Page 148 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

Conduction

Conduction is the name given to the transmission of heat energy by contact. The heat source is in contact with
the Conductor. (metal rod). The rod is in contact with a thermometer. Due to Conduction heat is transferred from
the heated end to the free end. In general good electrical conductors are also good heat conductors and good
electrical insulators are also good heat insulators. A good heat insulator does not necessarily withstand high
temperature.
Convection
Convection is the name given to the transmission of heat energy by the up-ward flow. When heated, the fluid
(liquid/ gas) becomes less dense and because of its mobility, is displaced upwards, by a similar but colder and
more dense fluid. e.g., The domestic hot water system, The cooling system in motor cars.

Radiation
Heat is radiated or transmitted from one object to the other in space without actually being in contact, by means
of electro-magnetic waves. These waves are similar to light waves and radio waves. They can be refracted by
lenses and reflected by mirrors. This radiation is called infrared. It requires no medium to carry the radiation. (e.g)
The heat of the sun travels through the space.

Expansion of solids
A body when heated undergoes expansion. It is one of the effects of heating.
There are three types of expansion of solids:
i Linear expansion or expansion in length
ii Superficial or Areal expansion

iii Cubical or volume expansion
Coefficient of Linear Expansion
Coefficient of linear expansion is defined as the increase in length per unit length per degree rise in temperature

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CITS : WCS - Electrical - Exercise 12