1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Convex mirror reflection

  1. Mar 2, 2014 #1
    1. The problem statement, all variables and given/known data

    For self study, I've been trying to understand my convex mirror.
    Some online instruction I've been following states that if an incidence ray (red line in my model, below) parallel to the principal axis (black line) hits a convex mirror (full curvature outlined in black, centre C), the reflected ray (purple) extended back passes through the focal point (F).

    2. Relevant equations
    In my graphed model below, the points & vectors are
    centre of curvature, C is at origin
    focal point, F = (25,0)
    normal to incident, N = (0.91128...,-0.41178...)
    incident, I = (-1,0)
    reflected, R = (0.66087...,-0.75049...)

    3. The attempt at a solution


    I graphed my model (above) but the reflected vector does not run exactly through my focal point as expected. I've checked this is not simply a rounding error (or any other obvious mistakes). There are also other problems when I plot more incident vectors emanating from the same point (not shown): the reflected vectors do not converge on a virtual image point as expected. Something crucial is missing from my understanding of this problem.
  2. jcsd
  3. Mar 2, 2014 #2


    User Avatar
    Homework Helper

    In the concave mirror, the reflected ray will pass through F if the ray is parallel to the principle and close to the principle axis. Such rays are called par axial rays.
  4. Mar 3, 2014 #3
    Are you just saying the principle is an approximation. I.e. in fact it never passes exactly through F at all (except of course when the incident ray is along the principal axis), but the reflected ray gets very close to F when the incident is close to the principal axis
  5. Mar 3, 2014 #4


    User Avatar
    Homework Helper

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted