Heat Transfer

• Heat transfer is a movement of heat from one place to another or from one object to another.
• Conduction is the heat transfer via solids
• Convection is the heat transfer via fluids (liquids and gases)
• Radiation is the heat transfer via electromagnetic waves (can be absorbed, reflected, or transmitted).
• Conduction

  • Heat transfer via solids
  • Only occurs between two objects in direct contact
  • Vibrations of the particles in solids cause conduction to occur
  • e.g. The particles in the cup of tea are vibrating very fast! As they vibrate, they nudge the slow-moving particles in the spoon. As the particles in the spoon are nudged by the fast-moving particles in the tea, they begin to vibrate faster. This increases the temperature of the spoon. Heat transfer has occurred.
• Convection

  • Heat transfer via fluids
  • Occurs in fluids - they do not have to be touching another object
  • When one part of the fluid is heated, the particles become less dense than the surrounding fluid.
  • Hot, less dense fluid rises and allows cool fluid to sink into the space freed up. However, they get heated again and rise back up. The cycle continues to form convection currents
• Radiation

  • Heat transfer via electromagnetic waves
  • Can be absorbed, reflected or transmitted
  • Due to it being transferred through electromagnetic fields, the heat can travel through the vacuum of space
  • Does not need to travel through a medium to transfer heat
  • Every object radiates heat, even if you can't feel it
  • Hotter objects radiate more heat
• Absorbing radiation

  • Different objects can absorb different amounts of radiation. it depends on the material and colour of the object
  • Dark surfaces absorb a lot of radiation. This means that they heat up much faster than light surfaces
  • Light surfaces do not absorb most radiation. Instead, they reflect most of it, which means that they stay cool
  • Clear objects, like glass, do not reflect or absorb heat radiation. Instead, they transmit the radiation. This means that radiation passes through the object.