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All 12 Flashcards — Wave–particle duality
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Question
What is a photon?
Answer
A **quantum (packet) of light energy**, E = hf.
Question
Photon energy formula?
Answer
$E = hf$ (or $E = hc/\lambda$); h = 6.63×10⁻³⁴ J s.
Question
What is the photoelectric effect?
Answer
Light ejecting **electrons** from a metal surface.
Question
The photoelectric equation?
Answer
$E_{\max} = hf - \Phi$ (max electron KE = photon energy − work function).
Question
What is the work function Φ?
Answer
The **minimum energy** needed to free an electron from the metal.
Question
What is the threshold frequency?
Answer
The lowest frequency that ejects electrons: $f_0 = \Phi/h$ (where E_max = 0).
Question
Increase the light's intensity (same frequency) — effect?
Answer
**More** electrons ejected per second; their max KE is **unchanged**.
Question
Increase the light's frequency — effect on max KE?
Answer
Max KE **increases** (E_max = hf − Φ).
Question
Why does the photoelectric effect need photons?
Answer
One electron absorbs **one photon**; a sharp threshold can't be explained by a smooth wave.
Question
Which effects show light's WAVE nature?
Answer
**Diffraction** and **interference**.
Question
Which effect shows light's PARTICLE nature?
Answer
The **photoelectric effect**.
Question
What is wave–particle duality?
Answer
Light (and matter) behaves as **both** a wave and a particle depending on the experiment.
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Topic 5.2 hub
Quantum physics (HL)
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