Transmission of Heat || Ways of heat transmission || CSS/PCS/PMS/IAS

Transmission of Heat || Ways of heat transmission || CSS/PCS/PMS/IAS

Transmission of Heat || Ways of heat transmission || CSS/PCS/PMS/IAS


Thermal energy flowing from warmer to colder material.

Ways of heat transmission: 

There are three ways which is use for heat transmission which are explain under below.

  1. Conduction 
  2. Convection 
  3. Radiation

1. Conduction:

If we keep one end of the iron rod in the flame, the other end soon it becomes too hot to hold. Heat gets to one end of the rod and is transmitted over the entire length. This heat transfer process is called conduction and takes place mainly in solids. Real heat mechanisms transfer differs in metals (iron, silver etc.) and non-metals (such as wood). Solids include both good and bad heat conductors. Substances such as wood, cotton, wool and glass are bad conductors (good insulators) heat. Liquids and gases are generally bad conductors. The air is very bad heat guide.

Good insulation properties of wool, cotton etc. They are mainly due to the air spaces they contain. Woolen clothes do not allow our body heat to escape and we feel warm. Sawdust is a bad guide heat. Therefore, ice plates are covered with sawdust to minimize melting. The air-conditioned rooms have double windows, consisting of two panes of glass with a thin layer of air between them, they serve as a better heat insulator than windows with single thick glass. On a cold night, two thin blankets are preferred instead of one thick blanket because the air layer between the two blankets serves as a better insulator. Ovens, geysers, etc. They have double walls with glass wool or straw between them reduce heat loss by conduction. Fridges and refrigerators have similar double walls to minimize heat gain by conduction.

When we touch the iron hammer lying in the sun, it seems much warmer than a wooden handle, because iron is a good heat conductor and conducts Heat it quickly in your hand. Wood, which is a bad heat conductor, conducts heat only from the affected surface. In winter, the stone floor is cold for bare feet, but the carpet is the same the floor is warm even though both have the same temperature. Stone, being good conductor, quickly transfers heat away from the feet. The carpet is poor conductor and transfers little heat. Therefore, the feet are cold stone, but not on the carpet. The fridge must be turned off to defrost every time a thick layer ice deposits outside and inside the freezer. Ice being poor cord, affects the cooling effect of the freezer. In this way defrosting helps efficient operation of the fridge. During the harsh winter the Eskimos live in snow huts called igloo. Snow, being a weak guide protects them from the cold. Prevents heat generation before escaping and keeps them warm.

2. Convection: 

In this process, heat is transferred from one place to another through the actual movement of liquids and gases. If we heat the liquid in the vessel from below, the liquid at the bottom warms and expands. Hot liquid rises because of its lower density, and it is replaced by cold liquid from above. In this way, "convection currents" are set and all liquid is heated to a uniform temperature. Convection currents are set in gases and air in a similar way. Heating elements in geysers and water heaters are mounted near the bottom so that the water can be heated by convection currents. Heating elements in electric ovens are mounted near the bottom to heat all enclosed air by convection. The element in the top of the oven would only heat the top layers of air, leaving the cool layers almost unchanged. The cooling unit (freezer) in the fridge is mounted on top to cool the entire interior. The air near the summit cools and falls due to increased density. Its place at the top is occupied by warm air, in this way convection currents are created, which cool the entire interior. Convection currents in the atmosphere cause winds. Sea and land winds can be explained by convection. During the day, the coast (land) heats up much faster than sea water. The air rises over the shore, and cooler air from the water takes its place, creating a sea breeze. At night the land cools faster than water, which causes a breeze of land.

3. Radiation: 

Both conduction and convection require a material medium to transfer heat from one part to another. On the other hand, radiation does not require any medium. The Earth receives radiation energy from the Sun in the form of electromagnetic waves that can pass through a vacuum. All bodies constantly emit and absorb radiation energy. If the body emits more energy than it absorbs, its temperature drops. On the other hand, if the body absorbs more energy than it emits, its temperature will rise. The body absorbs as much energy as it emits at a constant temperature. The speed at which the body emits or absorbs radiation energy depends on its temperature and the nature and surface of its surface. A rough surface is a better absorber than a smooth one, because under a microscope the rough surface has a larger surface area. Good absorbers are good emitters, and weak absorbers are poor emitters. If we pour hot coffee into two metal cups of the same size and shape at the same time, but one has a rough black surface and the other has a bright, polished surface, the coffee will cool faster in a black cup, because the rough black surface is better car cooler. In this way, coffee or tea stay hot for a longer time in the shiny, bright cup. When ice-cold water is poured into these empty cups, the water in the black cup heats up faster, because black is also a better absorber of radiation energy.

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