Heat effects and its measurement scales

 Heat is a form of energy which produces a sensation in our body by way of which we make out whether a body is cold, warm or hot.

Hence it has the ability to do work. For example, the steam engine pulls a train converting heat into mechanical energy.

Heat can also be converted to other forms of energy. For example, the heat in a fire cracker produces both sound and light.



Effects of Heat energy

a)    Heat energy brings about change in temperature conversely, if a hot body gives out heat energy, its temperature falls.

b)    Heat energy brings about change in dimensions when a material body is heated, its length, area and volume increases.

c)     Heat energy brings about change in state. When heat supplied to the solid, at a particular constant temperature it changes into the liquid state. Similarly liquid changes into gaseous state. During the change of state, the temperature of the body remains constant.

d)    Heat energy affects the living things.

e)    Heat energy brings about chemical change when calcium carbonate is heated strongly; it changes into calcium oxide and carbon dioxide.

Sources of Heat Energy

Sun is the Earth’s main source of heat energy. Other sources of heat include burning of fuels, for instance, wood, coal, kerosene and liquefied petroleum gas(LPG), rubbing of two surfaces against each other, or from electricity. Heat always flows from a body of higher temperature to the body at lower temperature.

A body which is losing heat is feeling the other body to be cold, and a body which is gaining heat is feeling the other body to be hot.

S.I unit of heat energy is joule (J). Another commonly used unit of heat is calorie (cal). One calorie is the quantity of heat energy required to raise the temperature of 1g of water through 10C.

1 cal = 4.2 J         1 kcal = 1000 calories

Thermometry

Thermometry is the branch of heat dealing with the measurement of temperature. The degree of hotness or coldness of the body is called temperature. S.I unit of temperature is Kelvin (k). Other unit of temperature is degree Celsius (0C) and degree Fahrenheit (0F).

The device used for measuring the temperature of a substance is called Thermometer.

“Thermo” is a Latin word which means heat and matter means a measuring device. Thermometer works on the principle that matter expands when heated and contract when cooled.

There are different thermometric substances like mercury, alcohol etc., used in thermometers for different range of temperatures to be measured. Mercury is used in thermometers as thermometric substance because of the following advantages.

a)    It expands evenly as the temperature rises.

b)    It is a good conductor of heat.

c)     Its density is higher.

d)    It is very sensitive in expansion.

e)    It does not stick on the wall of a glass tube.

f)      It has very low freezing point and a very high boiling point.

The calibration of thermometer involves fixing of two points on it one lower fixed point (L.F.P) and other upper fixed point (U.F.P).

The melting point of pure ice at normal atmospheric pressure is taken as lower fixed point (L.F.P). The boiling point of pure water at normal atmospheric pressure is taken as upper fixed point (U.F.P).

The constant temperature at which, the solid substance changes into liquid is called its melting point. The constant temperature at which, a liquid changes into gaseous state is called boiling point.




Scales of Temperature

Celsius scale (or) centigrade scale

It was devised by Anders Celsius in 1710. On this scale, ice point (L.F.P is taken as 00C and steam point is taken as 1000C. The fundamental interval (interval between L.F.P and U.F.P) is divided into 100 equal parts (divisions). Each division corresponds to a difference of temperature of 10C.

Fahrenheit scale

It was devised by Fahrenheit in 1717. Here ice point (L.F.P) is taken as 320F and steam point (U.F.P) is taken as 2120F. The fundamental interval is divided into 180 equal parts. Each part corresponds to a difference of temperature of 10F.

Kelvin scale

It was given by Lord Kelvin (1824-1907). Here, ice point (L.F.P) is taken as 273 K and steam point. Steam point (U.F.P) is taken as 373 K. The fundamental interval is divided into 100 equal parts. Each division corresponds to 1 K.

Thermal Expansion

The increase in size of an object on heating is called thermal expansion. Thermal expansion takes place in all bodies and in all three states of matter.

Expansion of solids

A solid has a definite shape, so it shows all three types of expansions i.e., on heating solids show an increase in length (linear expansion), in area (superficial expansion) and in volume (cubical expansion).


Read more: Some oldtechniques to detect lamp defects and troubleshooting ideas. 


Heat effects and its measurement scales  Heat effects and its measurement scales Reviewed by knowledge people creators on October 30, 2021 Rating: 5
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