Light waves are electromagnetic waves. This means that there does not need to be a medium for the wave to travel through and that it has a “universal” speed called the "speed of light." If you multiply the speed of light by the period, you get the distance the wave travels during one cycle. This is called the "wavelength." The electromagnetic spectrum given below describes the wavelength pictorially and numerically.
Note how small the visible light spectrum is relative to the entire spectrum. If you were to describe this to someone who did not know trigonometry, what would you say?

Question

Light waves are electromagnetic waves. This means that there does not need to be a medium for the wave to travel through and that it has a “universal” speed called the "speed of light." If you multiply the speed of light by the period, you get the distance the wave travels during one cycle. This is called the "wavelength." The electromagnetic spectrum given below describes the wavelength pictorially and numerically.
Note how small the visible light spectrum is relative to the entire spectrum. If you were to describe this to someone who did not know trigonometry, what would you say?

unklerhaukus · Answer

Light does not have a universal speed.
When light is travelling through a medium it will slow down.

openst · Answer

But how am I supposed to know that - without any knowledge of physics?

openst · Answer

It also says.. "Does something similar happen for sound waves?"

jim_thompson5910 · Answer

Sound waves need a medium to travel through. Which is why sound cannot travel in space.

openst · Answer

but how am I supposed to know this?
This is a pre calc question.. not a physics question.

jim_thompson5910 · Answer

I'm not sure. It sounds like your teacher is giving you homework that wasn't discussed during lecture (which is definitely unfair).

agent0smith · Answer

@UnkleRhaukus I think it still travels at the speed of light in a medium, it's just that the absorption and re-emission inside the material slow it's progress through it. I think the actual speed of light in the material is still just c.

agent0smith · Answer

https://www.physicsforums.com/threads/why-does-light-slow-down-in-a-medium.613481/

mrnood · Answer

Can't really see what this has to do with trigonometry either.

Also
@agent0smith 
It is not 'unfair' top be asked to find out stuff for yourself - it's called research - or learning.
Not everything you need to know will be spoon-fed to you by a teacher - the fun of learning is that it opens opportunities to learn more

agent0smith · Answer

er, what?

imqwerty · Answer

Mybe you just have to explain the dispersion of light using snell's law

zzr0ck3r · Answer

the only thing you used from trig is the word 'period' which can easily be explained. 

So explain it the exact same way.

mrnood · Answer

@agent0smith

sorry - my comment was meant to be  directed at @jim_thompson5910

unklerhaukus · Answer

the velocity of light is
    v = nc
where n is the refractive index of the medium 

@agent0smith

agent0smith · Answer

@UnkleRhaukus I know, but what I'm saying is the actual photons of light do not show down. The group velocity does. My explanation isn't correct about absorption and re-emission, but in the link there's more correct explanations.