Register to reply

Focus of a plane mirror

by Sam Morse
Tags: focus, mirror, plane
Share this thread:
Sam Morse
#1
Jan13-13, 02:28 AM
P: 15
I read somewhere that the focus of a plane mirror is at infinity because rays after reflection from a plane mirror don't intersect anywhere. But why can't the focus be virtual as in case of concave mirror ?
Phys.Org News Partner Physics news on Phys.org
Symphony of nanoplasmonic and optical resonators produces laser-like light emission
Do we live in a 2-D hologram? New Fermilab experiment will test the nature of the universe
Duality principle is 'safe and sound': Researchers clear up apparent violation of wave-particle duality
Vagn
#2
Jan13-13, 02:52 AM
P: 295
Quote Quote by Sam Morse View Post
I read somewhere that the focus of a plane mirror is at infinity because rays after reflection from a plane mirror don't intersect anywhere. But why can't the focus be virtual as in case of concave mirror ?
When considering where the focal point is we use two parallel rays of light incident on the mirror, how will these two rays be reflected from a plane mirror?
Low-Q
#3
Jan13-13, 06:00 AM
PF Gold
Low-Q's Avatar
P: 244
Quote Quote by Sam Morse View Post
I read somewhere that the focus of a plane mirror is at infinity because rays after reflection from a plane mirror don't intersect anywhere. But why can't the focus be virtual as in case of concave mirror ?
The two parallell rays of light we use to determine the focal distance will still be parallell and with the same distance from eachother at infinity.
Saying that the focal point is present at infinity is a nonsense paradox of the terminology infinity just as my above explanation. The focal point could likely be behind the mirror, saying that the two parallell rays would be separated infinitly from each other at infinity in front of the mirror.


Register to reply

Related Discussions
Curvature to mirror and focus light? General Physics 47
Need help on Plane Mirror Introductory Physics Homework 2
Images With Plane Mirror Introductory Physics Homework 2
Focus moonlight wth a mirror system Introductory Physics Homework 7
Where is the principle focus of a plain mirror? General Physics 5