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Heat (abbreviated Q, also called heat change) is the transfer of thermal energy between two bodies which are at different temperatures. The SI unit for heat is the joule.
The relationship between heat and energy is similar to that between work and energy. Heat flows between regions that are not in thermal equilibrium; in particular, it flows from areas of high temperature to areas of low temperature. All objects ( matter) have a certain amount of internal energy that is related to the random motion of their atoms or molecules. This internal energy is directly proportional to the temperature of the object. When two bodies of different temperature come into thermal contact, they will exchange internal energy until the temperature is equalized. The amount of energy transferred is the amount of heat exchanged. It is a common misconception to confuse heat with internal energy, but there is a difference: heat is related with the change in internal energy and the work performed by the system. Understanding this difference is a necessary part of understanding the first law of thermodynamics.
InfraredInfrared IR radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. The name means "below red" (from the Latin infra "below"), red being the color of visible light of longest wavelength. radiation is often linked to heat, since objects at room temperature or above will emit radiationIn optics, spontaneous emission is the process by which matter may lose energy, resulting in the creation of a photon. A simple model of spontaneous emission consists of an atom which may be in two electronic energy states, the ground state (1) and the ex mostly concentrated in the mid-infrared band (see black bodyIn physics a black body is an object that absorbs all light that falls onto it: no light passes through it nor is reflected. Despite the name, black bodies do radiate light. The term "black body" was introduced by Gustav Kirchhoff in 1862. The light emitt).When a body releases heat into its surroundings, Q<0. When a body absorbs heat from its surroundings, Q>0.
Total heat, heat transfer rate, and heat flux are all notated with different permutations of the letter Q. They are often confusingly switched in different contexts.
Total heat is notated as Q, and is measured in joules.
Heat transfer rate, or heat flow per unit time, is labeled
to indicate a change per unit time. In UnicodeIn computing, Unicode is the international standard whose goal is to provide the means to encode the text of every document people want to store in computers. This includes all scripts still in active use today, many scripts known only by scholars, and sy, this is Q̇ , though it may not display correctly in all browsers. It is often shown as ˙Q , .Q, Q· , or as a Q with no dot, where it is not easy to produce a dotted Q. Some form of dotted Q, such as .Q, is preferable, since undotted Q is used for total heat. It is measured in joules per second.
Heat flux is defined as amount of heat per unit time per unit cross-sectional area, and is abbreviated q, and is measured in joules per second per meter squared. It is also sometimes notated as Q
The amount of heat energy, , required to change the temperature of a material from an initial temperature, T0, to a final temperature, Tf depends on the heat capacityHeat capacity (abbreviated C or just C also called thermal capacity is the ability of matter to store heat. The heat capacity of a certain amount of matter is the quantity of heat (measured in Joules) required to raise its temperature by one kelvin. The S of that material according to the relationship:
The heat capacity is dependent on both the amount of material that is exchanging heat and its properties. The heat capacity can be broken up in several different ways. First of all, it can be represented as a product of mass and specific heat capacityThe specific heat capacity (abbreviated C also called specific heat of a substance is defined as the amount of heat energy (measured in Joules) required to raise the temperature of one kilogram of the substance by one Kelvin. The SI unit for specific heat (more commonly called specific heat):
or the number of moleThe mole (symbol: mol) is one of the seven SI base units and is commonly used in chemistry. It measures the amount of substance of a system and is defined as the amount of substance that contains as many elementary entities as there are atoms in exactly 0s and the molar heat capacity:
Both the molar and specific heat capacities only depend upon the physical properties of the substance being heated, not on any specific properties of the sample. The above definitions of heat capacity only work approximately for solids and liquids, but for gases they don't work at all most of the time. The molar heat capacity can be "patched up" if the changes of temperature occur at either a constant volume or constant pressure. Otherwise, it's generally easiest to use the first law of thermodynamics in combination with an equation relating the internal energy of the gas to its temperature.
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