When a light beam falls on a triangular glass prism, a band of colours is obtained. Which one of the following statements is correct in this regard?
- A.Red light bends the most, as the refractive index of glass for red light is greatest.
- B.Red light bends the most, as the refractive index of glass for red light is lowest.
- C.Violet light bends the most, as the refractive index of glass for violet light is greatest.
- D.Violet light bends the most, as the refractive index of glass for violet light is lowest.
Correct answer
Explanation
The correct answer is C, Violet light bends the most, as the refractive index of glass for violet light is greatest. The more a colour is slowed by glass, the higher the refractive index for it and the more it bends.
When white light enters a prism, each colour is refracted by a different amount because the refractive index of glass depends on wavelength. Violet, with the shortest visible wavelength, faces the highest refractive index and is deviated the most; red, with the longest wavelength, faces the lowest and is deviated the least. The colours therefore fan out into the spectrum VIBGYOR. Isaac Newton showed that a second, inverted prism could recombine the colours into white light, proving that white light is a mixture of colours.
A is wrong: red bends the least, and the refractive index of glass is lowest for red, not greatest. B is wrong: the lowest refractive index for red makes it bend the least, not the most. D is wrong: violet does bend the most, but because its refractive index is the greatest, not the lowest.
Exam tip: in dispersion, violet has the highest refractive index and deviation, red the lowest; the order of colours is VIBGYOR.
Practice Questions
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- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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- D.Eyepiece-Objective lens-Body tube-Mirror
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- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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