The reflection and refraction of waves
The reflection and refraction of waves at a series of different boundaries are shown in the
following diagrams. (For the present diffraction effects have been ignored.)
Plane wave
Circular wave
Plane wave reflection from
a flat barrier
Plane wave reflection from
a convex barrier
Circular wave reflection from a
flat barrier
Circular wave reflection
from a concave barrier
shallow
deep
Plane wave refraction
Plane waves and a
sloping beach
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Prism
Convex lens
Concave lens
Figure 4
One of the most important diagrams is that showing that when waves pass from deep to
shallow water, or when light passes from an optically less dense to an optically more dense
material, there is refraction and also a change of wavelength. This is due to a change of
wave velocity - the velocity in the more dense medium being less than that in the less dense
medium. A full proof is given in the discussion of Huygens’ wave theory, but the results will
be summarised here as follows:
When a light wave passes from a less dense to a more dense material:
(a) there is a decrease in wave velocity,
(b) there is a decrease in wavelength,
(c) the frequency of the wave remains constant, and
(d) the ratio of the velocities in the two media is equal to that of the two wavelengths.
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