Sunday, April 25, 2010

Your whole world turned upside down

Imagine your whole world turned upside down. This contrived photo of my backyard upside down illustrates simple physics concepts of optics as they apply to lenses. All that is needed to test this concept is a transparent glass with a somewhat spherical or convex shape and some water. When this glass is filled with water, the water takes the shape of the glass and acts as a convex lens. When an object is viewed through a convex lens, the resulting image is smaller and inverted. You can also see that the empty half of the glass seems to be the same shape as the filled half. Why, then does it not invert the image? you may ask. Well, a convex or biconvex lens consists of a solid, transparent material that has a center that is thicker than this ends. Since the empty part of the glass is not solid, it is not a single convex or converging lens, meaning that it cannot create the same inverted resultant image as the water does. There are lenses formed by the glass, however. One side acts as a positive meniscus lens, converging the light which passes through. The other acts as a negative meniscus lens, diverging the already converged light, making it seem like the upper half of the glass had no effect on the light.


  1. What a fantastic description of a simple lens! How much simpler can we get than a glass of water! There's so much physics involved, though. I love it.

    I also really like that the foreground is in focus while the background is out of focus. Using depth-of-field in photos is a great way to add interest and you definitely made it interesting.

  2. What a very nice yard! As I type this comment, I am sitting on my back porch watching cows and horses walk by. But I digress.

    You have shown an interesting demonstration of two refraction situations. The physics geek in me likes to draw ray diagrams of these types of complex refraction situations. Have you tried doing that with your example?

    Keep up the great work!

  3. Excellent picture!
    Your physics explanation needs some clarification.
    First, your claim that in a "convex lens, the resulting image is smaller, virtual, and inverted." is incorrect.
    Virtual images are not inverted. Convex lenses are converging so the only case when they produce a virtual image (when object is inside the focal length) the image is upright and larger than the actual object. This is what we call a 'magnifying glass'. So how do you explain the image?