Class11th science physics( Thermal Properties of Matter)

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By definition, matter or material is anything that has mass and occupies space. Everything we see around us is matter. For example, a water bottle is made up of plastic or any metal, both of which are examples of matter.
The matter has properties or characteristics, by which they can be identified. The major properties of materials can be categorized under:
  • Mechanical properties of materials
  • Chemical properties of materials
  • Physical properties of materials
  • Dimensional properties of materials
  • Classification Of Material Property

What are Thermal Properties of Matter?

Thermal properties are those properties of a material which is related to its conductivity of heat. In other words, these are the properties which are exhibited by a material when heat is passed through it. Thermal properties come under the broader topic of physical properties of materials.
Thermal properties of a material decide how it reacts when it is subjected to heat fluctuation (excessive heat or very low heat, for example). The major components of thermal properties are:
  • Heat capacity
  • Thermal Expansion
  • Thermal conductivity
  • Thermal stress
  • Heat Capacity
Heat capacity of a material can be defined as the amount of heat required to change the temperature of the material by one degree. The amount of heat is generally expressed in joules or calories and the temperature in Celsius or Kelvin. In order to calculate the heat capacity of materials with a given dimension, Molar heat capacity or specific heat capacity is used.
Heat capacity can be measured by the following formula:
Q=mcΘ
is the amount of heat transferred, is the change in temperature.

What is Thermal Expansion?

When heat is passed through a material, its shape changes. Generally, a material expands when heated. This property of a material is called Thermal Expansion. There can be a change in the area, volume and shape of the material. For example, railway tracks often expand and as a result, get misshapen due to extreme heat.

What is Thermal conductivity

It is the property of a material to conduct heat through itself. Materials with high thermal conductivity will conduct more heat than the ones with low conductivity. Some materials do not conduct heat at all because of the insulating properties of materials.

What is Thermal stress?

The stress experienced by a body due to either thermal expansion or contraction is called thermal stress. It can be potentially destructive in nature as it can make the material explode.

In physics, Thermal expansion can be defined as the change in the length, width, height or volume of any material on changing the temperature. Thermal expansion is very evident in solids as atoms are densely packed. Thermal expansion of solids have loads of applications in day to day life.

Thermal Expansion in Metals

It is a well-known phenomenon now that substances expand on heating and contract on cooling. If you heat a body, it alters its dimensions. Depending on the shape of the body.
  1. The expansion can occur in length in which case it is called Linear Expansion.
  2. If we take a square tile and heat it, the expansion will be on two fronts, length and breadth, here it is called Area Expansion.
  3. If we take a cube and heat it, all its sides expand and now the body experiences an increase in the overall volume due to this and it is called Volume Expansion.

Thermal Expansion Formula

Thermal expansion can result in linear expansion or area expansion or volumetric expansion. The corresponding formula is given below along with relevant terms. Thus, the formula used to represent the thermal expansion in a body is
Linear Expamsion:
Δll=αl.ΔT
where,
  • l is the initial length of the solid
  • Δl is the change in length.
  • αl length expansion coefficient
  • ΔT is the temperature difference
Area Expamsion:
ΔAA=αA.ΔT
where,
  • A is the initial area of the solid
  • ΔA is the change in area.
  • αA Area expansion coefficient
  • ΔT is the temperature difference
Volumetric Expamsion:
ΔVV=αV.ΔT
where,
  • V is the initial volume of the solid
  • ΔV is the change in volume.
  • αV volume expansion coefficient
  • ΔT is the temperature difference
Here, the alphal represents the coefficients of linear expansion and it is a characteristic of the substance the body is made of. For example, for the same temperature rise, copper expands almost five times more than glass. Generally, metals expand more and have higher values of alpha compared to gases and liquids.

Volumetric Expansion Coefficient

It is important that we consider the volumetric thermal expansion of substances since most of the things we use in real life are three dimensional and thereby undergo three-dimensional expansion ie volumetric expansion.

Coefficient Of Thermal Expansion Table

Value of coefficient of thermal expansion of different solids are very important to choose the right material. The table is given below lists the name of the material along with the corresponding coefficient of thermal expansion values
MaterialLinear Expansion Coefficient αl at 20°C 10-6K-1Volumetric Expansion Coefficient αvat 20°C 10-6K-1
Quarts0.591.77
Diamond13
Stainless steel10.1~17.330.3~51.9
Steel11~1333.0~39.0
Iron11.835.4
Concrete1236

Thermal Expansion Of Solids Examples

One can observe a plethora of applications of Thermal expansion in day to day life. Some of them are:
  • Metal hot water heating pipes should not be used in long straight lengths
  • Metal framed windows need rubber spacers
  • Large structures and mega constructions such as railways, bridges need expansion joints in the structures to avoid sub kink
  • Thermometers are another example of an application of thermal expansion
In the case of the thermometer, the liquid is constrained to flow in only one direction that is along the tube due to changes in volume brought about by changes in temperature. The working principle of mercury thermometer is explained below.

Mercury Thermometer

Thermal expansion is the basic principle that a thermometer works on. The mercury in the reservoir at the bottom of the thermometer is immersed in a hot or cold object. On doing so, the mercury in the thermometer contracts and expands changing the level indicated on the thermometer.
The thermometers are always calibrated and after a few minutes, the level of mercury inside becomes stable and unchanging. This new level with the calibrated thermometer tells us the temperature of the object we are measuring. The same principle of thermal expansion applies to gases as well. The constant volume gas thermometer is an example of the application of thermal expansion in gases.
In this article, you learnt about the thermal expansion of metals and their reactions to heat in general. In the next article, you will find an explanation about the Anomalous expansion of water, the phenomenon that prevents all the water in the world from freezing over. Also, do read physics related articles mentioned below to enhance your knowledge

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