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Homework Help: Maximum magnifacation

  1. Aug 5, 2007 #1
    1. The problem statement, all variables and given/known data

    A boy scout starts a fire by using a lens from his eyeglasses to focus sunlight on kindling 5.2 cm from the lens. The boy scout has a near point of 15.2 cm. When the lens is used as a simple magnifier, give values for the following conditions. (Hint: Assume a "normal" eye.)
    (a) What is the maximum magnification that can be achieved

    (b) What is the magnification when the eye is relaxed

    2. Relevant equations

    Mmax= 1+ 25/q
    Mrelaxed = 25/q

    3. The attempt at a solution

    I have tried 1/5.2 + 1/-(15.2-5.2) = 1/f
    then I tried 1+ 25/10.83= 3.3 and 1+15.2/10.83=2.4 and both are wrong?
    Please help
  2. jcsd
  3. Aug 6, 2007 #2
    You're using the mirror formula. You have to use the LENS formula. 1/v-1/u=1/f. Be careful about the signs of v and u. The direction of the ray of light is +ive and opposite is -ive.
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