Time it takes for light to travel 54 cm

  • #1

Homework Statement



How do you find the time it takes for light to travel 54 cm through glycerin (index of refraction = 1.470 at 20˚C) in an aquarium?

Homework Equations



These equations might be useful: v= 331 m/s + (0.59 m/s/c˚)(T) niSinθi=nRSinθR

The Attempt at a Solution



v= 331 m/s + (0.59 m/s/c˚)(20˚C)
v= 331 m/s + 11.8 m/s
v= 342.8 m/s

Δt= 0.54 m ÷ 342.8 m/s = 0.0015752 s

But this isn't the right answer
 
Last edited:

Answers and Replies

  • #2
HallsofIvy
Science Advisor
Homework Helper
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Your problem says "1.470 at 20˚C" which I would interpret to mean that the speed of light in glycerin, at 20˚C, is 1.470 times the speed in vacuum- which would mean that, since you problem asks about the time at 20 C˚, there would be NO correction for temperature.
That is, the speed of light in glycerine, at 20˚C is just the speed of light in vacuum times 1.47.

If I am misinterpreting that, then what is the "0" point for T? 0˚Celcius or (more common) 0˚Kelvin?
 
  • #3
1. Homework Statement

How do you find the time it takes for light to travel 54 cm through glycerin (index of refraction = 1.470 at 20˚C) in an aquarium?

2. Homework Equations

These equations might be useful: v= 331 m/s + (0.59 m/s/c˚)(T) niSinθi=nRSinθR

3. The Attempt at a Solution

v= 331 m/s + (0.59 m/s/c˚)(20˚C)
v= 331 m/s + 11.8 m/s
v= 342.8 m/s

Δt= 0.54 m ÷ 342.8 m/s = 0.0015752 s

But this isn't the right answer
 
  • #4
1,137
0
is the answer : 2.626 x 10^-9 ???
 
  • #6
1,137
0
well i didnt use your first eqn

i used: refractive index = (velocity of light in vaccum = 3 x 10^8) / (velocity of light in vaccum)

find velocity in glycerin and use d=vt
 
  • #7
ehild
Homework Helper
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1,909
[
These equations might be useful: v= 331 m/s + (0.59 m/s/c˚)(T)
That formula might refer to the speed of sound in air.

ehild
 
  • #8
berkeman
Mentor
58,774
8,903
is the answer : 2.626 x 10^-9 ???
Please do not give answers to homework questions. That is against the PF Rules (see the link at the top of the page).
 
  • #9
berkeman
Mentor
58,774
8,903
1. Homework Statement

How do you find the time it takes for light to travel 54 cm through glycerin (index of refraction = 1.470 at 20˚C) in an aquarium?

2. Homework Equations

These equations might be useful: v= 331 m/s + (0.59 m/s/c˚)(T) niSinθi=nRSinθR

3. The Attempt at a Solution

v= 331 m/s + (0.59 m/s/c˚)(20˚C)
v= 331 m/s + 11.8 m/s
v= 342.8 m/s

Δt= 0.54 m ÷ 342.8 m/s = 0.0015752 s

But this isn't the right answer
Duplicate threads merged. Please take care not to multiple post.
 
  • #10
1,137
0
OH YES!!! That eqn is for sound!!!!
 

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