# Light is Reflecting-EASYYYY PROBLEM! but help needed.

1. Jan 9, 2008

### physicsbhelp

[SOLVED] Light is Reflecting-EASYYYY PROBLEM! but help needed.

1. The problem statement, all variables and given/known data

Figure 33-47 shows light reflecting from two perpendicular reflecting surfaces A and B. Find the angle between the incoming ray i and the outgoing ray r'.
The figure is attached to this thread!

2. Relevant equations

angle of incedence = angle of reflection

3. The attempt at a solution

don't know where to start from

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2. Jan 9, 2008

### Dick

The two acute angles in a right triangle sum to 90 degrees. They are complementary. Use that.

3. Jan 9, 2008

### physicsbhelp

oooo well thank you Dick, but how in the world can you find out those two angles, if no other values of angles are given. like i no the normal line equals to 90 degrees also, but how can you find the angles.

4. Jan 9, 2008

### Dick

The angle between the incoming and the outgoing ray is the difference between the angle theta in your picture and the angle r' makes with the horizontal surface B (call it phi). Start labelling all of the angles you can find as either theta or 90-theta. You should be able to show phi=theta.

5. Jan 9, 2008

### physicsbhelp

and congratulations Dick on receiving the 2007 PF Award!

6. Jan 9, 2008

### Dick

Thanks for the congrats. Yes, theta and phi are the angles the incoming and outgoing make with a horizontal line. If those are equal, they are parallel.

7. Jan 9, 2008

### physicsbhelp

whoA! wait a second. i thought tha theda made an angle with the vertical line and normal line. like in teh diagram= that shows what theda is.

8. Jan 9, 2008

### Dick

'teh diagram' that I'm looking at shows theta as the angle between the incoming ray and the normal to the vertical reflector - which is horizontal.

9. Jan 9, 2008

### Dick

You are asked for the angle BETWEEN incoming and outgoing. If they are parallel, the angle between them is zero.

10. Jan 9, 2008

### Dick

I think you just don't understand the question. You can't determine any of the angles in the problem. You aren't given any. All you can say is what the relation is between the angles. If you understand that the incoming and outgoing ray are parallel, then you are DONE. They make the same angle with the horizontal. The angle between them is ZERO. Write that answer down along with why you believe it and turn it in.