Which of the following statements is correct regarding the propagation of light of different colours of white light in air?

(a) Red light moves fastest

(b) Blue light moves faster than green light

(c) All the colours of the white light move with the same speed

(d) Yellow light moves with the mean speed as that of the red and the violet light



  • The speed of light in air and vacuum is a constant (c=3 x 10 8 )
  • The speed of light only changes when it undergoes refraction. - it results in dispersion of light. 
  • Air is an optically rarer medium with the refractive index approx. 1.
  • Air does not result in any changes in the speed of light.  

changes in speed of lightleading to Dispersion-01.jpg

So, the correct answer is (c)

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo