Physics Review Question

Unit: optics
Year: 1996 Question#: 95
Question: The focal length of a lens is NOT dependent on the
(1 ) material from which the lens is made
(2 ) color of the light incident on the lens
(3 ) distance of an object from the lens
(4 ) shape or curvature of the lens

What is this question really asking?

Explanation by: Chuck Hoke

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Answer 1
material from which the lens is made

Incorrect. The focal length does depend on the material from which the lens is made. Materials with higher indices of refraction refract light more and thus have shorter focal lengths.
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Answer 2
color of the light incident on the lens

Incorrect. The focal length does depend on the color of the light incident on the lens. The shorter the light's wavelength, the greater the refraction (this principle is known as dispersion). Thus lenses have shorter focal lengths for short wavelengths. return to top



Answer 3
distance of an object from the lens

Correct. The focal length is a property of the lens. The object distance affects the image distance only. return to top

Answer 4
shape or curvature of the lens

Incorrect. The focal length does depend on the shape or curvature of the lens. Greater curvature shortens the focal length. return to top


What's this question really asking?

What does the focal length of a lens depend on? return to top

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