7th Class Science Heat

Heat

Synopsis

• Heat is a form of energy that can be felt by us by the sense of touch.

• Heat always flows from a hot body to a cold one, i.e., from a part that has more heat energy to the part having less heat energy.

• Heat causes certain changes in a body mainly expansion and change of state. It increases the energy of the molecules.

• Temperature is the measure of the degree of hotness or coldness of a body.

• There are different scales of temperature. Celsius, Fahrenheit, Kelvin and Reaumur are some popularly used scales.

• The average normal body temperature of human beings is \[37{{\,}^{o}}C\]or\[98.4{{\text{ }}^{o}}F.\]

• There are different types of thermometers based on their uses. Some of them are clinical thermometers, laboratory thermometers, maximum and minimum thermometers. Each thermometer has a Lower Fixed Point (the lowest temperature it can measure) and an Upper Fixed Point (the highest temperature it can measure). They are denoted as L.F.P. and U.F.P. respectively.

• When all the bodies and their surroundings have the same temperature, they are said to be in thermal equilibrium. The flow of heat takes place till thermal equilibrium is reached.

• There are three modes of transfer of heat: conduction, convection and radiation.

• The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction.

• The process of the transfer of heat in liquids or gases by the movement of molecules from the hotter to the colder part in circular currents is known as convection.

• All bodies that are hot give out heat in all directions in straight lines. Such a transfer does not require any medium and is known as radiation.

• Things that heat up slowly, cool down slowly. Those that heat up faster, cool faster.