it slows down, causing it to change direction
When it leaves the block it speeds up again, changing direction once more
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Internal Reflection
When light is moving from a denser medium towards a less dense one, most of the light is refracted, but a small amount of it can be internally reflected
However, if the angle of the light is great enough then instead of being refracted, ALL of the light is reflected
This is called Total Internal reflection and happens when the angle of the incident ray is greater than the critical angle for that material
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Magnifying glasses
If the object is placed closer to the lens than the focal length, the emerging rays diverge and a real image is no longer formed
When viewed from the right-hand side of the lens, the emerging rays appear to come from a point on the left. This point can be found by extending the rays backwards (creating virtual rays)
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Reflection of light
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Angle of incidence, i = angle of reflection, r
Mirrors
When an object is placed in front of a mirror, an image of that object can be seen in the mirror
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Optical fibres
Total internal reflection is also used to reflect light along optical fibres, allowing the high-speed transmission of data on the internet
Additionally, optical fibres can be used in medicine in order to see within the human body
Converging lenses
When parallel rays of light (travelling parallel to the principal axis) pass through a lens, they are brought to a focus at a point known as the principal focus
The distance of the principal focus from the lens is called the focal length, and depends on how curved the lens is