Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 26 - Think and Solve: 38

Answer

The penumbra has three times the diameter of the ball.

Work Step by Step

See the diagram. The umbra has the same diameter (EF) as the ball because the bulb is the same size as the ball. Triangles ABC and ADF are similar, with sides in the ratio of 1 to 2. Triangles ABC and BDE are congruent. This means that DE = EF = FG. The penumbra has three times the diameter of the ball.
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