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Thread: Concave calculation

  1. #1 Concave calculation 
    Forum Freshman monaro_waky's Avatar
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    Aug 2006
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    Hi everyone I got another problem for you.
    Any way i've been trying to figure this question out for the past hour
    A girl wants to see her tear duct by looking into a concave mirror, with a focal point of 1m and she wants the magnification of her tear duct to be 4.
    So I've been re-aranging the formulas but still dont get it.
    M=4
    f=1m
    u=?

    1=1+1
    f ~v~u

    and

    M=|v|
    ~~|u|

    Don't pay attention to the ~ i just put it there for spacing.
    Thanks


    There are no such things as applied sciences, only applications of science.
    Louis Pasteur (1822 - 1895)
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  3. #2  
    Forum Professor river_rat's Avatar
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    Been a while since ive done this type of question but this is what i get:

    1/f = 1/u + 1/v => 1 = 1/u + 1/v

    But 4 = v/u => v = 4 u which gives that 1 = 1/u (1 + 1/4)

    i.e. u = 5/4 and v = 5

    I cant remember if this is right though - but thats the maths for the equations you gave.


    As is often the case with technical subjects we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or comprehensible but wrong.
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