Heat Transfer

•    There are three methods of transfer of heat namely conduction, convection and radiation.
•    Conduction is the process of transfer of heat from the hot end to the cold end, from particle to particle of the medium.
•    Convection is the process of heat transfer by actual movement of the medium particles.
•    Radiation is the process of heat transfer in which heat directly passes from the hot body to cold body without affecting the medium.
•    Conduction and convection requires a medium while radiation does not require a medium.
•    The transfer of heat in solids is mainly due to conduction, while in liquids and gases heat transfer is mainly due to convection.
•    In conduction, the molecules of the solid at the hot end absorb the heat energy. They begin to vibrate more rapidly and collide with their neighbouring molecules. During collision, they pass heat to the neighbours without moving themselves from the mean position.
•    In convection, the molecules of the solid of liquid or gas absorb heat from the source. They themselves move upward and the molecules from the upper part move downward to take their place.
•    In radiation, heat is transferred directly from hot body to cold body without affecting the medium.
•    The substances which allow heat to pass through them easily are known as good conductors of heat. Metals are good conductors of heat.

                                                

•    The substances which do not allow heat to pass through them easily are known as bad conductors of heat.
•    Liquids and gases are good conductors of heat. Solids are not heated by convection. In vacuum transfer of heat takes place due to radiation only.
•    Dull and black surfaces absorb more radiation while the white and shiny surface reflects more radiation.
•    Thermo flask is a device in which transfer of heat by conduction, convection and radiation is reduced to a minimum, so it keeps the contents at the same temperature for a long time.

 

 

To Access the full content, Please Purchase

  • Q1

    Why do we wear woollen clothes in winters?

    Marks:2
    Answer:

    Woollen clothes have a large amount of trapped air. Air prevents the heat of a body to flow outwards because it is a bad conductor of heat. Therefore, we feel warm, as our body does not loose heat to the surroundings.

    View Answer
  • Q2

    What is thermal radiation?

    Marks:1
    Answer:

    The heat energy transferred from a hot to a cold object by the process of radiation is known as radiant heat or thermal radiation.

    View Answer
  • Q3

    What is radiation?

    Marks:1
    Answer:

    The process of transfer of heat in which heat is transferred from a hot body to a cold body with or without any intervening media is called radiation.

    View Answer
  • Q4

    What is convection?

    Marks:1
    Answer:

    The mode of transfer of heat in which the particles move up towards the source of heat and then, they move away from it, is called convection.

    View Answer
  • Q5

    What is conduction?

    Marks:1
    Answer:

    The process of transfer of heat from hotter end to colder end, from one particle to the next nearest particle is called conduction.

    View Answer