SAT Subject Physics Practice Question 139: Answer and Explanation

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Question: 139

2. A metal whose work function is 6.0 eV is struck with light of frequency 7.2 × 1015 Hz. What is the maximum kinetic energy of photoelectrons ejected from the metal’s surface?

A. 7 eV
B. 13 eV
C. 19 eV
D. 24 eV
E. No photoelectrons will be produced.

Correct Answer: D

Explanation:

The energy of the incident photons is

E = hf = (4.14 × 10–15 eV • s)(7.2 × 1015 Hz) = 30 eV

Since E > ø, photoelectrons will be produced, with maximum kinetic energy

Kmax = E – ø = 30 eV – 6 eV = 24 eV

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