AQA Physics A - Optics

Things you need to know about optics

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  • Created by: Tolu
  • Created on: 02-04-10 17:36
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Refraction of Light
Refraction is the change of direction that occurs when light passes non-normally across a boundary
between two transparent mediums. No refraction takes place if the incident ray is along the normal
At a boundary between two transparent substances, the light ray bends towards the normal if it
passes into a more refractive substance and away from the normal if it passes into a less refractive
substance.
The angle of refraction at P will always be less than the angle of incidence.
If i and r are the angles of incidence and refraction at point P then n = sini / sinr. If i and r are the
angles of incidence and refraction at point Q then 1/n = sini / sinr
NB* n means refractive index.
Young's Double Slit Experiment

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The first slit is used to help polarise the light from the lamp, it then goes through the double slits
which act as coherent sources of waves which emit light waves with a constant phase difference and
the same frequency. The interference is then shown on the screen producing alternate bright and
dark fringes that are equally spaced and parallel to the double slits.…read more

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Total internal reflection can only take place if the incident substance has a larger refractive index than
the other substance and if the angle of incidence exceeds the critical angle. The angle of refraction is
always 90° at the critical angle i.
A communications optical fibre allows pulses of light that at one end of a transmitter to reach a
receiver at the other end. Fibres are often transparent to reduce absorption. Cladding is put around
the fibre and has a lower refractive index.…read more

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Coherence
· Sources are coherent if they have the same frequency and a constant phase difference.
· Light from two nearby lamp bulbs can not from an interference pattern because the light
waves are emitted at random, meaning there is not a constant phase difference. Points of
cancellation and reinforcement change randomly so a pattern can not be formed.
Light sources
· Vapour lamps and discharge tubes, is a source of monochromatic light, because its spectrum
is dominated by light of one colour.…read more

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The central fringe is twice as wide as each of the outer fringes. And much brighter. The peak intensity
of each fringe decreases with distance from the centre The outer fringes all have the same width and
are much less intense than the central frige.
If different sources of monochromatic light is used then the greater the wavelength of the light, the
wider the fringes. The fringes can also become wider if the slit is made narrower.…read more

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The Diffraction Grating Equation
dsin = n
1. The number of slits per metre on the grating, N = 1/d
2. When given an order and wavelength the smaller teh value of d, the greater the angle of
diffraction.
3. Fractions of a degree are expressed either as a decimal or in minutes where 1° = 60'
4. To find the maximum number of orders produced, substitute sin as 1 and calculate n = d/ .
Round down to the nearest whole number.…read more

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Comments

Steroidsman123

Thank you! This is much better than the textbook and my teacher, I actually think I might learn this chapter from this :)

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