2. How soon after any great disturbance takes place on the sun, 93,000,000 miles distant, can it be seen upon the earth?
3. Construct a diagram of the moon's shadow. How much of the sun can one see when in the moon's umbra? When in its penumbra? Have you ever been in either? When? Have you ever been in the earth's umbra? In its penumbra?
4. Explain, using a diagram, the formation of an inverted image by a small aperture.
5. If the sun is 45 degrees above the horizon, what is the height of a pole casting a shadow 60 ft. long?
6. If a shadow 6 ft. long is cast by a 10-ft. pole standing vertically upon a walk, how tall is the tree whose shadow is 42 ft. long, both measurements being made at the same time?
7. Why are the shadows caused by an electric arc lamp so sharply defined?
8. Why should schoolroom windows be all on one side and reach to the ceiling?
9. What is the relation between the size of an image and its distance from the aperture forming it? Can you prove this by geometry?
10. What are silhouettes and how are they produced?