AH Physics

• Gravitational potential

  The work done in moving unit mass from infinity to that point
• The energy required to move mass between two points in a gravitational field is independent of the path taken
• Escape velocity


  The minimum velocity required to allow a mass to escape a gravitational field to infinity, where the mass achieves zero kinetic energy and maximum (zero) potential energy
• Special relativity


  • Deals with motion in inertial (non-accelerating) frames of reference
• General relativity


  • Deals with motion in non-inertial (accelerating) frames of reference
• Equivalence principle

  It is not possible to distinguish between the effects on an observer of a uniform gravitational field and of a constant acceleration
• General relativity leads to the interpretation that mass curves spacetime, and that gravity arises from the curvature of spacetime
• Light or a freely moving object follows a geodesic (the path with the shortest distance between two points) in spacetime
• The escape velocity from the event horizon of a black hole is equal to the speed of light
• From the perspective of a distant observer, time appears to be frozen at the event horizon of a black hole
• Schwarzschild radius

  The distance from the centre (singularity) of a black hole to its event horizon
• Stars are formed in interstellar clouds when gravitational forces overcome thermal pressure and cause a molecular cloud to contract until the core becomes hot enough to sustain nuclear fusion
• Stages in the proton-proton chain (p-p chain) in stellar fusion reactions which convert hydrogen to helium


  1. H + H -> H + e+ + neutrino

  2. H + H -> He + gamma

  3. He + He -> He + 2H
• Hertzsprung-Russell (H-R) diagrams are a representation of the classification of stars
• Classification of stars in Hertzsprung-Russell (H-R) diagrams

  • Main sequence
  • Giant
  • Supergiant
  • White dwarf
• Hydrogen fusion in the core of a star supplies the energy that maintains the star's outward thermal pressure to balance inward gravitational forces
• When the hydrogen in the core becomes depleted, nuclear fusion in the core ceases. The gas surrounding the core, however, will still contain hydrogen. Gravitational forces cause both the core, and the surrounding shell of hydrogen to shrink. In a star like the Sun, the hydrogen shell becomes hot enough for hydrogen fusion in the shell of the star. This leads to an increase in pressure which pushes the surface of the star outwards, causing it to cool. At this stage, the star will be in the giant or supergiant regions of a Hertzspung-Russell (H-R) diagram
• In a star like the Sun, the core shrinks and will become hot enough for the helium in the core to begin fusion
• The mass of a star determines its lifetime
• Every star ultimately becomes a white dwarf, a neutron star or a black hole. The mass of the star determines its eventual fate
• Experimental observations that cannot be explained by classical physics, but can be explained using quantum theory

  • Black-body radiation curves (ultraviolet catastrophe)
  • The formation of emission and absorption spectra
  • The photoelectric effect
• It is not possible to know the position and the momentum of a quantum particle simultaneously
• It is not possible to know the lifetime of a quantum particle and the associated energy change simultaneously
• Quantum tunnelling is a consequence of the Heisenberg uncertainty principle, in which a quantum particle can exist in a position that, according to classical physics, it has insufficient energy to occupy
• Cosmic rays originate from space and interact with Earth's atmosphere
• The solar wind is composed of charged particles in the form of plasma
• Charged particles in the Earth's magnetic field follow a helical motion
• Simple harmonic motion (SHM)


  Motion where the restoring force and acceleration are proportional to, and in the opposite direction to, the displacement from the rest position
• Derivation of relationships for SHM

  1. Velocity

  2. Kinetic energy
• Damping effects in SHM include underdamping, critical damping and overdamping
• Travelling waves

  Mathematical representation
• Stationary waves are formed by the interference of two waves, of the same frequency and amplitude, travelling in opposite directions
• Coherent waves

  Waves with a constant phase relationship
• Conditions for constructive and destructive interference in terms of coherence and phase
• A wave experiences a phase change of π when it is travelling in a less dense medium and reflects from an interface with a more dense medium
• A wave does not experience a phase change when it is travelling in a more dense medium and reflects from an interface with a less dense medium
• Interference by division of amplitude involves optical path length, geometrical path length, phase difference, and optical path difference
• Thin film interference and wedge fringes are examples of interference by division of amplitude
• A coated (bloomed) lens can be made non-reflective for a specific wavelength of light
• Interference by division of wavefront is another type of interference