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 [ Return to question menu ] 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. return to top 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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