# Homework Help: Refraction of light-apparent speed

1. Nov 20, 2007

### irunwithmonkeys

1. The problem statement, all variables and given/known data
Imagine two media: one is thick air and the other is a liquid medium of some kind. The index of refraction of the air medium is 1.2
and that of the liquid medium is 1.47.
You are standing in the air medium looking straight into the liquid medium. You observe an object inside the liquid medium moving directly towards you. The speed of the object is 20 m/s. Assume the glass wall is very thin and that it doesn't affect the results. What is the apparent speed of the object as seen by you?

2. Relevant equations

I used c = v/n so v = c/n

3. The attempt at a solution

v=c/n= 20 [m/s] divided by 1.47 = 13.6 [m/s]

Can someone please help verify this is correct. Or am I doing this all wrong? Thank you very much for helping. I really appreciate it.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 21, 2007

### rl.bhat

v=c/n= 20 [m/s] divided by 1.47 = 13.6 [m/s] In this formula v is the velocity of the light in the medium, not the object. If T and T' are the real and apparent depths in the liquid then you can wright 1.47/T = 1.2/T'. After 1 second real depth becomes T - 20 m and apparent depth will be T' - X. Find X