Incidence, Refraction, Critical Angle

  • Thread starter Air
  • Start date
  • #1
Air
202
0

Homework Statement


Travellers in hot places often think that they see water in the distance, when there is nothing but land there. This effect is called a mirage. The air near the ground is very hot, and light reflects off the top of this layer of hot air. The diagram below shows how you could demonstrate the effect in a laboratory.

AirGlassBlock.jpg


On the diagram, draw appropriate normals and mark:
  • An angle of incidence, labelled I,
  • An angle of refraction, labelled R, and
  • An angle labelled G which you know is greater than the critical angle.


2. The attempt at a solution
AirGlassBlockMyAnswer.jpg


^ Is it correct?
 

Answers and Replies

  • #2
Hootenanny
Staff Emeritus
Science Advisor
Gold Member
9,621
6

Homework Statement


Travellers in hot places often think that they see water in the distance, when there is nothing but land there. This effect is called a mirage. The air near the ground is very hot, and light reflects off the top of this layer of hot air. The diagram below shows how you could demonstrate the effect in a laboratory.

AirGlassBlock.jpg


On the diagram, draw appropriate normals and mark:
  • An angle of incidence, labelled I,
  • An angle of refraction, labelled R, and
  • An angle labelled G which you know is greater than the critical angle.


2. The attempt at a solution
AirGlassBlockMyAnswer.jpg


^ Is it correct?
Looks good to me :approve:
 
  • #3
Air
202
0
I was confused if G was just as the ray left the glass block. So, it is correct, that it occurs during total internal reflection?
 
  • #4
Hootenanny
Staff Emeritus
Science Advisor
Gold Member
9,621
6
I was confused if G was just as the ray left the glass block. So, it is correct, that it occurs during total internal reflection?
I'm sorry I'm not sure what you mean. You know that G must be greater than the critical angle because TIR occurs.
 
  • #5
Air
202
0
So, is G the angle of incidence for total internal reflection to occur.

Isn't critical angle when incident angle equal reflected angle? :confused:
 
  • #6
Hootenanny
Staff Emeritus
Science Advisor
Gold Member
9,621
6
So, is G the angle of incidence for total internal reflection to occur.

Isn't critical angle when incident angle equal reflected angle? :confused:
No, all you can conclude from the diagram is that G is greater than the critical angle since we have TIR. Furthermore, the incident angle is always equal to the reflected angle.
 
  • #7
Air
202
0
If I drew G on the other side of the normal inside the glass block (where total internal reflection occurs), would that have been correct too? Or, is it always the angle from the normal line when it is incident ray?
 
  • #8
Hootenanny
Staff Emeritus
Science Advisor
Gold Member
9,621
6
If I drew G on the other side of the normal inside the glass block (where total internal reflection occurs), would that have been correct too? Or, is it always the angle from the normal line when it is incident ray?
The critical angle is always measured from the normal to the incident ray. However, in this case you know that since the ray is reflected both the angles on either side of the normal must be equal, therefore it is equally correct to mark G as the angle between the reflected ray and the normal line.
 

Related Threads on Incidence, Refraction, Critical Angle

  • Last Post
Replies
6
Views
3K
Replies
3
Views
7K
  • Last Post
Replies
3
Views
5K
  • Last Post
Replies
1
Views
3K
Replies
3
Views
4K
Replies
1
Views
6K
Replies
6
Views
12K
Replies
1
Views
6K
Replies
6
Views
5K
Replies
16
Views
2K
Top