Why Light Doesn't Deviate When Entering Semi-Circular Glass?

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Light does not deviate when entering a semi-circular glass block if it strikes the surface perpendicularly, meaning the angle of incidence is zero. When the light ray is directed along the radius of the circle, it is normal to the surface, allowing it to pass straight through without refraction. However, refraction occurs when the light exits the block at the second surface. The discussion clarifies that the normal line is perpendicular to the tangent at the point of entry, which is crucial for understanding the behavior of light in this context. Overall, the key takeaway is that the angle of incidence determines whether light will deviate upon entering a medium.
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Homework Statement


Well, this is not really a homework question but something I wanted to find out. Basically, Why there is no deviation of light ray when it enters a semi circular glass block?


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The Attempt at a Solution


I thought light ray would not be deviated only when it enters another medium perpendicular to boundary. So why would it not be deviated when it enters the a semi circular glass block?

Thank you :smile:
 
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Hi, Mphisto,

The light ray will deviate if it enters at an angle with respect to the surface normal. Why do you think it will not?

ehild
 


ehild said:
Hi, Mphisto,

The light ray will deviate if it enters at an angle with respect to the surface normal. Why do you think it will not?

ehild

I don't get your post...
 


Mphisto said:
Basically, Why there is no deviation of light ray when it enters a semi circular glass block?
How is the light entering the block? What angle is it making with the normal to the surface?
 


Doc Al said:
How is the light entering the block? What angle is it making with the normal to the surface?

http://t2.gstatic.com/images?q=tbn:ANd9GcRhvx6-lH4b3Dpe1otCjmmVHn_bcsWOpLUnEf-_A3IhQQON_YG0
Taken from google, as you can see the incident ray passes straight through the glass block
 
Last edited by a moderator:


Mphisto said:
Taken from google, as you can see the incident ray passes straight through the glass block
At the first surface (air to glass), the angle with the normal is zero so it passes straight through. Is that what you mean? (The ray of light is directed along the radius, so it is normal to the surface.)

Of course it undergoes refraction when it leaves the block.
 


Doc Al said:
At the first surface (air to glass), the angle with the normal is zero so it passes straight through. Is that what you mean? (The ray of light is directed along the radius, so it is normal to the surface.)

Of course it undergoes refraction when it leaves the block.

"angle with the normal is zero"? shouldn't the light ray be refracted at the first surface? (air to glass)
 


Mphisto said:
"angle with the normal is zero"?
That's correct.
shouldn't the light ray be refracted at the first surface? (air to glass)
What's the angle of incidence?
 


Doc Al said:
That's correct.

What's the angle of incidence?

I am not sure... since it's curved i don't know how the normal would be placed there
 
  • #10


Mphisto said:
I am not sure... since it's curved i don't know how the normal would be placed there
Note that the incoming light ray is aimed along the radius of the circle and is thus normal to the surface. (Imagine a tangent line to the semi-circle drawn at the point where the light enters--take that as the surface.)
 
  • #11


Doc Al said:
Note that the incoming light ray is aimed along the radius of the circle and is thus normal to the surface. (Imagine a tangent line to the semi-circle drawn at the point where the light enters--take that as the surface.)

So basically the normal of first surface is like a tangent line to the semi-circle? am I right to say that?
 
  • #12


Mphisto said:
So basically the normal of first surface is like a tangent line to the semi-circle? am I right to say that?
No. The normal is perpendicular to the tangent line.
 
  • #13


Doc Al said:
No. The normal is perpendicular to the tangent line.

Oh ok, I got it :biggrin:

Thank you!
 
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