Answer: 500 nm.
- A 250 nm
- B 400 nm
- C 620 nm
- D 500 nm
Correct answer: D. 500 nm
Explanation: At threshold, photon energy equals the work function. Thus λ<sub>0</sub> = hc/φ = 1240/2.48 nm = 500 nm.
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.