AS physics

• Random errors


  Errors that are always present in data, and cause the measured values to be spread about the true value
• Precision, repeatability, reproducibility, resolution and accuracy

  • Characteristics of physical measurements
• Uncertainty


  Absolute, fractional and percentage uncertainties represent uncertainty in the final answer for a quantity

  
• Combining uncertainties


  1. When measurements that give rise to uncertainties are added, subtracted, multiplied, divided, or raised to powers

  2. Combinations involving trigonometric or logarithmic functions will not be required
• Individual points on a graph may or may not have associated error bars
• Students should be able to identify random and systematic errors and suggest ways to reduce or remove them
• Students should understand the link between the number of significant figures in the value of a quantity and its associated uncertainty
• Absolute, fractional and percentage uncertainties

  Represent uncertainty in the final answer for a quantity

  
• Combination of absolute and percentage uncertainties

  
• Determine the uncertainties in the gradient and intercept of a straight-line graph

  
• Individual points on the graph may or may not have associated error bars
• Students should be able to combine uncertainties in cases where the measurements that give rise to the uncertainties are added, subtracted, multiplied, divided, or raised to powers
• Random error


  One which is always present in data, and is due to readings that vary randomly, with no recognizable trend or bias
• Systematic error


  One which follows a pattern/trend, or a bias, and results in readings that systematically differ from the true mean reading
• Precision


  The smallest non-zero value that can be measured, also referred to as the resolution of that instrument
• Precision of a measurement

  The degree of exactness of a measurement, usually referred to as the uncertainty of the readings used to obtain a measurement
• Uncertainty


  The precision of a measurement due to the instrument used
• Absolute uncertainty


  The size of the range of values that the 'true' value lies
• Fractional uncertainty


  Calculated by dividing the uncertainty by the value of the data
• Percentage uncertainty


  The fractional uncertainty multiplied by 100

  
• Combining absolute and percentage uncertainties

  1. If you add or subtract values, the absolute uncertainty is the sum of the absolute uncertainties

  2. If you multiply a value by a constant, the absolute uncertainty is also multiplied by that constant

  3. If you multiply or divide values, you add the percentage uncertainties

  4. If you square or cube a value, you multiply the percentage uncertainty by 2 or 3 respectively

  
• To determine the uncertainty in the gradient of a graph, add error bars to the first and last point and draw lines through the highest and lowest values

  
• To determine the uncertainty in the y-intercept, draw lines through the highest and lowest possible intercepts
• Order of magnitude


  An estimate rounded to the nearest power of ten
• When making estimates, it is reasonable to give the figure to one or two significant figures
• The area under a curved graph can be estimated by drawing trapeziums
• Simple model of the atom

  Positively charged protons and neutral neutrons in the nucleus, with negatively charged electrons orbiting

  
• Constituents of the atom

  • Proton
  • Neutron
  • Electron
• Charge and mass of proton, neutron and electron


  Proton: +1.6x10^-19 C, 1.67x10^-27 kg

  Neutron: 0 C, 1.67x10^-27 kg

  Electron: -1.6x10^-19 C, 9.11x10^-31 kg

  
• Specific charge


  Charge to mass ratio of an atom/ion
• Specific charge calculations for proton, electron, lithium nucleus, lithium atom
• Proton number Z, nucleon number A, nuclide notation

  Z is the number of protons, A is the number of nucleons (protons + neutrons), AZ X is the notation
• Isotopes


  Atoms with the same number of protons but different numbers of neutrons
• Strong nuclear force


  Keeps the nucleus stable by overcoming electrostatic repulsion between protons, acts at very short range
• Alpha decay


  Emission of an alpha particle (2 protons, 2 neutrons) from the nucleus

  
• Beta decay


  Emission of an electron and an antineutrino from the nucleus, a neutron changes to a proton

  
• The antineutrino is crucial to conserving energy in beta decay

  
• For every particle, there is a corresponding antiparticle
• Antiparticles


  • Positron (electron)

  Antiproton (proton)

  Antineutron (neutron)

  Antineutrino (neutrino)

  
• Photon model of electromagnetic radiation

  Photons are the quanta of electromagnetic radiation, with energy E=hf=hc/λ