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A photocell circuit has its cathode illuminated by monochromatic light. If the intensity of light is kept constant and only the frequency of the incident light is increased, which of the following statements is correct?

1. The photoelectric current in the circuit increases
2. The photoelectric current in the circuit decreases
3. The maximum kinetic energy of the emitted photoelectrons increases
4. The photoelectric current can be reduced to zero by reversing the polarity of the terminals

Correct answer: The maximum kinetic energy of the emitted photoelectrons increases

Solution

According to Einstein's photoelectric equation, maximum kinetic energy KE_max = hf - phi (work function). Increasing frequency f at constant intensity increases KE_max directly. The number of photons per second decreases (since each photon is more energetic), so photocurrent actually decreases slightly, but the definitive and always-true statement is that KE_max increases. Option (c) is unambiguously correct.

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