MCAT Physics Question 127: Answer and Explanation

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Question: 127

7. All of the following statements about the photoelectric effect are true EXCEPT:

  • A. the intensity of the light beam does not affect the photocurrent.
  • B. the kinetic energies of the emitted electrons do not depend on the light intensity.
  • C. a weak beam of light of frequency greater than the threshold frequency yields more current than an intense beam of light of frequency lower than the threshold frequency.
  • D. for light of a given frequency, the kinetic energy of emitted electrons increases as the value of the work function decreases.

Correct Answer: A

Explanation:

The greater the intensity, the greater the number of incident photons and, therefore, the greater the number of photoelectrons that will be ejected from the metal surface (provided that the frequency of the light remains above the threshold). This means a larger current. Remember that the frequency of the light (assuming it is above the threshold frequency) will determine the kinetic energy of the ejected electrons; the intensity of the light determines the number of electrons ejected per time (the current).

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