Question

The wavelengths for the light of red and blue colors are nearly $7.8\times {10}^{-7}m$ and $4.8\times {10}^{-7}m$ respectively.

(a) Which color has the greater speed in a vacuum?

(b) Which color has the greater speed in glass?

Answer 1

(a) In a vacuum, both red and blue lights travel at the same speed. Since in the vacuum, there is no medium so light of both cols will travel with the same speed that is with the speed of light.

(b)When red and blue light are traveling in glass their speed will depend on the refractive index of the glass.

It is $v=\mu \lambda$ where $\mu$ is the refractive index

from the above equation we can say that since the wavelength of the red light is more so it will travel with more speed in the glass