Quick Answers:

1) The single beam of light would now comprise of all the colours of the visible spectrum. This will result in white light being observed

2) White light is made up of all the colours of light that form the visible spectrum. Each colour has a specific frequency.

When white light enters a different medium (ie Perspex) the frequency of each colour remains constant but the speed of each colour will change.

The degree to which each colour refracts depends on the speed of the light in the medium. As each colour travels at a different speed in the new medium, each colour will refract a different amount.

Red light refracts the least through to violet which refracts the most