There are many household devices that manipulate light, and one of the most familiar is a magnifying glass. A magnifying glass bends light rays toward one another as they pass through it. In this chapter, we’ll see how a simple converging lens of this sort can magnify an object or cast its image onto a light-sensitive surface. For the moment, we’ll use it to cast the image of a window onto a wall.
Take a magnifying glass to a room with a bright window and turn off the lights. Hold the magnifying glass near the wall opposite the window and move the glass toward or away from the wall until you see a window-shaped pattern of light appear on the wall. Once that pattern is visible, carefully adjust the magnifying glass’s orientation and distance from the wall to obtain the sharpest image of the window. You’ll probably also see images of objects outside that window, but you’ll have to move the magnifying glass to sharpen those images.
1.Which way did you move the glass to get it to focus, and why can’t all the images be sharp at the same time?
2.You can project images of other brightly illuminated objects on a sheet of white paper. What features of the lens determine the sizes of those images?
3.What determines their orientations?
4.Block part of the lens, and notice how it affects the images.
5.Try to form images of objects at different distances from you. Do they all form images simultaneously, or do you have to adjust the lens somehow to bring each image into sharp focus?
6.If you had a larger magnifying glass, how would this change what you see?
Concluding Everyday Life Task:
7.Name two examples from your personal daily life where you see a phenomenon like this. Try not to give standard examples as given in the textbook but make it a personal challenge to discover new examples in your daily life!
We see light because it stimulates cells in our eyes. This stimulation is an example of light’s ability to influence chemistry. And because our eyes are able to distinguish among the different wavelengths of light, we perceive colors. Sunlight normally appears uncolored because it contains a rich mixture of wavelengths that our eyes interpret as whiteness. However, there are situations in which sunlight becomes separated into its constituent colors.
You can observe this separation of colors by looking at sunlight passing through a cut crystal glass or bowl, or by reflecting sunlight from a CD or DVD. Hold the object in direct sunlight and observe the light that it redirects toward your eyes or projects onto a white sheet of paper nearby. While some of the light you see will still be white, you should see colors as well.