Question

The wavelength of red light is ______ times greater than that of blue light.

A) 1.8

B) 18

C) 0.18

D) $\dfrac{1}{8}$

Answer 1

Hint: To solve this question first we need to know the wavelength for the red light and blue light then we will find the ratio of their wavelengths and in final we can conclude the wavelength of red light how many times of the wavelength of blue light.

Complete answer:

The visible light consists of seven colours. The wavelength of the visible light is in the range of 340 nanometre to 740 nanometres.

The visible white beam of light is made up of seven colours. These seven colours of the light get separated after passing through the prism. This phenomenon is known as the dispersion of light.

The wavelength of red light is 700 nanometres

The wavelength of blue light is 400 nanometres

Given:

Wavelength of red light, ${{\lambda }_{r}}=700\ \text{nm}$

Wavelength of blue light, ${{\lambda }_{b}}=400\ \text{nm}$

Taking ratio of both the wavelengths:

$ \Rightarrow \dfrac{{{\lambda }_{r}}}{{{\lambda }_{b}}}=\dfrac{700}{400} $ 

$ \Rightarrow \dfrac{{{\lambda }_{r}}}{{{\lambda }_{b}}}=1.75 $

$ \Rightarrow \dfrac{{{\lambda }_{r}}}{{{\lambda }_{b}}}\approx 1.8 $

The wavelength of red light is 1.8 times greater than that of blue light.

Hence, Option (A) is correct.

Note: The red colour in the visible range has maximum wavelength. The violet colour of the light has minimum wavelength. The visible light wavelength varies from violet to red colour.