Question

Which colour of light travels fastest in any medium except air?
A. Red
B. Violet
C. Blue
D. Orange

Answer 1

Hint: When a light of only one color(monochromatic light) is passed into prism that light suffers deviation. We can relate that prism as a sudden medium changing instrument in the dispersion case. But when white light is passed the case is different. All this is due to change of medium which causes change in refractive index. We will answer this question by using these hints.
Formula used:
$v = \dfrac{c}{n}$

Complete answer:
When white light is passed through any transparent material let us assume prism the light gets separated into its individual component colors and gets out of that prism. This process of separation of light into its individual components is called dispersion of light
normally those colors are called as VIBGYOR where
VIOLET(V)
INDIGO(I)
BLUE(B)
GREEN(G)
YELLOW(Y)
ORANGE(O)
RED(R)
Each color has its own wavelength where violet has the shortest wavelength while red has the longest wavelength
Refractive index of each individual light varies with its wavelength and frequency. For higher frequency refractive index will be more and that color deviates more and lower frequency rays have less refractive index and deviates less.

Since violet has less wavelength and higher frequency it deviates more while red has higher wavelength and less frequency hence deviates less.
Velocity of light will be different in different media. If velocity of light is higher in one medium and lesser in another medium then the first one is called a rarer medium and the second one is called denser medium.
Velocity of light is dependent on refractive index as $v = \dfrac{c}{n}$
Where ‘n’ is the refractive index and ‘c’ is the velocity of light. As the refractive index of red color is less as described above, the velocity of red light will be more in any medium except air.

Hence option A is the answer.

Note:
It is to be remembered that prism slows down violet light a lot and hence it will be travelling a longer path than red light inside prism. In the process of formation of rainbow raindrops act as prisms and cause dispersion of the sunlight. Scattering of light in fog is also due to dispersion of light by fog .