Unit: optics
Year: 1991 Question#: 99
Question: The same frequency of monochromatic light is incident from air upon four lenses having the same curvature, but made of different materials. Which lens has the shortest focal length?
(1 ) (2 )
CROWN GLASS 
FLINT GLASS(3 ) (4 )
LUCITE 
FUSED QUARTZWhat is this question really asking?
Explanation by: SABA
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Answer 1
CROWN GLASS INCORRECT
The index of refraction for Crown Glass is 1.52. This material does not have the highest index of refraction out of all the materials given. Therefore, it will not bend the light the most to result in the shortest focal length.
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Answer 2
FLINT GLASSCORRECT
The index of refraction for Flint Glass is 1.61. This material has the highest index of refraction out of all the materials given, so therefore it will bend the light ray the most , resulting in the shortest focal length.
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Answer 3
LUCITEINCORRECT
The index of refraction for Lucite is 1.50. This material does not have the highest index of refraction out of all the materials given. Therefore, it will not bend the light the most to result in the shortest focal length.
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Answer 4
FUSED QUARTZINCORRECT
The index of refraction for Fused Quartz is 1.46. This material does not have the highest index of refraction out of all the materials given. Therefore, it will not bend the light the most to result in the shortest focal length.
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What's this question really asking?
To find the lens with the shortest focal length, the indexes of refraction of each material must be known to determine which will bend the light ray the most. So, the question is really asking which material has the highest index of refraction.
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