9702 · 22.3
Wave-particle duality flashcards
Revision flashcards for Cambridge 9702 Wave-particle duality (syllabus 22.3). Flip, recall, then mark a real past-paper question.
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What is the core principle of wave-particle duality?
Both electromagnetic radiation (light) and matter (like electrons) can exhibit properties of both waves and particles.
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State the photoelectric equation and explain the meaning of each term.
hf = Φ + KE_max, where hf is the incident photon energy, Φ is the work function of the metal, and KE_max is the maximum kinetic energy of the emitted electron.
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What evidence supports the wave-like nature of electrons?
Electron diffraction, where electrons passing through materials with regular structures produce diffraction patterns.
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How does the de Broglie wavelength of a particle relate to its momentum?
The de Broglie wavelength (λ) is inversely proportional to the particle's momentum (p), given by λ = h/p.
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Why do atoms have discrete energy levels for their electrons?
The wave-like nature of electrons confined within the atom leads to only specific, stable energy states being allowed, a phenomenon called quantisation.
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What is a photon?
A discrete packet or 'quantum' of electromagnetic energy, with energy directly proportional to its frequency.
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Define 'work function' (Φ).
The minimum energy required to remove an electron from the surface of a specific metal.
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What is the significance of threshold frequency (f₀) in the photoelectric effect?
It's the minimum frequency of incident light required for electrons to be emitted from a metal surface. Below f₀, no electrons are emitted.
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How does light intensity affect the maximum kinetic energy of photoelectrons?
It doesn't. KE_max depends only on the *frequency* of the incident light, as one photon interacts with one electron. Intensity only increases the *number* of emitted electrons.
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What is an electronvolt (eV)?
An energy unit equal to the kinetic energy gained by an electron accelerated through a potential difference of 1 volt. 1 eV = 1.6 × 10⁻¹⁹ J.
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How is an electron's kinetic energy related to its momentum?
KE = p²/2m, where p is momentum and m is mass. This is an alternative to KE = ½mv².
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What experimental observation confirms the wave nature of electrons?
Electron diffraction. When a beam of electrons is passed through a thin crystal lattice (like graphite), it produces a diffraction pattern of concentric rings, similar to how X-rays behave.
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Why are energy levels in an atom quantised?
The electron is treated as a standing wave confined in the atom. Only wavelengths that fit into the orbit circumference (forming a stable standing wave) are allowed, which corresponds to discrete, quantised energy levels.
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An electron is accelerated by a potential difference V. What is its final kinetic energy in Joules?
The kinetic energy gained is KE = eV, where e is the elementary charge (1.6 × 10⁻¹⁹ C) and V is the potential difference in volts.