A flat piece of glass

2012-12-06 10:34 pm

A flat piece of glass covers the top of a vertical cylinder
that is completely filled with water. If a ray of light traveling
in the glass is incident on the interface with the water at an
angle of 36.0 degree , the ray refracted into the water makes an
angle of 49.4 degree with the normal to the interface.

What is the smallest value of the incident angle for which none
of the ray refracts into the water?

Express your answer with the appropriate units.

My answer:

n sin 36 = 1.333 sin 49.4 , where n is the index for
refraction for the glass.

n= 1.7219

And then I have no idea.

回答 (1)

天同

2012-12-06 11:41 pm

✔ 最佳答案

You have already got the refractive index for the glass plate, n(g) = 1.7219

For no refraction in water, total internal reflection occurs.
Hence, 1.7219.sin(c) = 1.333.sin(90)
where c is the incident angle (critical angle) where total internal refraction occurs.
sin(c) = 1.333.sin(90)/1.7219 = 0.7741
c = 50.73 degrees

Therefore, the smallest incident angle should be 50.73 degrees.

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