CH10: Transfer of heat energy and its effects

• what is temperature?

  Temperature is the measure of how hot an

  object is.
• Heat flows from a region of higher temperature to a region of lower temperature.
• When a substance is heated, it undergoes expansion and increases in volume.

  When a substance is cooled, it undergoes contraction and decreases in volume.
• What is a bimetallic strip

  A bimetallic strip consists of two different metals that expand at different rates when heated.
• The brass expands more than the iron when heated. Hence, the heated strip bends with the brass on the outside of the curve.

  
  

  When cooled, the brass contracts more than the iron. Hence, the strip bends with the iron on the outside of the curve.
• When air in a hot air balloon is heated, its volume increases. The mass of air remains constant as the number of air particles does not change. Since the mass of air in the balloon remains constant while its volume increases, the density of air decreases. The hotter and less dense air rises, causing the hot air balloon to float.
• The movement of heat occurs through what processes?

  Conduction, convection, radiation
• What is conduction?

  Conduction is the process of heat transfer through a medium or material without any movement of the medium or material.
• What is convection?

  Convection is the transfer of heat through the movement of fluids, such as liquid or gas.
• what is radiation?

  Radiation is the transfer of heat, in the form of waves, from one place to another. It does not require a medium for transmission.
• Heat energy that is transferred by radiation may be

  absorbed or reflected.
• Factors affecting the rate of conduction

  Different materials that conduct heat at different rates.
• Factors affecting the rate of radiation

  colour, texture, surface area
• Uses of heat conductors (applications of conduction)

  Good conductors

  • are used whenever heat has to be quickly transferred

  from one place to another.

  • are found in items such as cooking utensils and

  radiators.
• Uses of heat insulators (applications of conduction)

  • used to reduce the

  amount of heat transfer.

  • Bad conductors are found in walls of buildings

  and in items such as the handles of cooking

  utensils.
• Double-glazed windows are used to reduce heat loss through the windows. A layer of air trapped between the glass panels forms an insulating layer.
• Household ventilation (applications of convection)

  • Because of its lower density than cool air, hot air rises

  and collects under the ceiling while the cooler air sinks

  • A cool room has features that let hot air out and cool

  air in.