E.2 Quantum physicsIB Physics HL: Flashcards

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What does the photoelectric effect provide evidence for?

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What does the photoelectric effect provide evidence for?: The particle (photon) nature of light.
What is the threshold frequency?: The minimum frequency of light that releases photoelectrons from a given metal.
Define work function Φ.: The minimum energy needed to remove an electron from the surface of the metal.
Einstein's photoelectric equation?: Emax = hf − Φ
What happens to Emax if intensity is doubled at fixed frequency?: Nothing; only the number of photoelectrons per second (current) doubles.
Why is emission instantaneous even at low intensity?: One photon gives all its energy to one electron at once, so no energy needs to build up.
On a graph of Emax against f, what are the gradient and the frequency intercept?: Gradient = h; intercept = threshold frequency f₀.
De Broglie wavelength of a particle?: λ = h/p
Momentum of a particle of mass m with kinetic energy E?: p = √(2mE)
What is evidence for the wave nature of matter?: Diffraction of particles, e.g. electrons diffracting through thin graphite.
Why do electron diffraction rings shrink when the accelerating voltage is increased?: Momentum increases so λ decreases, giving smaller diffraction angles.
What is wave–particle duality?: Light and matter both show wave and particle properties, depending on the experiment.
What happens to a photon in Compton scattering?: It collides with an electron, loses energy and its wavelength increases.
Compton shift formula?: Δλ = (h/(mₑc))(1 − cos θ)
At what angle is the Compton shift largest?: θ = 180° (back-scattering), where Δλ = 2h/(mₑc).