Waves are the disturbances that are able to carry energy from one place to another. These waves can travel in both the denser as well as the rarer medium.
In the denser medium, the waves travel at a slower rate, and on the other hand, in rarer medium, the waves can travel at a comparatively faster rate.
As a wave moves from a layer of low velocity (denser medium such as a liquid) to a layer of high velocity (rarer medium like air), then the waves move away from the normal (perpendicular line) and result in the increase in the velocity of the wave.
I would suggest an easier route. So for example, I would research light energy, where it comes from, and what causes it. I won't be able to do the work for you though.
