This is the mechanism by which heat is transferred by continual emission of electromagnetic energy (also called thermal radiation) from the surface of a body. These electromagnetic waves travel at the speed of light and are transmitted through vacuum as well as through air. When they fall on a body that is not transparent, they are absorbed, resulting in a …
This is the mechanism by which heat is transferred by motion of a fluid material. Natural convection: The flow of the fluid occurs because of the difference in density caused by thermal expansion. Forced convection: The flow of the fluid occurs because it is forced by a blower or pump. There is no simple equation for calculating the amount of …
Often, compound slabs comprising several layers of different materials are used for insulation. Consider a compound slab comprising two materials of thickness L1, L2 and thermal conductivities k1, k2 respectively. The temperatures of the outer surfaces are T1 and T2, where T2 > T1. Let the temperature at the interface be T. The compound slabs will be at steady state. …
How did the temperature gradient build up? Let us ask what happens when you attach one end of the uniform bar to the hot reservoir and the other end to the cold reservoir. For simplicity, consider that the bar is initially at the temperature of the cold reservoir, and that no heat can be lost through the surface of the …
This is the mechanism by which heat is transferred from one part of an object to another part through vibrations without net movement of material. If one part of an object is hotter than its neighboring part, the molecules or atoms in the hotter part have more energy and vibrate more vigorously than their neighbours. When they collide with their …
The heat capacity (C) of a body is the amount of heat required to raise the temperature of that body by one degree of temperature. If the heat capacity varies with temperature, we can define heat capacity as the ratio of the infinitesimal heat flow (dQ) to the infinitesimal temperature change (dT). $$C = \frac{d Q}{d T}$$ A unit of …
Liquids and solids usually expand (i.e. increase their physical dimensions) when heated. As temperature increases, atomic vibration amplitude also increases. This tends to cause an increase in bond lengths and therefore leads to thermal expansion. Anomalies: Water – Water contracts with increasing temperatures between 0°C and 4°C, before expanding at higher temperatures. Reason: – Hydrogen-bonding leads to an …