Question

Which color of white light travels fastest, in glass?
$(a)$ Red
$(b)$ Violet
$(c)$ Yellow
$(d)$ All of the above travels with same velocity

Answer 1

Hint: In this question use the concept that different colors of light have different wavelengths so the speed of light will too be different in different colors as the speed is dependent upon the wavelength of the color which is passing through a medium.

Complete step-by-step answer:
As we know that the velocity (v) of light is the product of frequency (f) and wavelength $\left( \lambda \right)$ of the light.
$ \Rightarrow v = f\lambda $...................... (1)

Now as we know that when the light travels in different medium frequency remains same but wavelength is different for different color of lights.

Now according to the concept that when the white light is passing through the prism it is scattered into seven different colors given as VIBGYOR.

Where, V = violet, I = indigo, G = green, B = blue, Y = yellow, O = orange, and R = red.
In these seven different colors the wavelength of light is in increasing order i.e. Violet light has minimum wavelength and red light has maximum wavelength.

So according to equation (1) velocity of light is directly proportional to the wavelength.
So violet color has minimum velocity of light and red color has maximum velocity of light when it passes through the glass.

Hence the red color of white light travels fastest in the glass.
Hence option (A) is the correct answer.

Note: A White light is composed of primarily seven main colors that is VIBGYOR namely violet, indigo, blue, green, yellow, orange, red. Red has the largest wavelength and the order of wavelength follows red>orange>yellow>green>blue>indigo>violet. Amongst these colors blue is the most scattered color and that’s why the color of the sky is blue.