When a beam of white light passes through a glass prism, the colour of light beam that deviates the least is
- A.Blue
- B.Red
- C.Green
- D.Violet
Correct answer
Explanation
The correct answer is B, Red. Red light has the longest wavelength in the visible spectrum, so glass slows it the least and bends it the least.
A prism splits white light into seven colours, VIBGYOR, because the refractive index of glass is slightly different for each wavelength. This splitting is called dispersion and was first explained by Isaac Newton. Red light, with a wavelength of about 700 nm, travels fastest in glass and is deviated least, so it appears at the top of the spectrum. Violet, at about 400 nm, travels slowest and is deviated most. The same effect, with raindrops acting as prisms, forms a rainbow.
A is wrong because blue light bends more than red, as its wavelength is shorter. C is wrong because green lies in the middle of the spectrum and is deviated more than red. D is wrong because violet is deviated the most, not the least.
Exam tip: red least deviated, violet most; longer wavelength means less bending.
Practice Questions
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- B.nose
- C.ear
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