Thermal Properties of Matter Class 11 NCERT
Chapters learned in Class 11 form 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
Introduction
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 matters. 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.
What are Thermal Properties of Matter?
As we now know, the thermal properties of matter are the ones due to 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-
Heat capacity
Thermal Expansion
Thermal conductivity
Thermal stress
Let’s study these components in detail.
Heat Capacity
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.
How to Calculate the Heat Capacity
For the calculation of the heat capacity of an object with a particular dimension, the specific heat capacity of the object is used.
Thus, the formula is given by-
Q = m c ΔT
where,
Q is the heat capacity in J
m is the mass in g
c is the specific heat in J/kg.K
ΔT is the temperature change in °K
Thermal Expansion
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 thermal expansion. On thermal expansion, the shape, volume, and surface area of the objects change.
Thermal expansion is measurably large in the case of gases, while it is small in the case of liquids and solids.
Linear Expansion
When the change due to thermal expansion is unidimensional or takes place in one dimension, it is called linear expansion. It is given by the formula-
ΔL = αLΔT
Where,
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.
Modes Of Heat Transfer
Heat can be transferred from one system to another or from one part of a system to another in three distinct modes.
Conduction - Here the transfer of heat happens from one part of a body to its adjacent part because of the difference in their overall temperature.
For example, when we heat one end of a rod in flames, the other end of the rod also ends up turning hot soon.
Convection - Here the transfer of heat happens because of motion in the matter and can be possible only in the case of fluids.
For example, when the human heart pumps and circulates blood in the human body, the heat generated by the cells in the body is transferred to the blood flowing through the blood vessels
Radiation - Here the transfer of heat happens through electromagnetic waves.
For example, the earth gets heated up by the direct rays of the sun falling on it.
Thermal Conductivity
Not all material objects can conduct heat through their bodies. Those who can are called 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.
Thermal Stress
Thermal expansion or contraction causes the body to experience some kind of stress. This is termed thermal stress. Thermal stress sometimes has the potential to destroy the object, so it 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 at high speeds on roads causes friction between the road’s surface and the tyres that produce heat. The resultant thermal stress causes cracks on the tyres.
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FAQs on Thermal Properties of Matter
1. What is Emissive Power?
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?
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 absorptive power. A black body absorbs all radiations of any wavelength incident on it. Therefore, its adsorptive power is 1.
3. What is the relation between Heat Capacity and Specific Heat Capacity?
Heat Capacity measures the amount of heat necessary to raise the temperature of an object or a system by one degree Celsius. Specific Heat Capacity is an intensive property that describes how much heat must be added to a particular unit mass of an object to raise its temperature by one-degree celsius.
s= \[\frac {Q} {m\Delta T}\]
Where,
s = Specific Heat Capacity
Q = amount of heat given to an object
m = mass of the object
T = change in temperature
4. What is Latent Heat?
When a certain amount of heat energy is transferred between a substance and its surroundings, it changes its state from one form to another at a constant temperature. This amount of heat transferred during the change of state of an object per unit mass is called Latent Heat.
If the mass m of a substance changes from one state to another, then the quantity of heat required is
Q = m * L
from which we can derive
L = Q / m
Where,
Q = Quantity of heat required
m = mass of an object
L = Latent Heat
5. What are the different temperatures at which a body changes its physical state from one state to another?
MELTING POINT - The temperature at which a solid form melts into a liquid form.
FREEZING POINT - The temperature at which a liquid freezes to a solid form.
BOILING POINT - The temperature at which a liquid changes its form to the gaseous state.
SUBLIMATION - The process where a substance solid changes directly into vapour.
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