AQA A Physics AS - Chapter 13 Optics Revision Notes


These are the notes for AS Physics AQA A specification chapter 13 - optics

you can use them with my chapter 12 - waves notes (they have also been uploaded)

hope you find them useful...

i'm sorry if i've made any mistakes (please feel free to correct me! :D)

good luck :)

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  • Created by: ADB :)
  • Created on: 31-03-11 11:21

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Page 1

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Refraction of Light

The wave theory of light can be used to explain reflection and refraction of light. However,
when we consider the effect of lenses or mirrors on the path of light, we usually prefer to
draw diagrams using light rays. Light rays represent the direction…

Page 2

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sini = constant = refractive index of substance (n)

remains constant for all values of (i) and (r) - This is Snell's Law.
We call the constant from Snell's law the refractive index (n)
The refractive index always has a value greater than 1 (Refractive index of air is…

Page 3

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sini c1
sinr = c2

Can be rearranged to give
c1 sini = c12 sinr

Multiplying both sides of this equation by (c)
c c
c1 sini = c2 sinr

Substituting n1 for c1
where n1 is the refractive index of substance 1
And n2 for c2…

Page 4

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The glass prism refracts light by different amounts, depending on its wavelength.
The shorter the wavelength in air, the greater the amount of diffraction.

Total Internal Reflection

Remember: Partial
Internal Reflection always occurs at a boundary when the angle
of incidence is less than or equal to the critical angle.…

Page 5

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OPTICAL FIBRE is a thin flexible transparent fibre used to carry light pulses from one end
to the other.

Communications Optical Fibre:
A communications optical fibre allows pulses of light that enter at end, from a
transmitter, to reach a receiver at the other end. Such fibres need to be…

Page 6

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Spectral Dispersion: The speed of light in glass depends on its wavelength.
Therefore, if white light is used, violet light travels more slowly than red light. The
difference in speed would cause white light pulses to become longer and merge
into each other.
Spectral Dispersion is prevented by using a…

Page 7

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Double Slit Interference

The single slit causes diffraction of the light so that the same wavefront illuminates both of
the double slits. Therefore, the double slits act as coherent sources because the light
emerging from them is from the same wavefront.

Diffraction at the double slits causes the two sets…

Page 8

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Constructive Interference: occurs when the path difference is zero or a whole number of
wavelengths so that the signals arrive in phase. (At a bright fringe)

P ath Difference = n

Destructive Interference: occurs when the path difference is an odd number or half
wavelengths. (At a dark fringe)


Page 9

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At the first fringe either side of the pattern, the path difference is
one wavelength. For the second fringe either side of the pattern,
the path difference is two wavelengths, etc.

To measure the fringe separation (w) measure across several fringes from the centre of a dark fringe to the…

Page 10

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Laser is a convenient source of COHERENT light: When used during the double
slits investigation, we can illuminate both slits directly using the laser. Unlike
non-laser sources where we have to pass it through a narrow single slit first.

White Light Fringes
White light has all the wavelengths present in…


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