My Notes
It is hotter for the same distance over the top of fire than it is inside of it, mainly because
(1) Air conducts heat upwards
(2) Heat is radiated upwards
(3) Convection takes more heat upwards
(4) Convection, conduction and radiation all contribute significantly transferring heat upwards
Air is a bad conductor of heat or partly conducts heat. Still, a vacuum is to be placed between the walls of the thermos flask because:
| 1. | it is difficult to fill the air between the walls of the thermos flask. |
| 2. | due to more pressure of air, the thermos can get cracks. |
| 3. | by convection, heat can flow through the air. |
| 4. | on filling the air, there is no advantage. |
While measuring the thermal conductivity of a liquid, we keep the upper part hot and the lower part cool, so that:
| 1. | convection may be stopped |
| 2. | radiation may be stopped |
| 3. | heat conduction is easier downwards |
| 4. | it is easier and more convenient to do so |
Mode of transmission of heat, in which heat is carried by the moving particles, is
(1) Radiation
(2) Conduction
(3) Convection
(4) Wave motion
In heat transfer, which method is based on gravitation ?
(1) Natural convection
(2) Conduction
(3) Radiation
(4) Stirring of liquids
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