Isaac newton used a to break white light into its component colors.

In the eighteenth century Isaac Newton found out that when a beam of light from the Sun, passes trhough a prism is decomposed in many different colors. He named this phenomenom as dispersion of light.

This phenomenom occurs when a beam of white light (which is compound of many wavelengths or "colors") is refracted (the different rays of light are diverted depending on their wavelengths) in some medium, leaving their constituent colors separated.  

Therefore:

gets less

at positions a, g kinetic energy is maximum.

at position d, potential energy is maximum.