**Thermal expansion and calorimetry**

**Heat:-**it is a form of energy, which produce in us the sensation of warmth

**Temperature:-**The degree of hotness or coldness of a body is called temperature

**Thermometer:-**It is a device used to measure the temperature of a body

**Scales of temperature:-**there are four scales of temperature. Given below is scales of temp with lower and upper fixed point

**Temperature scales Lower fixed point (Melting point office)**

**Upper fixed point (Boiling point of water)**

1. Celsius 0

^{0 }C 100

^{0 }C

2. Fahrenheit 32

^{0 }F 212

^{0 }F

3. Reamur 0

^{0 }R 80

^{0 }R

4. Kelvin 273 K 373 K

**Relation between the various temperature scales**

If C,F, R and K are temperature of a body on Celsius, Fahrenheit , Reumer and Kelvin scale, then

**C/5 = F-32/9 = R/4 = K -273 /5**

**Thermal expansion:-**all solid expands on heating.

There are three types of expansion.

**(1) Liner expansion:-**When a solid rod of initial length ‘l’ is heated through a temperature then its new length l

where α is called coefficient of liner expansion.

**(2) Superficial expansion:-**when a solid of initial surface area A is heated through temperature then its new Area is

where β is coefficient of superficial expansion

**(3) Cubical expansion:-**when a solid of initial volume V is heated through a temperature then its new volume is

where ϒ is the coefficient of cubical expansion.

Where ϒr =Coefficient of real expansion of a liquid

ϒa = Coefficient of apparent expansion of liquid

ϒg = Coefficient of cubical expansion of the vessel

**Thermal capacity**= It is the amount of heat required to raise its temperature through one degree

**Water equivalent :-**It is the mass of water which absorbs or emits the same amount of heat as is done by the body for the same rise or fall in temperature. It is represented by W = mc

**Specific heat :-**It is the amount of heat required to raise the temperature of unit mass of substance through unit degree Celsius

**Latent heat :-**It is define as the quantity of heat required to change the unit mass of the substance from its one state completely to another state at constant temperature

**Calorimeter :-**Device used for measuring heat

**Principle of calorimetry :-**Heat loss by hot body = Heat gain by cold body

**Transfer of heat :-**there are three modes by which heat transfer takes place

**(1) Conduction:-**It is the process by which heat is transmitted from one point to another through a substance in the direction of fall of temperature without the actual motion of the particles of the substance. When two opposite faces of a slab, each of cross section A and separated by a distance d are maintained at temperature T

_{1}and T

_{2}(T

_{1}> T

_{2}), then amount of heat that flows in time t

Where K is coefficient of thermal conductivity of the mater

**Coefficient of thermal conductivity:-**It may be defined as the quantity of heat energy that flows in unit time between the opposite faces of a cube of unit side, the faces being kept at one degree difference of temperature.

S.I unit of coefficient of thermal conductivity :

**(2) Convection:-**It is the process by which heat is transmitted through a substance from one point to another due to the bodily motion of the heated particles of the substance.

**(3) Radiation:-**It is the process by which heat is transmitted from one place to another without heating the intervening medium

**Newton’s laws of cooling:-**It states that the rate of loss of heat or rate of cooling of a body is directly proportional to the temperature difference between the body and the surrounding, provided the temperature difference is small

Mathematically

**Perfect black body:-**It is a body which absorbs heat radiations of all the wavelengths, which fall on it and emits the full radiation spectrum on being heated.

**Stefan’s law:-**It states that the total amount of heat energy radiated per unit area of a perfect black body is directly proportional to the fourth power of the absolute temperature of the substance of the body

Mathematically

**Wein’s displacement law:-**According to this law, the wavelength λm of maximum intensity of emission of black body radiation is inversely proportional to absolute temperature (T) of black body.

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