Conceptual Physics (12th Edition)

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

Chapter 36 - Think and Explain: 41


No, it won't be, though the difference won't be noticeable. Strictly speaking, your friend receives red-shifted light.

Work Step by Step

The light is climbing against the gravitational field. The photons lose energy. The energy of a photon is given by E = hf, where h is Planck's constant. If the energy of light is lowered, as in traveling upward in a gravitational field, its frequency is lowered (the light is said to be red-shifted). The frequency your friend receives is lower than the frequency you sent.
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