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Homework Help: Simple ray Optics question please help!

  1. Jan 28, 2012 #1
    θ1. The problem statement, all variables and given/known data

    The sun of (diameter D) subtends an angle of θ radians at the pole of the concave mirror of focal length f. The diameter of the image of the sun formed by mirror is _____

    2. Relevant equations


    3. The attempt at a solution
    confused with question. Either i am getting zero or infinity(sun is too large!)..
  2. jcsd
  3. Jan 28, 2012 #2
    The sun can be taken to be at infinity so the image of the sun will be formed...... where?
    Light rays striking the centre of the mirror (from the top/bottom of the sun) will be reflected at same angle.
    Can you get it from this?
  4. Jan 28, 2012 #3
    when light strike at the pole of the concave mirror they are reflected like plane mirror. So No image should form?
    Am i correct?
  5. Jan 29, 2012 #4


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    Homework Helper

    No, only one ray from each point on the sun strikes the pole of the mirror. All the other rays strike somewhere else.
    You do know what direction one other special ray will reflect, and every other ray from a given point on the sun will reflect through that same point - forming an image of that point.
    Choosing a point on the "top" of the sun, and another on the "bottom"of the sun will enable you to locate the extent of the image of the sun.
  6. Jan 29, 2012 #5


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    Homework Helper

    btw - have you ever seen an image of the sun "reflected in the side of a sky scraper"?
    That should answer your question about whether an image is formed after reflection in a plane mirror.
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