Thermal Properties of Matter Class 11 NCERT
Chapters learned in Class 11 forms the foundation for advanced concepts in chapters of Class 12. Hence, it is imperative for the students to have a clear understanding of basic concepts and theories and understand the formulas and derivations. In the chapter thermal properties of matter class 11, students get to learn in detail all the facts and functions related to the chapter. Our learned subject matter experts have tried to include every detail and explain in an easy way the properties of matter, physics, class 11. So, in this article, you will be able to learn the concepts of thermal expansion and superficial expansion, emissive power, absorptive power, and a lot more.
Class 11 Physics Chapter- Thermal Properties of Matter
Matter in our universe is anything that occupies space and has mass. Practically, we are surrounded by matter. Right from a chair, we sit on the bottle of water or the bag carrying books. Everything is matter. And matter has some properties by virtue of which every matter is different from the other and each of them can be identified. These properties include-
Mechanical Properties- Which tells the physical attributes of the matter like strength, elasticity, plasticity, ductility, and so on.
Chemical Properties- Which tells the chemical composition, acidity or alkalinity, Corrosive properties and so on.
Physical Properties- It tells us the conductivity, combustibility, density, etc.
Dimensional Properties- It gives information about the size and shape of the matter.
Thermal Properties- This property of matter tells how the matter will react when subjected to heat or heat fluctuations.
As we now know, thermal properties of matter are the ones due which a matter exhibits heat conductivity or it is the property that decides the nature of the matter in the presence of heat. Thus, thermal properties are exhibited by objects when heat passes through them.
By the virtue of thermal properties, different materials or objects act differently under the influence of heat. Or, these properties decide how the matter will react when they are subjected to heat fluctuations.
There are 4 major components of thermal properties. They are-
Let’s study these components in details-
Heat capacity can be defined as the amount of heat required by the body to change its temperature by 1 degree. This amount of heat is expressed in Joules or calories and the temperature fluctuations or simply the temperature is given in Celsius or Fahrenheit.
For calculation of heat capacity of an object with a particular dimension, the molar heat capacity of the object is used.
Thus, the formula is given by-
Q = m c ΔT
Q is the heat capacity in J
m is the mass in g
c is the specific heat in J.K-1
ΔT is the temperature change in °K
The shape of an object changes from its original when heat passes through it. In other words, an object expands on heating. This property of matter or object of expansion upon heating is termed as thermal expansion. On thermal expansion, the shape, volume and surface area of the objects change.
Thermal expansion is measurably large in case of gases, while it is small in case of liquids and solids.
When the change due to thermal expansion is unidimensional or taking place in one dimension, it is called linear expansion. It is given by the formula-
ΔL = αLΔT
ΔL is the change in length L
ΔT is the change in temperature
α is the coefficient of linear expansion, that varies slightly with temperature.
Not all material objects can conduct heat through their bodies. Those which can are conductors. So, such material objects let heat pass through them by the property of thermal conductivity. Among the conductors, there are ones with high conductivity, that is they conduct more heat than the ones with low heat conductivity.
The materials which do not conduct heat at all are called insulators. These objects show insulting properties.
Thermal expansion or contraction causes the body to experience some kind of stress. This is termed as thermal stress. Thermal stress some times has the potential to destroy the object, so they may turn out to be destructive in nature.
For example- you might have noticed big truck tyres get cracks on them. This is because driving on high speeds on roads causes friction between the road’s surface and the tyres that produce heat. The resultant thermal stress causes the cracks on the tyres.
1. What is Emissive Power?
Ans: The energy of thermal radiation that radiates in all directions per unit time from each of the unit areas of a surface at any temperature is called emissive power. Emissive power can be given by Stefan-Boltzmann law as-
πIb = Eb = n 2σT 4
where the total radiant intensity and hemispherical total emissive power of a blackbody into a medium with a constant index of refraction n can be calculated.
2. What is Absorptive Power?
Ans: Absorptive power is the ratio of energy absorbed in a given time period or a certain time period to the radiant energy incident on it at that same instant of time is called as absorptive power. A black body absorbs all radiations of any wavelength incident on it. Therefore, its adsorptive power is 1.