# Quantum Mechanics - Objectives

Content
• Interference
• Diffraction
• Two-source interference
• Energy of a photon
• Photoelectric emission
• Energy levels and photon emission
• Wave-particle duality

Learning Outcomes

Candidates should be able to:

• describe the photoelectric effect.
• Path difference. Coherence.
• Interference and diffraction using a laser as a source of monochromatic light
• Young’s double-slit experiment: the use of two coherent sources or the use of a single source with double slits to produce an interference pattern.
• Fringe spacing, w = λD/s
• Production of interference pattern using white light.
• Students are expected to show awareness of safety issues associated with using lasers.
• Students will not be required to describe how a laser works.
• Students will be expected to describe and explain interference produced with sound and electromagnetic waves.
• Appreciation of how knowledge and understanding of nature of electromagnetic radiation has changed over time
• Appearance of the diffraction pattern from a single slit using monochromatic and white light.
• Qualitative treatment of the variation of the width of the central diffraction maximum with wavelength and slit width. The graph of intensity against angular separation is not required.
• Plane transmission diffraction grating at normal incidence.
• Derivation of dsinθ = nλ
• Use of the spectrometer will not be tested.
• Applications of diffraction gratings.
• show an appreciation of the particulate nature of electromagnetic radiation, i.e. a photon model.
• recall and use E = hf.
• explain why the maximum kinetic energy of photoelectrons is independent of intensity, and why the photoelectric current is proportional to intensity of the incident radiation.
• explain photoelectric phenomena in terms of photon energy and work function energy.
• understand and explain in terms of photons: Work function φ, threshold frequency f0, stopping potential
• recall, use and explain the significance of hf = φ + ½m(vmax)2 , where φ is the work function energy of the surface. the stopping potential experiment is not required.
• define, understand and use the electronvolt (eV) as a unit of energy.
• Ionisation and excitation; understanding of ionization and excitation in the fluorescent tube.
• Line spectra (e.g. of atomic hydrogen) as evidence of transitions between discrete energy levels in atoms; hf = E1 - E2
• electron diffraction suggests the wave nature of particles and the photoelectric effect suggests the particle nature of electromagnetic waves; details of particular methods of particle diffraction are not expected.
• recall and use the de Broglie equation λ = h/mv, where mv is the momentum.
• explain how and why the amount of diffraction changes when the momentum of the particle is changed.
• appreciate how the knowledge and understanding of the nature of matter has changed over time
• appreciate that such changes need to be evaluated through peer review and validated by the scientific community
• Required practical: Investigation of interference effects to include the Young’s slit experiment and interference by a diffraction grating.