# Class 9th Physics Chapter 8th Notes

The temperature of a body is the degree of hotness or coldness of the body.

Thermometers are made to measure the temperature of a body or places.

The lower fixed point is the mark that gives the position of mercury in the thermometer when it is placed in ice.

The upper fixed point is the mark that shows the position of mercury in the thermometer when it is placed in steam from boiling water at standard pressure.

Inter-conversion between scales:

From Celsius To Kelvin Scale:

T(K)=273 + C

From Kelvin to Celsius Scale:

C =T(K)-273

From Celsius to Fahrenheit Scale:

F =1.8C+32

Heat is a form of energy and this energy is called heat as long as it is in the process of transfer from one body to another body. When a body is heated, the kinetic energy of its molecules increases, the average distances between the molecules increase.

The specific heat of a substance is defined as the amount of heat required to raise the temperature of a unit mass of that substance through one degree centigrade (1°C) or one kelvin (1K).

The heat required by unit mass of a substance at its melting point to change it from solid state to liquid state is called the latent heat of fusion.

The quantity of heat required by the unit mass of a liquid at a certain constant temperature to change its state completely from liquid into gas is called the latent heat of vaporization.

It has been observed that solids expand on heating and their expansion is nearly uniform over a wide range of temperature. Mathematically, L =L0(1+arT)

The thermal coefficient of linear expansion of a substance is defined as the fractional increase in its length per kelvin rise in temperature.

The volume of a solid changes with the change in temperature and is called as volume or cubical expansion. V =V0(1+ b rT)

The thermal coefficient of volume expansion b is defined as the fractional change in its volume per kelvin change in temperature.

There are two types of thermal volume expansion for liquids as well as for gases. Apparent volume expansion and real volume expansion.