**Heat and Temperature | Physics grade XI :**

## Heat :

Heat is the form of energy which simulates our sense organs so that we feel hot or cold . It follows from a body of higher temperature to one of lower temperature .

Its unit is joule(J) in SI and is calorie in CGS .

1 calorie (cal) = 4.2 J

## Temperature :

The degree of hotness or coldness of body is called temperature . It determines the direction of flow of heat .

Its unit is Kelvin(K) in SI and is degree Celsius (°C) in CGS .

**Difference between heat and temperature**** :**

SN | Heat | SN | Temperature |
---|---|---|---|

1 | It is the form of energy. | 1 | It is a degree of hotness and coldness of a body. |

2 | In, SI units, its unit is joule and in CGS system its unit is calorie. | 2 | Its SI unit is Kelvin and is degree celsius in CGS system. |

3 | It is a cause . | 3 | It is a effect. |

4 | Two bodies can be in thermal equilibrium without having same amount of heat . | 4 | Two bodies can’t be in thermal equilibrium if they are at different temperatures . |

5 | It is a measure of total kinetic energy of all molecules of a body. | 5 | It is measure of average kinetic energy of all molecules of the body. |

6 | Flow of heat is independent of amount of heat energy contained in the bodies in thermal contact . | 6 | Flow of heat dependent on temperature of two bodies.If flows from a body at higher temperature t a body at lower temperature. |

## Thermal Equilibrium :

Two bodies are said to be in thermal equilibrium if they have same temperature.

## Zeroth law of thermodynamics :

If two bodies are separately in thermal equilibrium with a third body,then the first two bodies must be in thermal equilibrium with each other . This is known as Zeroth law of thermodynamics .

Consider three bodies A , B and C as shown in fig. 1 . Here A and C and also B and C are in thermal equilibrium . So A and B must be in thermal equilibrium with each other .

## Lower Fixed Point (LFP) :

The temperature at which pure ice melts under standard atmospheric pressure is called Lower Fixed Point on a chosen scale.

## Upper Fixed Point (UFP) :

The temperature at which pure water boils under standard atmospheric pressure is called Upper Fixed Point on a chosen scale .

**Temperature Scale** :

### (i) Celsius Scale :

In this scale , LFP is 0°C and UFP is 100°C . The length between LFP and UFP is divide into 100 equal parts . Each part of division represents 1°C .

### (ii) Farenheit Scale :

In this scale , LFP is 32°F and UFP is 212°F . The length between LFP and UFP is divide into 180 equal parts . Each part of division represents 1°F .

### (iii) Kelvin/Absolute Scale :

In this scale , LFP is 273K and UFP is 373K . The length between LFP and UFP is divide into 100 equal parts . Each part of division represents 1K .

### (iv) Reaumer scale :

In this scale , LFP is 0°R and UFP is 0°R . The length between LFP and UFP is divide into 80 equal parts . Each part of division represents 1°R .

## Relation between temperature scales :

**(C – 0) / (100 – 0) = (F – 32) / (212 – 32) = (K – 273) / (373 – 273)**

i.e.

### C / 100 = (F – 32) / 180 = (K – 273) / 100

Some useful links : Electrochemical Equivalent (z), Chemical Equivalent (E), their Relations and Faraday’s Constant