1. Three types of heat transfer are:
a. Conduction
b. Convection
c. Radiation
2. Conduction is the process by which heat energy is transmitted through collisions between neighboring atoms or molecules. Conduction occurs more readily in solids and liquids, where the particles are closer together than in gases, where particles are further apart.
3. Also unlike conduction, which relies on microscopic movement of particles to transfer heat, convection is a bulk transfer of a lot of mass at the same time. Like conduction, though, the heat transfer in convection moves from the hotter area to the colder one.
4. The specific heat capacity of a substance is the amount of heat energy required to raise the temperature of unit mass of that substance through by 1oC (or 1K).
S.I. unit is joule per kilogram per kelvin (Jkg-1K-1).
5. One calorie is defined as the amount of heat energy needed to raise the temperature of one gram of water by one degree Celsius at a pressure of one atmosphere.
(i) A calorimeter is a device used to measure the amount of heat gained or lost by a substance.
(ii) It consists of a vessel made up of metals like copper or aluminium which are good conductors of heat and electricity.
(iii) The metallic vessel is kept in an insulating jacket to prevent heat loss to the environment.
(iv) There are two holes in it. Through one hole a thermometer is inserted to measure the temperature of the contents.
(v) A stirrer is inserted through another hole for stirring the content in the vessel.
(vi) The vessel is filled with liquid which is heated by passing current through the heating element.
(vii) Using this device we can measure the heat capacity of the liquid in the container.
Short note on thermostat:
(i) A thermostat is a device which maintains the temperature of a place or an object constant.
(ii) The word thermostat is derived from two Greek words, ‘thermo’ meaning heat and ‘static’ meaning staying the same.
(iii) Thermostats are used in any device or system that gets heated or cools down - to a pre-set temperature. It turns an appliance or a circuit on or off when a particular temperature is reached.
(iv) Devices which use thermostat include building heater, central heater in a room, air conditioner, water heater, as well as kitchen equipments including oven and refrigerators.
(v) Sometimes, a thermostat functions both as the sensor and the controller of a thermal system.
Working of thermos flask:
(i) A thermos flask has double walls, which are evacuated.
(ii) It is silvered on the inside.
(iii) The vacuum between the two walls prevents heat being transferred from the inside to the outside by conduction and convection.
(iv) With very little air between the walls, there is almost no transfer of heat from the inner wall to the outer wall or vice versa.
(v) Conduction can only occur at the points where the two walls meet, at the top of the bottle and through an insulated support at the bottom.
(vi) The silvered walls reflect radiated heat back to the liquid in the bottle.
