Physics Review Question Unit: Optics Year: 1992 Question#: 95 Question: The diagram below represents two rays of red light passing through a converging lens. if the two rays were blue light, f would be: (1 ) shorter (2 ) longer (3 ) the same What is this question really asking? Explanation by: Derek K [ Return to question menu ] Answer 1 shorter CORRECT Blue light has a shorter wavelength than red light and will therefore travel at a slower speed in the lens. This slower rate of travel will cause the blue light to be bend more than the red light, this will cause a decrease in focal length. This change in wavelengths can be nicely seen in a prism; also in prism the the shorter wavelengths can be seen to bend more dramatically. return to top Answer 2 longer INCORRECT Blue light has a shorter wave length than red light and will therefore travel at a slower speed in the lens. This slower rate of travel will cause the blue light to be bend more than the red light, this will cause a decrease in focal length. This change in wavelengths can be nicely seen in a prism; also in prism the the shorter wavelengths can be seen to bend more dramatically. return to top Answer 3 the same INCORRECT Blue light has a shorter wave length than red light and will therefore travel at a slower speed in the lens. This slower rate of travel will cause the blue light to be bend more than the red light, this will cause a decrease in focal length. This change in wavelengths can be nicely seen in a prism; also in prism the the shorter wavelengths can bee seen to bend more dramatically. A piece of test taking advice: you can be pretty sure that some change will occur so don't chose this answer. return to top Answer 4 only three possible answers to this question return to top What's this question really asking? This question is asking about differences in how light bends due to different wavelengths in a lens. Blue light has a shorter wave length than red light and will therefore travel at a slower speed in the lens. This slower rate of travel will cause the blue light to be bend more than the red light, this will cause a decrease in focal length. This difference in amount of bend can be nicely observed in a prism. return to top
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