Answer: threshold.
- A threshold
- B maximum
- C resonant
- D natural
Correct answer: A. threshold
Explanation: Below the threshold frequency, no photoelectrons are emitted.
In the photoelectric setup, light striking the metal plate ejects electrons that cross the evacuated tube to the collector, producing a measurable current on the ammeter.
Concept context
Photoelectric effect, de Broglie waves, Bohr's model, atomic spectra.