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

[Mphisto]

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?

Homework Equations

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

 

[ehild]

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

 

[Mphisto]

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...

 

[Doc Al]

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?

 

[Mphisto]

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

 

[Doc Al]

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.

 

[Mphisto]

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)

 

[Doc Al]

"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?

 

[Mphisto]

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

 

[Doc Al]

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.)

 

[Mphisto]

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?

 

[Doc Al]

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.

 

[Mphisto]

No. The normal is perpendicular to the tangent line.

Oh ok, I got it

Thank you!