SAT Subject Physics Practice Question 203: Answer and Explanation

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Question: 203

49. In an experiment designed to study the photoelectric effect, it is observed that low-intensity visible light of wavelength 550 nm produced no photoelectrons. Which of the following best describes what would occur if the intensity of this light were increased dramatically?

A. Almost immediately, photoelectrons would be produced with a kinetic energy equal to the energy of the incident photons.
B. Almost immediately, photoelectrons would be produced with a kinetic energy equal to the energy of the incident photons minus the work function of the metal.
C. After several seconds, necessary for the electrons to absorb sufficient energy from the incident energy, photoelectrons would be produced with a kinetic energy equal to the energy of the incident photons.
D. After several seconds, necessary for the electrons to absorb sufficient energy from the incident energy, photoelectrons would be produced with a kinetic energy equal to the energy of the incident photons minus the work function of the metal.
E. Nothing would happen.

Correct Answer: E

Explanation:

If the photons of the incident light have insufficient energy to liberate electrons from the metal’s surface, then simply increasing the number of these weak photons (that is, increasing the intensity of the light) will do nothing. To produce photoelectrons, each photon of the incident light must have an energy at least as great as the work function of the metal.

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