Finding the image made by a lens by a scale diagram
The image can be found
by a diagram as shown below.
The object and focal length are drawn to scale and then
three rays are drawn from the object:
(a) the axis;
(b) a ray from the top of the object
parallel to the axis (A);
(c) a ray from the top of the object passing through the
centre of the lens (B).
Where rays (b) and (c) cross is the top of the image.Two examples of this are shown below.
Convex lens with the object further from the lens than its focal length
After
passing through the lens ray A will go through the principal focus
(F).
Convex lens with the object closer to the lens than its focal length
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