refraction and diffraction of light, diagrams and explanations
Doc Brown's Physics Revision
Suitable for GCSE/IGCSE Physics/Science courses or
This page will answer many questions e.g.
How do draw ray diagrams?
What is refraction?
What is diffraction?
How do explain why waves refract or diffract?
Know and understand that light waves can be reflected,
refracted and diffracted.
Light waves are readily reflected off
smooth flat surfaces e.g. light reflected off a smooth surface like a mirror.
Know that light waves are
reflected and refracted at boundaries between different materials.
Apart from luminous objects
(give out their own light), we see objects by reflected light.
If the light is reflected from a
very smooth 'shiny' surface we see a mirror image eg a silvered mirror,
aluminium foil, shop window etc.
If the surface is uneven, the
light is scattered in all directions eg you don't see a mirror image looking
at tissue paper or a sliced section of apple.
a) Know that the normal is a construction
line perpendicular (at 90o) to the smooth reflecting surface at the point of incidence.
b) Know that the angle of incidence
is equal to the angle of reflection.
c) Know that the image produced in a plane
mirror is virtual, upright and laterally inverted.
You will be will be expected to
be able to construct ray diagrams to match these situations.
the vertical dotted line is the normal at
90o to the reflecting surface
reflection is the simple 'bouncing' off a plane
angle 2 = angle 3: angle of incidence i =
angle of reflection r
The construction of the ray diagram to show the
formation of a virtual image by a plane mirror and from which you can
deduce the characteristics of the virtual image.
The features of the virtual image formed by a
plane mirror are ...
The image is the same size as
The image is as far behind
the mirror as the object is in front of the mirror.
The image is upright -
the same way up as the object (if not it would be inverted, and you would
look upside down!).
The image is virtual
because the image appears to be behind the mirror.
The image is laterally inverted,
the 'left' of the object now appears on the 'right' side and the 'right' of
the object appears to be the 'left' side of the image.
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Diffraction is the effect
of waves spreading out when passing through a gap or passing by a barrier.
In effect, waves go round corners! and it doesn't matter if its sound, light
or water waves - they all diffract and bend round corners! The effect is so
small with light (tiny wavelength), you don't notice it, but you see water
waves bending around objects at the seaside and you can hear sounds from
round a corner.
You should appreciate that
significant diffraction only occurs when the wavelength of the wave is of
the same order of magnitude as the size of the gap or obstacle.
A: There is a relatively small
diffraction effect when waves pass through a wide gap that is much bigger
than the wavelength of the wave.
B: You get the maximum spreading
or diffraction when the light waves pass through a gap of similar size to the
wavelength of the incident waves.
You can see these effects with transverse
water waves at the seaside as waves hit the protective walls of a harbour
BUT you need a very tiny slit to observe diffraction with light waves
because of their tiny wavelength.
When you hold up a fine needle towards a
bright light, the edges aren't quite sharp because the light rays are
diffracting around the pin's surface.
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Waves - sound, light and astronomy revision notes index
introduction to the properties of waves, types of waves and their effects,
types, properties, uses and the spectrum of visible light
Sound waves - properties
explained, uses of sound including ultrasound
refraction and diffraction of visible light, diagrams and explanations
Optics - types of lenses (convex and concave), ray
The Structure of the Earth
, crust, mantle, core and earthquake waves (seismic waves)
The electromagnetic spectrum and astronomy -
solar system, cosmology, nuclear fusion and the life cycle of stars
The Big Bang Theory of the Universe, the
red-shift and microwave background radiation
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