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Homework Help: How do I know if the image is real or virtual?

  1. Jun 7, 2017 #1
    1. The problem statement, all variables and given/known data
    I know that the object distance is 15 using the equation m = - (v/u)
    (+ or - depending on real / virtual) 2 = (+ or -) 30/u
    u = 15

    However how do I know if the image is real or virtual?

    2. Relevant equations
    m = - (v/u)

    3. The attempt at a solution
  2. jcsd
  3. Jun 7, 2017 #2
    Have you tried drawing the diagram, something like this: u14l5c1.gif

    Where would the image have to be to be bigger than the object?

    Which side is known as the real side, which side is known as the virtual side and why?
  4. Jun 7, 2017 #3
    How do I draw the diagram when I don't know if the object is within / outside the focal length?
    Also I used to think that because the image is bigger it must be virtual, however there are some diagrams on the internet where the image is bigger and the object is outside the focal length, like here: u14l5da6.gif
  5. Jun 7, 2017 #4
    "the lens is used as a magnifying glass"- usually when using a magnifying glass is the image virtual or real?
  6. Jun 7, 2017 #5
    As far as I know, in a converging lens, only when the object is between the optical centre and the focal length that the image is virtual (i.e. the setting used in a magnifying glass).
  7. Jun 7, 2017 #6
    Ah yeah the magnifying glass part makes sense - thanks for explaining
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