Light · revision map · IGCSE 0625, Topic 3.2
TOPIC 3.2 · LIGHT
CAMBRIDGE IGCSE PHYSICS 0625 · ONE-PAGE REVISION MAP
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LIGHT3.2
Reflection
At a plane mirror the angle of incidence equals the angle of reflection.
angle of incidence = angle of reflection- The image is virtual, upright, the same size.
- As far behind the mirror as the object is in front, and laterally inverted.
Refraction
Light bends when its speed changes at a boundary.
- Entering a denser medium it slows and bends toward the normal; leaving, it bends away.
- The frequency stays the same; speed and wavelength change.
Dispersion of White Light
A prism splits white light into a spectrum; each colour refracts by a different amount.
- Red bends least, violet bends most.
- Order: red, orange, yellow, green, blue, violet.
Refractive IndexEXTENDED
The refractive index n measures how much a medium slows and bends light.
n = sin i / sin r
n = refractive index, i = angle of incidence, r = angle of refraction
n = 1 / sin c
n = c / v
in n = 1/sin c, c = the critical angle; in n = c/v, c = speed of light in a vacuum and v = its speed in the medium. Both relationships are Extended.
Thin Lenses
A converging (convex) lens bends parallel rays to a principal focus F. Focal length f = lens to F.
- An object beyond 2F gives a smaller, inverted, real image.
- Inside F the lens acts as a magnifying glass (a larger, upright, virtual image).
Total Internal ReflectionEXTENDED
Inside a denser medium, if the angle of incidence exceeds the critical angle c, all the light reflects.
- Needs light going from dense to less dense; linked by n = 1 / sin c.
- Optical fibres carry telephone, internet and endoscope signals with little loss.