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 are the main thermal properties of matter?
Thermal properties of matter are characteristics that describe how a substance responds to the application of heat. The primary thermal properties include heat capacity, thermal expansion, thermal conductivity, and latent heat. These properties collectively determine how a material stores thermal energy, changes its size with temperature, transfers heat, and changes its physical state.
2. What is the difference between heat capacity and specific heat capacity?
The main difference lies in their dependency on mass. Heat capacity is the amount of heat required to raise the temperature of an entire object by 1°C. It is an extensive property, meaning it depends on the object's mass and material. In contrast, specific heat capacity is the heat required to raise the temperature of 1 kg of a substance by 1°C. It is an intensive property, which is a characteristic of the material itself, not its size.
3. What is thermal expansion and what are its types?
Thermal expansion is the tendency of matter to change its shape, area, and volume in response to a change in temperature. When a substance is heated, its particles gain kinetic energy, move more vigorously, and increase the average separation between them. The three main types are:
- Linear Expansion: The change in a material's length.
- Area (Superficial) Expansion: The change in a material's surface area.
- Volume (Cubical) Expansion: The change in a material's overall volume.
4. What are the three modes of heat transfer?
Heat energy can be transferred from a hotter region to a colder region through three distinct modes:
- Conduction: The transfer of heat through direct molecular collisions without any net movement of the medium itself. It is the primary mode of heat transfer in solids.
- Convection: The transfer of heat through the bulk movement of fluids (liquids or gases). Hotter, less dense fluid rises, and cooler, denser fluid sinks, creating convection currents.
- Radiation: The transfer of heat through electromagnetic waves, which can travel through a vacuum and does not require a medium. An example is the warmth from the sun.
5. What is latent heat and how is it calculated?
Latent heat is the amount of heat energy absorbed or released by a substance during a change of state (e.g., from solid to liquid or liquid to gas) at a constant temperature. This energy is used to break or form intermolecular bonds. The total heat (Q) required to change the state of a substance of mass (m) is calculated using the formula Q = m × L, where L is the specific latent heat of the substance for that particular phase transition.
6. Why do railway tracks have gaps between them?
Railway tracks have small gaps left between successive rails to accommodate for linear thermal expansion. In the summer heat, the metal rails expand in length. Without these expansion gaps, the immense force from the expanding rails would cause them to push against each other, leading to bending and buckling. This could make the track unsafe and potentially cause derailments.
7. How does the anomalous expansion of water benefit aquatic life?
Water exhibits anomalous expansion, meaning it is densest at 4°C and becomes less dense as it cools further to 0°C. This unique property is crucial for the survival of aquatic life in cold climates. As a lake or river cools, the colder, less dense water stays at the surface and freezes, forming an insulating layer of ice. This ice layer prevents the water below from freezing, allowing fish and other organisms to survive in the liquid water underneath throughout the winter.
8. What is the fundamental difference between conduction, convection, and radiation?
The fundamental differences relate to the mechanism of transfer and the need for a medium. Conduction transfers heat through direct particle-to-particle vibration and requires a medium. Convection transfers heat through the physical movement of a heated fluid (liquid or gas) and also requires a medium. Radiation, however, transfers heat via electromagnetic waves and is unique because it does not require any medium, allowing it to travel through the vacuum of space.
9. What is thermal conductivity and how does it differ in conductors and insulators?
Thermal conductivity is a measure of a material's ability to transfer heat. Materials with high thermal conductivity, such as metals, are called conductors because they allow heat to pass through them quickly. In contrast, materials with low thermal conductivity, like wood, glass, or air, are known as insulators because they significantly slow down the transfer of heat.
10. Why is a perfectly black body considered a perfect emitter of radiation?
A perfectly black body is an ideal object that absorbs all radiation that falls on it. According to Kirchhoff's Law of Thermal Radiation, for any object in thermal equilibrium, its ability to emit radiation (emissivity) is equal to its ability to absorb radiation (absorptivity). Since a black body is defined as a perfect absorber with an absorptivity of 1, it must also be a perfect emitter with an emissivity of 1, radiating the maximum possible thermal energy for its given temperature.
