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What are Ray Diagrams?
Ray diagrams
for a convex lens and a concave
lens are different
but to draw any ray diagram
you only need to know two things.
1. A ray passing
through the centre of a lens
will go straight through.
2. A ray parallel to
the principle axis of a lens
will go through the focal
point.
What is the Principle Axis and the Focal
Point of a Convex Lens?
The principle axis
is a horizontal line going through the
centre
of a lens
(shown as the normal on the previous
page).
Any light
ray parallel to
the principle axis will be refracted,
change direction and cross
the principle axis at the focal
point.
What is the Focal Length
of a Convex Lens?
The distance from the focal
point to the centre of
the lens
is called the focal length.
Almost parallel
rays of light come
from any object
that is
a long way (more
than 5 metres) from the lens
(continued).
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