Physics

• Conduction, convection and radiation


  • Basic everyday applications and consequences
  • Complex applications and consequences where more than one type of thermal energy transfer is significant
• Wave motion


  Vibrations in ropes and springs, experiments using water waves
• Wave


  • Wavefront
  • Wavelength
  • Frequency
  • Crest (peak)
  • Trough
  • Amplitude
  • Wave speed
• v = f λ
• Transverse wave


  Direction of vibration is at right angles to the direction of propagation
• Longitudinal wave


  Direction of vibration is parallel to the direction of propagation
• Waves can undergo


  1. Reflection at a plane surface

  2. Refraction due to a change of speed

  3. Diffraction through a narrow gap
• Use of a ripple tank to show

  1. Reflection at a plane surface

  2. Refraction due to a change in speed caused by a change in depth

  3. Diffraction due to a gap

  4. Diffraction due to an edge
• Diffraction


  • Wavelength and gap size affects diffraction through a gap
  • Wavelength affects diffraction at an edge
• Normal


  Line perpendicular to a surface
• Angle of incidence


  Angle between the incident ray and the normal
• Angle of reflection


  Angle between the reflected ray and the normal
• For reflection, the angle of incidence is equal to the angle of reflection
• Angle of refraction


  Angle between the refracted ray and the normal
• Critical angle


  Angle of incidence for which the angle of refraction is 90°
• Internal reflection


  Reflection of a wave back into the medium when it meets the boundary at an angle greater than the critical angle
• Total internal reflection


  Internal reflection of a wave when it meets the boundary at an angle greater than the critical angle
• Refractive index, n


  Ratio of the speeds of a wave in two different regions
• n = sin i / sin r
• n = 1 / sin c
• Optical fibres


  • Used in telecommunications
• Focal length


  Distance from the lens to the principal focus
• Principal axis


  Straight line passing through the centres of curvature of the lens surfaces
• Principal focus (focal point)


  Point on the principal axis where rays parallel to the axis converge or appear to diverge from
• Formation of a real image by a converging lens


  Draw and use ray diagrams
• Image characteristics


  • Enlarged/same size/diminished, upright/inverted, real/virtual
• Formation of a virtual image by a converging lens


  Draw and use ray diagrams
• Magnifying glass


  • Use of a single converging lens
• Correcting long-sightedness and short-sightedness

  • Use of converging and diverging lenses
• Visible light of a single frequency is described as monochromatic
• Regions of the electromagnetic spectrum

  • Radio waves
  • Microwaves
  • Infrared
  • Visible light
  • Ultraviolet
  • X-rays
  • Gamma rays
• All electromagnetic waves travel at the same high speed in a vacuum
• Typical uses of the different regions of the electromagnetic spectrum

  • Radio waves: radio and television transmissions, astronomy, radio frequency identification (RFID)
  • Microwaves: satellite television, mobile phones (cell phones), microwave ovens
  • Infrared: electric grills, short range communications such as remote controllers for televisions, intruder alarms, thermal imaging, optical fibres
  • Visible light: vision, photography, illumination
  • Ultraviolet: security marking, detecting fake bank notes, sterilising water
  • X-rays: medical scanning, security scanners
  • Gamma rays: sterilising food and medical equipment, detection of cancer and its treatment
• Harmful effects of excessive exposure to electromagnetic radiation

  • Microwaves: internal heating of body cells
  • Infrared: skin burns
  • Ultraviolet: damage to surface cells and eyes, leading to skin cancer and eye conditions
  • X-rays and gamma rays: mutation or damage to cells in the body
• Communication with artificial satellites is mainly by microwaves
• The speed of electromagnetic waves in a vacuum is 3.0 × 10^8 m/s and is approximately the same in air
• Important systems of communications that rely on electromagnetic radiation


  • Mobile phones (cell phones) and wireless internet use microwaves
  • Bluetooth uses radio waves
  • Optical fibres (visible light or infrared) are used for cable television and high-speed broadband
• Digital signal


  Discrete signal that can take on one of a finite number of values
• Analogue signal


  Continuous signal that can take on any value within a continuous range
• Benefits of digital signaling

  • Increased rate of transmission of data
  • Increased range due to accurate signal regeneration