Discussion of the section on images Discuss some of these questions with the people in your group:
  1. We do not recommend using a lens to try to start a fire. The little spot of light is very bright -- too bright to look at, really. But let's discuss the theory for a minute. All the light that hits the lens is delivered to the image. If the image is smaller, the concentration of the light is greater; if the lens is larger, more energy is collected. Thus the relevant feature is the ratio of the diameter of the lens to the diameter of the image. Then which of the lenses you have is the best for this purpose, or are they all pretty much the same?
  2. Although we should never look at the sun, sometimes we want to know what's happening in that direction. For example, we would want to observe (somehow) a partial solar eclipse; sometimes, too, there are visible sunspots, which are regions on the face of the sun that are somewhat cooler than the rest. One way to do this is to make an image of the sun on a screen, using a lens. If we want the image to be big (so we can see the sunspots) and not too bright (so we can look at it), what kind of lens do we need? What does your sun viewer look like?
  3. Margie has a great idea how to decorate her living room for when she hosts the bridge club next week: she will draw hearts and spades on the light bulbs, and then use lenses to project these pictures onto the lampshade and the ceiling. Easy to do, cheap, and after the party she can just wash the pattern off. Will this work at all? What kinds of things can go wrong? I suspect Margie will need a lot of advice from an expert like you. .
  4. Make a Model Camera (activity Lenses #8 in the manual). You have several lenses to choose from, and there is a plastic lid in the kit that will make a screen. You only need a box of the right size.
Please send us your discussion of two of these questions (or a description of how you made your model camera, and what you observed).  Don't forget to tell us who is in the group.
If there is something that you don't understand about images, Ask us!
This is the end of this section. Please note that these activities are written up (in slightly different form) in the manual (in the Lenses and Curved Mirrors sections).
The next section is about light energy.