Physics: Higher Level
Quantum physics — HL Theme E
- 1.
Light of frequency 7.5 × 10¹⁴ Hz is incident on a metal surface with work function 2.5 × 10⁻¹⁹ J. Calculate the maximum kinetic energy of the emitted photoelectrons. Use h = 6.63 × 10⁻³⁴ J s.
[4 marks] - 2.
Marking analysis: A learner attempts the following task: “Light of frequency 7.5 × 10¹⁴ Hz is incident on a metal surface with work function 2.5 × 10⁻¹⁹ J. Calculate the maximum kinetic energy of the emitted photoelectrons. Use h = 6.63 × 10⁻³⁴ J s.” Their response addresses only this point: “Uses the photoelectric equation hf = Φ + EKmax.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] - 3.
Explain how the photoelectric effect provides evidence for the particle nature of light, referring to the observation that emission is instantaneous and depends on frequency rather than intensity.
[4 marks] · no calculator - 4.
Marking analysis: A learner attempts the following task: “Explain how the photoelectric effect provides evidence for the particle nature of light, referring to the observation that emission is instantaneous and depends on frequency rather than intensity.” Their response addresses only this point: “States that wave theory predicts emission should depend on intensity (wave energy) and should show a time delay for energy to accumulate, neither of which is observed.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] · no calculator - 5.
Calculate the de Broglie wavelength of an electron (mass 9.11 × 10⁻³¹ kg) travelling at 2.0 × 10⁶ m s⁻¹. Use h = 6.63 × 10⁻³⁴ J s.
[3 marks] - 6.
Marking analysis: A learner attempts the following task: “Calculate the de Broglie wavelength of an electron (mass 9.11 × 10⁻³¹ kg) travelling at 2.0 × 10⁶ m s⁻¹. Use h = 6.63 × 10⁻³⁴ J s.” Their response addresses only this point: “Uses λ = h/(mv).” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] - 7.
Explain what electron diffraction experiments demonstrate about the nature of matter, and state one practical device that relies on this wave-like behaviour of electrons.
[3 marks] · no calculator - 8.
Marking analysis: A learner attempts the following task: “Explain what electron diffraction experiments demonstrate about the nature of matter, and state one practical device that relies on this wave-like behaviour of electrons.” Their response addresses only this point: “States that electron diffraction produces interference patterns, a behaviour characteristic of waves, when electrons pass through a crystal or thin film.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 9.
An electron in a hydrogen atom transitions from an energy level of −1.51 eV to a level of −3.40 eV, emitting a photon. Calculate the energy and frequency of the emitted photon. Use h = 6.63 × 10⁻³⁴ J s and 1 eV = 1.60 × 10⁻¹⁹ J.
[5 marks] - 10.
Marking analysis: A learner attempts the following task: “An electron in a hydrogen atom transitions from an energy level of −1.51 eV to a level of −3.40 eV, emitting a photon. Calculate the energy and frequency of the emitted photon. Use h = 6.63 × 10⁻³⁴ J s and 1 eV = 1.60 × 10⁻¹⁹ J.” Their response addresses only this point: “Calculates the energy released: ΔE = (−1.51) − (−3.40) = 1.89 eV.” Evaluate the response against the complete 5-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[5 marks] - 11.
Explain why atomic emission spectra consist of discrete lines rather than a continuous range of wavelengths, in terms of electron energy levels.
[3 marks] · no calculator - 12.
Marking analysis: A learner attempts the following task: “Explain why atomic emission spectra consist of discrete lines rather than a continuous range of wavelengths, in terms of electron energy levels.” Their response addresses only this point: “States that electrons in an atom can only occupy specific, discrete (quantised) energy levels.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 13.
The Heisenberg uncertainty principle can be expressed as ΔxΔp ≥ h/4π. Explain what this principle states about simultaneously measuring the position and momentum of a particle.
[3 marks] · no calculator - 14.
Marking analysis: A learner attempts the following task: “The Heisenberg uncertainty principle can be expressed as ΔxΔp ≥ h/4π. Explain what this principle states about simultaneously measuring the position and momentum of a particle.” Their response addresses only this point: “States that it is fundamentally impossible to know both the exact position and exact momentum of a particle simultaneously.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 15.
A nucleus in an excited state has energy 4.8 MeV above its ground state and decays by emitting a gamma-ray photon. Calculate the wavelength of the emitted gamma ray. Use h = 6.63 × 10⁻³⁴ J s, c = 3.00 × 10⁸ m s⁻¹ and 1 eV = 1.60 × 10⁻¹⁹ J.
[4 marks] - 16.
