Unit: Optics
Year: 1991 Question#: 93
Question: A light ray is incident upon a cylindrical reflecting surface as shown in the diagram at the right. The ray will most likely be reflected toward letter
(1 ) A
(2 ) B
(3 ) C
(4 ) D
What is this question really asking?
Explanation by: Steven B
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Answer 1
A
INCORRECT
This is incorrect because the reflected ray will always be on the opposite side of the normal as the incident ray is. return to top
Answer 2
B
INCORRECT
This is incorrect because rays will always reflect away from the normal, and ray B goes along the normal. return to top
Answer 3
C
CORRECT
C is correct because a ray bounces off of a surface at an angle away from the normal equal to that of the incident ray, but on the opposite side of the normal. The normal to the surface of the cylinder can be found by imagining a line tangent to the cylinder where the light strikes the cylinder. The normal is the line perpendicular to this tangent line.
return to top Answer 4
D
INCORRECT
D is incorrect because ray D's angle from the normal is greater than that of the incident ray. return to top
What's this question really asking?
The question is really asking how to find the normal to a curved surface because you have to know the normal to figure out how the incident ray will reflect. return to top
