Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: The Focal Length of a Lens?

  1. Apr 25, 2010 #1
    1. The problem statement, all variables and given/known data

    An object is located 26.0cm from a certain lens. The lens forms a real image that is twice as high as the object.

    (i) What is the focal length of this lens?

    (ii) Now replace the lens used in Part 1 with another lens. The new lens is a diverging lens whose focal points are at the same distance from the lens as the focal points of the first lens. If the object is 5.00cm high, what is the height of the image formed by the new lens? The object is still located 26.0cm from the lens.

    2. Relevant equations

    Since the image is real and 2X as large, the magnification m = -2. The formula
    m = -i/o
    1/o + 1/i = 1/f

    3. The attempt at a solution

    After attempting part 1 i got 5.77cm which is incorrect.
  2. jcsd
  3. Apr 25, 2010 #2
    You got to take care of the sign convention.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook