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View Full Version : Examine the rays hitting the concave mirror below. F is the focal point and C is the


xMerlina
May 7, 2011, 04:12 PM
So... my teacher never taught me how to figure this out O_O I know what these angles are, but I have no clue how to determine their relationship.

http://www.flickr.com/photos/62288400@N06/5697691436/in/photostream

1. If ray Z is the incident ray then ray Q is the reflected ray.
2. If ray Z is the incident ray then ray R is the reflected ray.
3. If ray L is the incident ray then ray Q is the reflected ray.
4. If ray Q is the incident ray then ray M is the reflected ray.
5. If ray M is the incident ray then ray R is the reflected ray.
6. If ray Z is the incident ray then ray R is the reflected ray.

Unknown008
May 8, 2011, 01:57 AM
Your question in the title got cut because it accepts limited characters...

Anyway, if F is the focal point, then any ray coming parallel with the principal axis will be reflected through the focal point, and as such, any ray coming through the focal point will be reflected parallel to the principal axis.

I guess it's a 'True/False' question, so I'll let you deduce for now which of them are correct and which are not. Post what you get! :)

xMerlina
May 8, 2011, 07:14 AM
Oh, oops. Yeah, it's a true/false question. The part that got cut off was C is the center of curvature. I'll give it a shot, though this is a lot harder since there's only one parallel ray...

1. false
2. false
3. true
4. false
5. true (this is the only one I'm fairly certain about)
6. false

Unknown008
May 8, 2011, 07:35 AM
1. Could very well be true. Compare Z to M. M would give R, Z would give something higher than R, which is Q.

2. See 1. so, yes, it's false.

3. Ah no, that's false. L comes 'above' the focal point, and hence, it will go down instead of higher up.

4. M goes through the focal point, hence Q should be dead horizontal, hence yes, false.

5. Yes, correct :)

6. Correct, Z has to pass through the focal point to be reflect through R.

Not bad :)

xMerlina
May 8, 2011, 07:39 AM
Ohh, I think I get it now. Your explanations were really helpful. Thanks so much!

Unknown008
May 8, 2011, 07:56 AM
You're welcome! :)

Thanks for the thumbs up ;)