Answer: 0.5 eV.
- A 0.2 eV
- B 0.3 eV
- C 0.5 eV
- D 1.9 eV
Correct answer: C. 0.5 eV
Explanation: For the same incident frequency, the photon energy is the same. From K<sub>max</sub> = hν - φ = eV<sub>0</sub>, the difference in work functions equals e times the difference in stopping potentials. Thus the difference is 1.2 - 0.7 = 0.5 eV.
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.