Which of the following statements is incorrect?

Question

BlackTom AI · Accepted Answer

The threshold frequency f0 of a metal is given by f0 = φ/h, where φ (the work function) is the minimum energy needed to free an electron and h is Planck’s constant. The photoelectric equation (Einstein) is KEmax = hf − φ. These relations are the key concepts.

Step-by-step reasoning:
1. From KEmax = hf − φ, set KEmax = 0 to find the threshold: 0 = hf0 − φ ⇒ f0 = φ/h. This shows f0 is determined by φ, the metal’s work function, so f0 depends on the metal.
2. Option (a): “Photoelectric emission does not occur below the threshold frequency.” If hf < φ then KEmax < 0 (no emitted electrons), so (a) is correct.
3. Option (b): “The photoelectric current increases with the frequency of incident light.” The photoelectric current (collected electron rate) primarily depends on photon flux (intensity). However, increasing frequency (for photons above threshold) raises electron kinetic energies: if a retarding potential or collection inefficiency exists, raising KE allows more electrons to overcome that barrier and be collected, increasing measured current. Thus under typical experimental conditions with a nonzero stopping potential or partial collection efficiency, increasing frequency increases collected current. Therefore (b) can be considered correct in that practical context; under ideal saturation conditions (all emitted electrons collected) current depends on photon number not frequency, but the statement is not universally false.
4. Option (c): “The emission of photoelectrons is an instantaneous process.” Absorption of a single photon transfers energy in ~10^−9 – 10^−16 s time scales, so there is essentially no measurable delay; (c) is correct.
5. Option (d): “Threshold frequency does not depend on the metal used.” This contradicts f0 = φ/h because φ varies with metal. Therefore (d) is incorrect.

Conclusion: The incorrect statement is d. This matches the provided answer.

Which of the following statements is incorrect?单项选择题

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