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Light - Total Internal Reflection - Prisms.
A right angle prism can be
used to change the direction
of a light ray
by 90 degrees or 180 degrees
(a prism can also be used to disperse
white light into a spectrum).
A right angle prism
is used to change the direction
of light by 90 degrees
as shown below.
The light ray enters
along a normal
and continues straight on until it hits
the back face of the prism.
Total internal reflection
occurs here
because light strikes the surface
at 45 degrees
which is greater than the critical
angle.
The light ray then emerges
from the prism along a normal
and so continues straight through.
This type of prism can be used in a periscope.
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