## Introduction to Heat

Subject: Science

#### Overview

Heat is a form of energy that gives sensation of warmth. The SI unit of heat is joule. This note provides short introduction about heat and temperature scale.
##### Introduction to Heat

Heat is a form of energy that gives sensation of warmth. The SI unit of heat is joule.

In C.G.S system, the unit of heat is calorie.

1 calorie = 4.2 Joule

Heat always flow from hotter body to colder body.

#### Effect of heat:

• Heat changes the state of matter. For example: When ice is heated about 00C it turns into liquid and when water is heated above 1000C it changes into vapor.
• Heat increases the volume of substance. When any object is heated, its volume is increased.
• Heat causes thermal expansion. Because of high temperature, the body expands.
• Heat increases the temperature of body. When body is heated, temperature of the body increases.

### Temperature:

It is defined as the degree of hotness and coldness of the body. Its S.I. unit is Kelvin. The body that is hot has more temperature and that is cold has less temperature.

### Molecular theory:

According to molecular theory, heat is defined as the sum of kinetic energy present in each molecule of a body.

According to molecular theory, the average of kinetic energy of molecules of the body is called temperature.

### Fahrenheit scale:

In Fahrenheit scale, lower fixed point is 32 degree Fahrenheit and upper fixed point is 212 degree Fahrenheit. The interval between lower fixed point and upper fixed point is 180.

### Kelvin scale:

In Kelvin scale, lower fixed point is 273k and upper fixed point is 373k. The interval between lower fixed point and upper fixed point is 100. This is SI unit of temperature.

### Degree Celsius:

In degree Celsius or in centigrade scale, lower fixed point is 0 degree Celsius and upper fixed point is 100 degree Celsius. The interval between upper fixed point and lower fixed point is 100.

#### Difference between heat and temperature:

 Heat Temperature 1. It is a form of energy, which gives us sensation of warmth. 1. It is the degree of hotness and coldness of a body. 2. It is a sum of kinetic energy of all molecules present in a body. 2. It is the average of kinetic energy of all molecules present in a body. 3. It is a cause 3. It is an effect. 4. The S.I unit of heat is joule. 4. Its S.I unit is Kelvin. 5. It is measured by instrument called calorimeter. 5. It is measured by the instrument called thermometer.

#### Thermometer:

It is an instrument, which is used to measure temperature of a body.

Generally, mercury and alcohol are used as thermometric substances. Mercury can measure the temperature ranging from -39 degree Celsius to 357 degree Celsius. If we need to measure the temperature below -39 degree Celsius, we should use alcohol thermometer. Alcohol thermometer can measure the temperature ranging from -117 degree Celsius to 78 degree Celsius.

Thermometer works on the principle that solid expand on heating and contract on cooling.

Lower Fixed Point:

The temperature at which ice melts into water is called Lower Fixed Point.

Upper Fixed Point:

The temperature in which water changes into steam is called upper fixed point.

##### Things to remember
• Heat is a form of energy that gives sensation of warmth. The SI unit of heat is joule.
• In C.G.S system, the unit of heat is calorie. 1calorie = 4.2 Joule
• Heat always flow from hotter body to colder body.
• Heat changes the state of matter. For example: When ice is heated about 0̊̊̊ C it turns into liquid and when water is heated above 100̊ C it changes into vapor.
• Heat increases the volume of substance. When any object is heated, its volume is increased.
• Heat causes thermal expansion. Because of high temperature, the body expands.
• Heat increases the temperature of body. When body is heated, temperature of the body increases.
• Thermometer is an instrument, which is used to measure temperature of a body .Generally, mercury and alcohol are used as thermometric substances. Mercury can measure the temperature ranging from -39 degree Celsius to 357 degree Celsius.
• Heat is a form of energy, which gives us sensation of warmth.it is a sum of kinetic energy of all molecules present in a body, it is a cause.
• Temperature is the degree of hotness and coldness of a body.It is the average of kinetic energy of all molecules present in a body, it is an effect.
• It includes every relationship which established among the people.
• There can be more than one community in a society. Community smaller than society.
• It is a network of social relationships which cannot see or touched.
• common interests and common objectives are not necessary for society.
##### Temperature and Thermometers
We can describe heat in two ways:
Heat is the form of energy that gives us sensation of warmth.
Heat is sum of all the kinetic energy possessed by molecules of a substance.

Heat is measured in Joules (J) i.e. in SI units. In C.G.S. unit heat is measured in calorie and in F.P.S. (Foot Pound Second) heat is measured in erg.
The relation between them is 1 calorie = 4.2 J = 41840000 erg

There are two basic factors that affect heat energy of a substance: (This can be deduced from 2nd definition of heat)
1. The number of molecules that a substance possesses.
2. The average kinetic energy of the molecules of that substance.

Here, mass of the waater (m) =100g

= $\frac{100}{1000}$kg

= 0.1 kg

Initial temperature (t1) = 5°c

finaltemperature (t2) = 90°c

∴ Rise in temperature (dt) = t2-t1

= 90-5

=85°c

sp. heat capacity of water (s) =4200 jkg-1°c-1

∴ Amount of heat suppied(Q) =?

We have,

Q = msdt

= 0.01 x4200 x85

=38700 J

Here, Heat supplied (Q) =50 kj

= 50× 1000j (∴1kj = 1000j)

=50000J

Mass of water (m) = 10 kg

Sp. heat capacity of water (s) =4200jkg-1°c-1.

Rise in temperature (dt) = ?

We have, Q = msdt

or,dt =$\frac{Q}{ms}$

= $\frac{50000}{10×4200}$

= 1.19°C

Therefore , the rise in teemperature of water is 1.19°C.