Page 36 - Science Class 07
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Structure                                             In  terms  of  the  thermodynamic  system,  heat

              v It  is  smaller  in  size  than  the  laboratory    transfer  is  the  movement  of  heat  across  the
                  thermometer.                                      boundary  of  the  system  due  to  temperature
                                                                    difference  between  the  system  and  the
              v It  has  a  constric on  in  the  fine  capillary
                                                                    surroundings.  The  heat  transfer  can  also  take
                  tube.  This  constric on  prevents  the
                                                                    place  within  the  system  due  to  temperature
                  mercury from contrac ng and flowing back
                                                                    difference at various points inside the system.
                  when  it  is  removed  from  human  body
                                                                    The difference in temperature is considered to
                  (temperature of surroundings being lower).
                                                                    be ‘poten al’ that causes the flow of heat and
                  This enables the recording of the maximum
                                                                    the heat itself is called as flux.
                  temperature of the body without need for
                  haste.                                            Heat is transferred in the following ways:

              v The  mercury  thread  needs  to  be  shaken         v Conduc on          v Convec on
                  back into the bulb before the thermometer         v Radia on
                  is used again.                                    Conduc on
              It measures over a very limited range of 35°C or      The transfer of heat between two solid bodies
              94°F to 43°C or 108°F. Normal body tempera-           is  called  as  conduc on.  It  depends  on  the

              ture is 37°C or 98.4°F.                               difference in temperature of the hot and cold
                                                                    body. Example of conduc on of heat transfer is
                                                                    two  bodies  at  different  temperature  kept  in
                                                                    contact  with  each  other.  Another  example  is
               While  reading  the  temperature  on  a              hea ng one end of the metal like copper; due
               thermometer,  keep  it  horizontally  and            to  conduc on  heat  transfer,  the  other  end  of
               ensure  that  the  instrument  is  held  at  eye     the metal also gets heated.
               level and take the reading where the upper
                                                                    Convec on
               meniscus of the mercury stands.
                                                                    The transfer of heat between the solid surface
                                                                    and  the  liquid  is  called  as  convec on  heat
                                                                    transfer. Let us consider that a vessel of water
               1. What is heat?                                     being heated, in this case hea ng of water due
               2. Differen ate between heat and                      to transfer of heat from the vessel is convec on
                  temperature.                                      heat transfer.

               3. How do we measure temperature?                    Radia on
               4. Who developed kelvin scale?                       When two bodies are at different temperatures

               5. Convert 48° C in Fahrenheit.                      and  separated  by  distance,  the  heat  transfer
                                                                    between  them  is  called  as  radia on  heat

                            TRANSFER OF HEAT                        transfer.  In  case  of  the  conduc on  and
                                                                    convec on heat transfer, there is a medium to
              Heat transfer is the process of transfer of heat
                                                                    transfer  the  heat,  but  in  case  of  the  radia on
              from  high  temperature  reservoir  to  low
                                                                    heat transfer there is no medium. The radia on
              temperature reservoir.
                                                                    heat transfer occurs due to the electromagne c

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