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Old May 11th 2008, 12:14 PM   #1
Air
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Critical Angle, Incident Angle, Refracted Angle...

Q: Farmers can choose the best time to harvest some fruits by measuring how much sugar their juice contains. The concentration of sugar in the juice alters its refractive index which can be measured with a refractometer. Figure 1 shows a beam of light entering a refractometer. The juice is placed on top of the prism.


A student uses a prism to investigate this effect in the school laboratory. A layer of juice is trapped between the prism and a microscope slide. Figure 2 below shows a ray of light hitting the surface between the prism and the juice at the critical angle.


Mark the following angles on figure 2 above: the critical angle C, an incident angle i, a refracted angle r.

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Old May 11th 2008, 07:49 PM   #2
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Originally Posted by Air View Post
Q: Farmers can choose the best time to harvest some fruits by measuring how much sugar their juice contains. The concentration of sugar in the juice alters its refractive index which can be measured with a refractometer. Figure 1 shows a beam of light entering a refractometer. The juice is placed on top of the prism.


A student uses a prism to investigate this effect in the school laboratory. A layer of juice is trapped between the prism and a microscope slide. Figure 2 below shows a ray of light hitting the surface between the prism and the juice at the critical angle.


Mark the following angles on figure 2 above: the critical angle C, an incident angle i, a refracted angle r.

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My Problem: This is another one of the question that I do not understand. Can someone complete the diagram? Thanks in advance.
You have two refraction points and three internal reflections. The total internal reflections work the same way mirrors do: angle of incidence is equal to the angle of reflection. I have provided two diagrams below: the first is for refraction and the second (on the right) is for internal reflection.

-Dan
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Critical Angle, Incident Angle, Refracted Angle...-refraction.jpg  
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Old May 12th 2008, 10:04 AM   #3
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Originally Posted by topsquark View Post
You have two refraction points and three internal reflections. The total internal reflections work the same way mirrors do: angle of incidence is equal to the angle of reflection. I have provided two diagrams below: the first is for refraction and the second (on the right) is for internal reflection.

-Dan
Can you complete the diagram so I can see how it is?
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Old May 12th 2008, 08:28 PM   #4
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I can't upload anything from this computer. (It has an innocuous virus, but it's still a virus.) However I don't see where the confusion is here. As the ray enters the prism (the incoming ray on the left side) we have a refraction. When the ray strikes the inner surface of the prism we have a total internal reflection etc. The angles of incidence, refraction, and reflection are simply the angles of those rays from the normal to the relevant surface.

If you really need it I can post the diagram sometime tomorrow.

-Dan
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Old May 13th 2008, 06:07 AM   #5
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It's a little messy, but here is part of your ray diagram.

-Dan
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Critical Angle, Incident Angle, Refracted Angle...-ray.jpg  
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