Unit: Optics
Year: 1993 Question#: 87
Question: The diagram below shows light ray R parallel to the principal axis of a spherical concave (converging) mirror. Point F is the focal point of the mirror and C is the center of curvature.
After reflecting, the light ray will pass through point
(1 ) A
(2 ) F
(3 ) C
(4 ) D
What is this question really asking?
Explanation by: Danica A
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Answer 1
A
INCORRECT
The incident ray will not reflect straight back. It would have had to strike the mirror along a normal (perpendicular) line, which it does not. return to top
Answer 2
F
CORRECT
Light rays that run parallel to the principal axis are reflected through the focal point. Since ray R is running parallel to the principal axis, it will pass through point F, the focal point. return to top
Answer 3
C
INCORRECT
Point C is the center of curvature of the mirror. When ray R is reflected, it will pass through the focal point (see explanation for answer 2), not the center of curvature. return to top
Answer 4
D
INCORRECT
This point is on the mirror. Rays reflect off mirrors.
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What's this question really asking?
If a ray runs parallel to the principal axis, though which piont will the ray reflect?
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