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Focus of a plane mirror

  1. Jan 13, 2013 #1
    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 ?
  2. jcsd
  3. Jan 13, 2013 #2
    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?
  4. Jan 13, 2013 #3


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    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.
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