Marking analysis: A learner attempts the following task: “A nucleus in an excited state has energy 4.8 MeV above its ground state and decays by emitting a gamma-ray photon. Calculate the wavelength of the emitted gamma ray. Use h = 6.63 × 10⁻³⁴ J s, c = 3.00 × 10⁸ m s⁻¹ and 1 eV = 1.60 × 10⁻¹⁹ J.” Their response addresses only this point: “Converts the energy to joules: 4.8 × 10⁶ × 1.60 × 10⁻¹⁹ ≈ 7.68 × 10⁻¹³ J.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] - 17.
Distinguish between a continuous emission spectrum and a line absorption spectrum, and state the conditions under which each is produced.
[3 marks] · no calculator - 18.
Marking analysis: A learner attempts the following task: “Distinguish between a continuous emission spectrum and a line absorption spectrum, and state the conditions under which each is produced.” Their response addresses only this point: “States that a continuous spectrum contains all wavelengths across a range and is produced by a hot, dense source such as a solid, liquid, or dense gas (e.g. a filament lamp).” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 19.
In an experiment, electrons are accelerated through a potential difference of 150 V before striking a target. Calculate the de Broglie wavelength of these electrons. Use e = 1.60 × 10⁻¹⁹ C, mₑ = 9.11 × 10⁻³¹ kg and h = 6.63 × 10⁻³⁴ J s.
[5 marks] - 20.
Marking analysis: A learner attempts the following task: “In an experiment, electrons are accelerated through a potential difference of 150 V before striking a target. Calculate the de Broglie wavelength of these electrons. Use e = 1.60 × 10⁻¹⁹ C, mₑ = 9.11 × 10⁻³¹ kg and h = 6.63 × 10⁻³⁴ J s.” Their response addresses only this point: “Uses the work-energy relationship: eV = ½mv², so kinetic energy = eV.” Evaluate the response against the complete 5-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[5 marks] - 21.
Distinguish between the Bohr model and the Schrödinger (quantum mechanical) model of the atom, in terms of how each describes the position of an electron.
[3 marks] · no calculator - 22.
Marking analysis: A learner attempts the following task: “Distinguish between the Bohr model and the Schrödinger (quantum mechanical) model of the atom, in terms of how each describes the position of an electron.” Their response addresses only this point: “States that in the Bohr model, electrons orbit the nucleus in fixed, well-defined circular paths (orbits) at specific radii.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator - 23.
Calculate the momentum of a photon of wavelength 500 nm. Use h = 6.63 × 10⁻³⁴ J s.
[3 marks] - 24.
Marking analysis: A learner attempts the following task: “Calculate the momentum of a photon of wavelength 500 nm. Use h = 6.63 × 10⁻³⁴ J s.” Their response addresses only this point: “Uses p = h/λ.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] - 25.
A metal has a work function of 3.5 × 10⁻¹⁹ J. Calculate the threshold frequency for the photoelectric effect to occur at this surface. Use h = 6.63 × 10⁻³⁴ J s.
[3 marks] - 26.
Marking analysis: A learner attempts the following task: “A metal has a work function of 3.5 × 10⁻¹⁹ J. Calculate the threshold frequency for the photoelectric effect to occur at this surface. Use h = 6.63 × 10⁻³⁴ J s.” Their response addresses only this point: “States that at the threshold frequency, EKmax = 0, so hf₀ = Φ.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] - 27.
State the minimum photon energy required for pair production (in which a photon converts into an electron and a positron) to occur, in terms of the rest mass of an electron, mₑ, and calculate this minimum energy in joules. Use c = 3.00 × 10⁸ m s⁻¹ and mₑ = 9.11 × 10⁻³¹ kg.
[4 marks] - 28.
Marking analysis: A learner attempts the following task: “State the minimum photon energy required for pair production (in which a photon converts into an electron and a positron) to occur, in terms of the rest mass of an electron, mₑ, and calculate this minimum energy in joules. Use c = 3.00 × 10⁸ m s⁻¹ and mₑ = 9.11 × 10⁻³¹ kg.” Their response addresses only this point: “States that pair production requires the photon energy to be at least enough to create the rest mass energy of both the electron and the positron produced.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 marks] - 29.
Explain what is meant by quantum tunnelling, and state one physical phenomenon or application that relies on it.
[3 marks] · no calculator - 30.
Marking analysis: A learner attempts the following task: “Explain what is meant by quantum tunnelling, and state one physical phenomenon or application that relies on it.” Their response addresses only this point: “States that quantum tunnelling is the phenomenon in which a particle has a non-zero probability of passing through a potential energy barrier, even when the particle's energy is less than the height of the barrier — a situation forbidden in classical physics.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[3 marks] · no calculator