What is the physical meaning of the 'Work Function' of a metal in the context of the photoelectric effect?
A. The maximum kinetic energy of an emitted electron.
B. The electrical resistance of the metal when light shines on it.
C. The total energy of an incident photon.
D. The minimum energy required to eject an electron from the metal surface.
Answer: Option D
Solution (By JKSSB Mock Tests)
In Einstein's photoelectric theory, electrons are bound to the metal lattice. The 'work function' (often denoted by Phi or W) is defined strictly as the absolute minimum thermodynamic work (energy) needed to overcome these binding forces and remove an electron from the surface into a vacuum. If incident photon energy (hf) is less than the work function, absolutely no emission occurs.
Explanation:
KE = p²/(2m) = (10)²/(2×2) = 100/4 = 25 J. Wait, recalculate: 100/4 = 25 J. Option B is correct. KE = p²/2m relates momentum and kinetic energy. Memory tip: When given momentum, use KE = p²/2m instead of finding velocity first. Efficient calculation method for competitive exam time constraints.
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