In the photoelectric effect, Einstein's equation is E = hν − φ. Consider the following statements:
- I. φ represents the work function of the metal.
- II. Electrons will not be emitted if hν < φ.
- III. Increasing the intensity of the incident photons increases the kinetic energy of the emitted electrons.
Which of these are correct?
- AI and III only
- BI and II only
- CII and III only
- DAll
Show answer and explanation
Correct answer: (b) I and II only
Explanation
Einstein's photoelectric equation, Kₘₐₓ = hν − φ, says that a photon's energy (hν) is used first to free an electron (the work function φ) and the rest becomes the electron's kinetic energy.
- I is correct: φ is the work function, the least energy needed to remove an electron from the metal.
- II is correct: if hν < φ, no electron is emitted, however bright the light. This sets a threshold frequency.
- III is wrong: a brighter light (more intensity) means more photons, so more electrons are emitted, but each electron's kinetic energy depends only on the frequency.