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Optics (Reflection)

  1. Aug 1, 2014 #1
    The size of image formed by a concave mirror is proportional to R^n where R is radius of curvature. Find n.
    Cannot understand how to proceed. Need help.
     
  2. jcsd
  3. Aug 1, 2014 #2

    rude man

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    It's not. The size of the image is a function of R and the distance between the object and the mirror. Even for a fixed object distance the size of the image is a function of R but not proportional to R.
     
  4. Aug 1, 2014 #3
    Ok thnx.....but what if the object is at infinite position??
    .....btw answer given in the book is 1
    n=1
     
  5. Aug 1, 2014 #4

    rude man

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    That's right. For the object distance >> R the answer is proportional to R1. But not R = ∞ since then the image size is zero unless it's also infinite in size!

    So, to continue:

    1. what is the simple equation relating object o and image i distances, and the radius R?
    2. what is the expression for magnification?
    3. what is #2 when o >> R?
     
    Last edited: Aug 1, 2014
  6. Aug 1, 2014 #5
    Cannot proceed..... 1/v + 1/u = R/2
    Now can we omit 1/u cause its too small?
    Then eqn bcums v=2/R....from this it is clear that image is at focus
    Now what ?
     
  7. Aug 1, 2014 #6
    Btw i think i proceeded a bit further.....Now magnification is very small...
    Now size of image/size of object = magnification(very small)
    or, size of image = magnification * size of object
    or, k(R^n) = magn * size of objct
    or, magn = { k(R^n) } / Size of objct
    This magn is very small, for it to be very small, n needs to be least....therefore n = 1
    Is that it?
     
  8. Aug 2, 2014 #7

    rude man

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    Your equation is dimensionally incorrect. Which means it is incorrect. Fix it!
     
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