The wave lengths for the light of red and blue colours

The wave lengths for the light of red and blue colours are nearly 7.8 x 10^-7 m and 4.8x 10^-7 m respectively.

1. Which colour has the greater speed in a vacuum?
2. Which colour has a greater speed in glass?

Answer

(i) In vacuum, both have the same speed.

(ii) In glass, red light has greater speed.