# Light TRAVELLING/ANGLES OF INCIDENCESEECT

1. May 7, 2007

### strawberry7

1. Determine the time it takes for light to travel 54 cm through glycerine in an aquarium.
2. Red light travels from air into liquid at an angle of incidence of 390 and an angle of reflection of 170. Calculate the wavelength of the red light in the liquid if its wavelength in air is 750 nm.

I know a few formula's that may apply:
Ni * Sin(Ai) = Nr * Sin(Ar),

where:
Ni is the refractive index of the medium the light is leaving,
Ai is the incident angle between the light ray and the normal to the meduim to medium interface,
Nr is the refractive index of the medium the light is entering,
Ar is the refractive angle between the light ray and the normal to the meduim to mediuminterface

OR

sin-1 (nr/ni) = invsine (nr/ni)

But the problem is i think i am wrong. I can't find anything on wavelength for the second question. And am really confused. I know i don't have an attempted answer but that is because i have NO clue where to start. So i am not asking for an answer or anything, just a push in the right direcction of something, like which formula to use? or a website i can find information to help me with these questions..i am VERY lost

2. May 7, 2007

### Staff: Mentor

Some hints:
How fast does light travel through glycerine? (How does index of refraction relate to speed?)
Snell's law, which you quoted, should allow you to calculate the index of refraction of the liquid. (How does wavelength depend on speed and thus index of refraction as light goes from one medium to another?)

Last edited by a moderator: May 2, 2017
3. May 7, 2007

### strawberry7

The index of refraction for glycerine is 1.473, and the larger it is, the slower light travells. but i don't know which formula to use...

Once i found the index of refraction, which formula do i use that has wavelength?

4. May 8, 2007

### andrevdh

How does the speed of light in a medium relate to the refractive index of the medium?