Physics - Heat & Light

• Effects of Heat


  • Gaps in roads allow space for roads to expand on a hot day
  • Gaps in railway tracks allow space for railway tracks to expand on a hot day
  • Bridge rollers allow bridges to move and expand smoothly during a hot day
  • Electric cables are longer to allow cables to contract during cold nights
• Changes in Solid, Liquid, Gas

  • Expands when heated
  • Contracts when cooled
  • Particles gain heat energy
• Uses of Bimetallic strip (2 metal strip)

  • Fire alarm (strip heated to connect circuit)
  • Clothes iron (strip heated to break circuit)
• Conduction

  • Travels in solid
  • Transfers through direct contact based on condition of particles
  • Insulated by using different materials with low conductivity
• Conduction used in

  • Boiling kettle
  • Melting chocolate/ice cube
• Convection


  • Travels in liquid/gas
  • Hot fluid goes up due to lower density whilst cold fluid goes down
• Convection used in

  • Hot-air balloon
  • Fridge
  • Air-con
• Radiation


  • Travels in vacuum
  • Transfers in the absence of medium through infrared radiation
  • Insulated by reflection of heat
• Radiation used in

  • Microwave
  • Solar panels
• Light


  • A form of energy that can be seen
  • Travels in transverse wave
  • Part of the electromagnetic spectrum
• Properties of Light


  • Travels in a straight line (linear propagation)
  • Travels in all directions
  • Travels faster than sound
• Types of Objects

  • Luminous Body (produces its own light)
  • Non-Luminous Body (does not produce own light)
  • Transparent (allows all light to pass through)
  • Translucent (allows some light to pass through)
  • Opaque (allows no light to pass through)
• Shadows


  Dark region that is formed when an object is blocking the light source
• Law of Reflection


  • The angle of incidence is equal to the angle of reflection
  • The incident ray, normal and reflected ray all lie on the same plane
• Types of Reflection


  • Regular reflection (smooth surface)
  • Diffuse reflection (rough surface)
• Reflected Ray


  Light ray that is reflected from surface
• Reflected Angle


  Angle between reflected ray and normal
• Incident Ray


  Light ray that strikes a surface
• Incident Angle


  Angle between incident ray and normal
• Properties Of Mirror Image

  • Same size, shape, colour, side up, distance between object
  • Virtual image (image that cannot be projected or formed on screen)
  • Laterally inverted (reflected backward [left & right flipped])
• Refraction


  • The bending of light due to change in speed
  • Light bends when it hits transparent surface with different optical density
  • When light travels from a less dense to a more dense medium (it slows down & bends closer to normal)
  • When light travels from a more dense to a less dense medium (it speeds up & bends away from normal)
  • Incident ray (parallel to emergent ray)
• Colours


  • ROYGBIV
  • White light consists of different wavelengths, speed, & refractive purposes
  • Primary colours- red, blue, green
  • Secondary colours- yellow, magenta, cyan
  • Splitting of light: refraction & dispersion
• Coloured filters


  Allow certain colours to transmit and absorb other colours
• Light: transverse wave, doesn't need matter, 3 X 10*8 m/s
• Sound: longitudinal, needs matter, air 330m/s liquid 1500m/s solid 6000m/s