# PHYSICS UNIT 2: OPTICS

Information on all types of diffraction, with images, and further information. some is borrowed from another user, but i added further detail- GOOD LUCK :))

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OPTICS
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 (if it
slows down) and away from the normal if it passes into a less refractive
substance (if it speeds up).
· n sin i = n sin r
Young's Double Slits
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
· If the single slit is too wide then the dark fringes become narrower than
the bright fringes and contrast between the two is lost
· Where bright fringes are formed, the light from one slit reinforces the
light from the other slit, meaning they are in phase with each other
Here dark fringes are formed the light from one slit cancels light from the
other, meaning they arrive 180° out of phase
· w=D/s
· The fringes become more widely spaced if the D is increased, the
wavelength is increased or the slit spacing is reduced
· NB* w is fringe separation, is wavelength, D is distance from the slits to
the screen, and s is the slit spacing
Total Internal Reflection
· 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
· Total internal reflection occurs at the core-cladding
· The core must be very narrow to prevent multipath dispersion
· Light used should also be monochromatic.
· sin = n / n

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Diffraction
· The central fringe is twice as wide as each of the outer fringe & 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 fringe
· The fringes become wider if the slit is made narrower
· W =2D/a
· The width of each fringe is proportional to /a
NB* a is the width of a single slit, W is the…read more

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