# Time it takes for light to travel 54 cm

## 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

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HallsofIvy
Homework Helper
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?

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

is the answer : 2.626 x 10^-9 ???

is the answer : 2.626 x 10^-9 ???
yes! can you show me how to do it!

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

ehild
Homework Helper
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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

berkeman
Mentor
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).

berkeman
Mentor
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