## Conceptual Physics (12th Edition)

Published by Addison-Wesley

# Chapter 32 - Think and Explain - Page 613-614: 33

#### Answer

The frequency of every photon is related to its energy by E = hf.

#### Work Step by Step

If two frequencies add up to a third frequency: $$f_{1} + f_{2} = f_{3}$$ then the photon energies associated with those frequencies obey a similar relationship: $$h f_{1} + h f_{2} = h f_{3}$$ $$E_{1} + E_{2} = E_{3}$$ In a transition that skips an energy level, such as the one from n = 3 to n = 1 shown in Figure 32.9, energy conservation requires that the emitted energy be the same as the sum of the emitted energies if it made 2 transitions, from n = 3 to n = 2 and then from n = 2 down to n = 1. Therefore the emitted photon frequency for the large transition will be the sum of the photon frequencies emitted during the two other transitions. This is the Ritz combination principle.

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