Use ray diagrams to locate the images of the following objects (1) an object that is 10 cm from a converging lens of 15.0 cm focal length,

Question

Direction: Use ray diagrams to locate the images of the following objects (1) an object that is 10 cm from a converging lens of 15.0 cm focal length, (2) an object that is 10 cm from a diverging lens of -15 cm focal length (3-4) Calculate the image location of parts (1) and (2) using the thin-lens equation (5-6) How large is the image formed in parts (1) and (2). you may use the following equations below:

1/f = 1/d_o + 1/d_i (Eq. 1)

m = hi/ho = -di/do (Eq 2)

Answer 1

Look Jayvee D.,

You can either approach physics as "plug-into-equations" or as "apply basic principles to solve". With the first approach, it's very fast, but you run the risk of mis-remembering an equation, or mis-interpreting the variables in an equation. Usually this is disastrous.

With the second approach, you remember a few basics, and write the equations you need in the spot. So here in optics, for example, with converging lenses, all you need to remember is that the inverse of distances is what matters, and that the lens converges parallel rays (d = infinity) to the focal distance on the other side (d=f). Co-incidentally, that means that an object exactly 2 focal distances from the lens, will have an image 2 focal distances from the lens on the other side -- since 1/(2f) + 1/(2f) = 1/f . For diverging lenses, there is a far-object equation (essentially, near-parallel rays are being diverged as if from a virtual image just inside the focal point), and you just need the distance reference points stored mentally!

The same approach applies to parabolic mirrors, by the way.

It may help you to sketch your ray-tracings, for a while, until you get really quick at figuring out what you need to use to set up your equations.

-- Cheers, --Mr. d.