chapter 9

• thermal equilibrium


  happens when energy is transferred from an object with higher temperature to an object with lower temperature until both objects have the same temperature, known as thermal equilibrium

  energy transfer by heating only occurs when there is a difference in temperature

  energy in the internal store of the cooler object will increase until it has the same temperature as the surrounding/hotter object
• conduction

  energy is transferred through the passing on of vibrational motion from one particle to another

  ability to transfer energy is dependent on how quickly energy is transferred from the hotter end to the cooler end

  due to the role of electrons, materials that consists of electrons are usually good electrical or thermal conductors
• energy transfer through conduction in solid (non metals)

  energy is transferred to the rod by heating. the particles nearest to the heat source will vibrate more vigorously about their fixed positions. thus, through collisions, energy is transferred from the more energetic particle to the less energetic particles, towards the right. hence, as more energy is transferred from the left to the right, the particles on the right begins to vibrate more vigorously. the temperature of the right end of the rod increases
• energy transfer through conduction in solid (metals)

  in addition to the same process in non metals, the free electrons at the heated end gain energy from heating with particles. its small size and high speed of the electrons allow them to move easily and quickly from the hotter to cooler end and transfer energy to particles there. the free electrons moving here are collectively slower after colliding and transferring energy to the particles at this cooler end. the particles vibrate more vigorously, temperature of the end of the rod increases
• energy transfer through conduction in liquids and gases

  not as effective as particles are spaced farther apart

  probability of the particles transferring their energy through collision is lower
• energy transfer through convection

  energy is transferred through convection currents of a fluid due to difference in density

  when liquid is heated, it expands and increases in volume, volume increases so density decreases

  the warm

  the warm liquid being less dense than its surroundings will rise

  the cold liquid being denser will sink

  this difference in density results in convection currents
• energy transfer through convection in liquid

  the liquid at the bottom of the pot expands, becomes less dense and rises due to the heating via conduction through the bottom of the pot

  at the same time, the surrounding denser liquid sink to take the place of the rising liquid

  the process repeats, causing a convection current

  the circulating convection current carries warmer liquid away from the heat source and cooler liquid towards it, allowing the liquid in the pot to gain internal energy
• energy transfer through convection in air

  the air near the candle flame gains heat, becomes less dense and rises towards the top due to heating via conduction

  at the same time, the air above the opposite side of the beaker flows downwards under the t shaped card. the process repeats and causes convection currents

  the circulating convection currents carry warmer air away from the candle flame and cooler air towards it
• energy transfer through radiation

  energy is transferred by electromagnetic waves

  unlike conduction and convection, radiation does not need a medium

  rate at which an object emits or absorbs radiation is affected by surface temperature, surface area and surface colour/texture
• surface temperature of an object

  as the surface temperature increases, the rate of temperature decrease increases. as time passes. the surface temperature decreases hence the rate of temperature decrease decreases

  object of higher surface temperature will lose energy faster than the object with lower temperature such that their difference in temperature becomes smaller

  the higher the temperature of an object's surface, the lower the rate of emission of radiation
• surface area of an object


  a larger surface area will emit and absorb energy at a faster rate via radiation
• surface colour/texture of an object

  shiny, smooth or white coloured object absorbs and emits radiation at a slower rate

  matt, rough or black coloured object absorbs and emits radiation at a faster rate