What is white light? Why do we perceive different colors with a prism?

Question

Not a homework question.

Answer 1

I'll answer your 2 questions in the opposite order:

"Why do we perceive different colors with a prism?"

The back of the eye has tons of cells called rods and cones. These cells each detect one color of light, Red, Green, and Blue. We perceive purple when red and blue cones/rods are activated at the same time, and we perceive white light when all 3 colors are activated. This is because:

"What is white light"?

White light is composed of all the colors of the visible light spectrum. So when white light passes through the prism the prism alters the angle of the different colors of light.

Answer 2

White light is the sum of all wave lengths, when white light crosses a prism it separates in  different wave lengths each corresponding to a different color.

Answer 3

White light is the combination of all the wavelengths of the visible spectrum. A prism scatters light into all of its wavelengths, red has the longest wavelength and violet has the shortest.