Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Convex mirror, and you point a light at it horizontally

  1. May 9, 2004 #1


    User Avatar
    Science Advisor
    Homework Helper

    If you have a convex mirror, and you point a light at it horizontally, does the light always reflect through the focal point? (the point halfway on the line connecting border and the center, parallel to the light's initial path)

    I remember learning this, but I think of a mirror in the shape of a semi-circle, and you point the light at the bottom, it only bounces along the edge...?
  2. jcsd
  3. May 9, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Horizontal (parallel to the axis) rays will reflect from a convex mirror so that they appear to originate from the focal point.
  4. May 9, 2004 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Also, this is only true in the limiting case when the size of the mirror (aperture) is small compared to the radius of curvature. So, when you take a semi-circular (actually hemispherical) mirror, it is no longer small compared to R. So, the behavior will be different, and hence glancing is not a violation. It's just outside the domain that the above rule applies to.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook