Radiation intensity and distance?

AI Thread Summary
The discussion focuses on calculating the time a light ray spends inside a plastic block with an index of refraction of 1.70. Using Snell's law, the angle of refraction is determined to be approximately 67.8 degrees. To find the speed of light in the plastic, the index of refraction is used, as it defines the relationship between the speed of light in a vacuum and in the material. The length of the light's path through the block must also be calculated using trigonometry. Understanding these concepts is essential for solving the problem effectively.
gigli
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Homework Statement


A light ray enters the plastic block in the illustration at an angle of 33.0° and then exits the opposite side. The long side of the block has a length of 0.670 m and its index of refraction is 1.70. For how much time is the light ray inside the block?

https://www.physicsforums.com/attachment.php?attachmentid=15094&stc=1&d=1219187822

Homework Equations


Snell's law:
nisin\thetai=nrsin\thetar
n=index of refraction
\theta=incident angle from normal


n plastic=1.70
n air = 1.00

The Attempt at a Solution


According to Snell's law:
(1.70)*sin(33)=(1.00)*sin(\theta)
0.92588636=sin(\theta)
arcsin(0.92588636)=\theta = 67.8023923 degrees

And the speed of light is 2.998*10^8 m/s.

But after that I am not sure where to proceed! Can anyone help me figure this one out?
 
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You need to know two things to solve this problem.

1. The speed of light in the plastic block.

Do you know how to find this?

2.You need to know the length of the path traveled through the block.

You should be able to find this using the angle obtained from Snell's law and some trigonometry, but I can't say for sure if you don't post the actual figure in question.
 
How do I determine the speed of light inside the plastic?

And I posted a diagram:
https://www.physicsforums.com/attachment.php?attachmentid=15094&stc=1&d=1219187822
 
Got it. Speed of light in plastic. Roger. Appreciate it
 
Last edited:
gigli said:
How do I determine the speed of light inside the plastic?

The only property you're given about the material is its index of refraction. What is the definition of the index of refraction?
 
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