Heat notes for class 10 by technoedu.

                                               * Heat *

 

Heat is a form of energy that is defined as the sum of kinetic energy contained by the molecules of that object. The SI unit of heat is Joules. The AP SSC Class 10 Physical Science Chapter 1 heat discusses the various properties of heat. Heat is directly proportional to the mass of the object and the average kinetic energy. The degree of hotness and coldness of a body is known as temperature. It determines the rate of flow of heat from one body to another. The concept of heat and temperature, although related, are not alike. Let us look at a few differences between them.

Heat	Temperature
Heat is the amount of energy that flows in a body	Determines the direction of heat flow
Total potential and kinetic energy contained by molecules in an object.	The average kinetic energy of molecules in a substance.
Flows from hotter objects to colder objects	Rises when heated and lowers when cooled

Thermal Equilibrium Heat And Temperature

• If two systems, A and B, are in thermal equilibrium individually with another system C, then the systems A and B are in thermal equilibrium with each other.
• The SI unit of heat is Joule (J) and CGS unit is calorie (cal). The amount of heat required to raise the temperature of 1gram of water by 1°C is called calorie.

1 cal = 4.186 Joules

• The amount of heat required to raise the temperature of unit mass of the substance by one unit is known as the specific heat. Mathematically, it is represented as follows:

S = Q/mΔt

• Evaporation is the process of the molecules breaking free from the liquid surface at any given temperature.
• The process in which the liquid phase changes to a gaseous phase at a constant temperature and constant pressure is known as boiling.

Heat is defined as the sum of kinetic energy contained by the molecules of that object. The SI unit of heat is Joules. In c.g.s system it is measured calorie.

1calorie= 4.2joules

 

Heat depends on mass of the object and average kinetic energy of the molecules.

Heat is directly proportional to the mass of object and average kinetic energy.

 

Effects of heat are:

a. It changes the state of matter

b. It changes the temperature of an object.

c. It changes the solubility of a substance.

d. It changes the size of an object.

e. It changes the color of the body.

f. It changes the volume of the body

 

Temperature: Temperature is the degree of hotness or coldness of an object. Temperature is the thermal condition of the body that determines rate of flow of heat from one body to another. It is the average kinetic energy of the molecule.

 

Temperature scale

Centigrade scale:

Lower fixed point: 0⁰C

Upper fixed point: 100⁰C

Fahrenheit scale:

Lower fixed point: 32⁰F

Upper fixed point: 212⁰F

Kelvin scale:

Lower fixed point: 273K

Upper fixed point: 373K

 

Relation between different temperature scales

C−0100

= F−32182 = K−100100

 

Anomalous expansion of water:

Generally all substance expands on heating and contracts on cooling. But in case of water the behavior is different, when water at 0c is heated its volume decrease up to 4 and density increases. At 4c the density becomes maximum and beyond this temperature volume start to increase. Thisunusual expansion of water is called anomalous of water.

 

Graph between the volume and temperature

Graph between the density and temperature

 

Heat equation:

The amount of heat gained or lost by a body is equal to the product of the mass (m), the specific heat capacity (s) and the change in temperature (dt) of that body is called heat equation.

Q= msdt

Proof:

Let us consider the temperature of the body changes to t1 to t2 when it is heated and m be mass of the body then, change in temperature dt = t2 - t1

If Q is amount of heat supplied then, Q ……….m……..1

Q………….dt……..2

Then combining 1 and 2 we get Q=msdt………3

Where s is proportionality constant called the specific heat capacity of the material of the body which is constant for the given material and independent of the shape size and mass of the body.

 

Principle of calorimetry:

When two body of different temperature are kept in thermal contact, heat transfers takes place from the hot body to cold body and the process continues until the equilibrium (same temperature) state is maintained. This principle works on the principle of the conservation of energy.

Heat lost = Heat gained

 

 

Specific heat Capacity:

The amount of heat required to change the temperature of a body of unit mass by 1°C is known as specific heat capacity of that body.

Or s = Q/mdt

S.I unit of specific heat capacity is J/kg°C

 

Body having he more heat capacity changes the temperature slowly then the body having less heat capacity.

Specific heat capacity of water (s) = 4200 J/kg°C means 4200J of energy is needed to raise the temperature through 1⁰C

 

 

 

 

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