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Have you ever wondered how a thermometer determines your body temperature, why ice melts, or why metals feel colder than wood? Class 11 Physics Chapter 11: Thermal Properties of Matter provides a beautiful explanation of all these everyday phenomena. This chapter explains the effects of heat on solids, liquids, and gases as well as how variations in temperature lead to physical changes in matter. these NCERT notes for Class 11 Physics is prepared by subject matter expert in accordance with the most recent CBSE syllabus, and they are excellent for tests like the CBSE, JEE, and NEET.
In these NCERT notes for class 11 physics, you will explore important topics like heat transfer (conduction, convection, and radiation), specific and latent heat, Newton’s law of cooling, and thermal expansion etc. You will also find important formulas, simple explanations and relatable examples to make learning easier. Whether you are revising for boards or competitive exams, these NCERT notes for class 11 are very helpful for quick and effective understanding.
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Temperature is the measurement of a body's degree of hotness or coolness.
Example:-A cup of hot soup or an ice cream scoop
Heat is a kind of energy that is exchanged via temperature difference between two (or more) systems or between a system and its surroundings.
For example, a cup of hot coffee might be regarded an object or system, whereas everything else is the environment.
As a result of the temperature difference, heat will move from one thing to another.
The SI unit of Heat is joule.
A thermometer is used to determine the temperature.
In, liquid-in-glass thermometers, mercury and alcohol are regularly used liquids.
The following graph depicts the relationship between temperature in Celsius and Fahrenheit graphically:-
Where tf means Fahrenheit temperature
tc means Celsius temperature
A thermometer that employs any gas, on the other hand, will produce the same readings regardless of the gas used since all gases expand at the same rate at low temperatures.
The following variables are used to characterise the behaviour of gas:
Quantity(mass)
Pressure
Volume
Temperature
Gases with a low density obey the following rules: -
1. Boyle’s Law– In this law, the product of PV = constant(when temperature T is constant)
2. Charles’ Law- In this law, the ratio of V/T = constant (when pressure P is constant)
When both of the preceding principles are combined, the equation becomes PV = RT, where R stands for universal gas constant.
The minimal absolute temperature of an ideal gas is defined as Absolute Zero.
We get a straight line if we plot pressure versus temperature and then extend the line backwards to the x-axis, as seen in the graph below.
The lowest temperature measured (experimentally) was -273.15 °C, which is known as absolute zero.
The relationship between temperature in Kelvin and temperature in Celsius is provided by
Thermal expansion is the phenomenon of a body's dimensions expanding as its temperature rises.
Expansion in length is known as linear expansion.
Expansion in the area is known as area expansion.
Volume Expansion: This is a term that refers to the increase in volume of anything.
The term "linear expansion" refers to the length of anything expanding as the temperature rises.
The term "linear expansion" refers to a fractional change in length or how the length changes in relation to the original length.
ΔL is the length change, L is the initial length, ΔT is the temperature change, and αL is the linear coefficient of thermal expansion.
The term "area expansion" refers to the expansion of an area as a result of an increase in temperature.
There is an increase in both length and width when an area is expanded.
Where αa = coefficient of area expansion.
It is defined as the expansion of volume as a result of an increase in temperature.
This indicates that a substance's length, width, and height have increased.
Where αv = coefficient of volume expansion.
At 4 °C, water has the highest density.
When the temperature drops below 4 °C, the water expands, and the density falls.
Because of this feature, water in lakes and ponds only freezes at the top layer and not at the bottom, but if the water freezes at the bottom as well, animal and plant life would be unable to survive.
A quantity termed the heat capacity of a substance characterises the change in temperature of a substance when a particular amount of heat is absorbed or rejected by that substance.
Where ΔQ is the amount of heat supplied to the substance and ΔT change in its temperature.
Specific heat is the amount of heat received or rejected per unit mass by a substance to change its temperature by one degree.
The heat capacity per mole is the amount of heat (in moles) absorbed or rejected by a substance to change its temperature by one unit.
The molar specific heat capacity (Cp) is defined as follows:
The equivalent molar specific heat capacity at constant pressure is called molar specific heat capacity at constant pressure if the gas is retained at constant pressure during the heat transfer (Cp).
The equivalent molar specific heat capacity at constant volume is called molar specific heat capacity at constant volume if the volume of the gas is maintained during the heat transfer (Cv).
The word calorimetry comes from two parts:
Calorie, which means "heat"
Metry which means "measuring"
So, calorimetry is the process of measuring heat.
It involves the transfer of heat from a hotter body to a cooler body, while making sure that no heat is lost to the surroundings.
The basic idea behind calorimetry is that the heat lost by one body is equal to the heat gained by another. The device used to measure this heat transfer is called a calorimeter.
A change of state is when a substance transitions from one form (solid, liquid, or gas) to another. For example:
Melting is when a solid (like ice) turns into a liquid (like water).
Fusion is the process where a liquid (like water) turns into a solid (like ice).
In thermal equilibrium, there’s no heat gain or loss. The melting point of a substance is the temperature at which its solid and liquid states are in balance (equilibrium).
Normal Melting Point: This is the temperature at which a substance melts under standard atmospheric pressure.
Regelation is the process where pressure lowers the freezing point of water, allowing ice to melt under pressure and refreeze when the pressure is reduced.
Vaporization is the process in which a liquid changes into a gas (for example, water turning into steam).
Sublimation is when a solid directly turns into a gas without becoming a liquid first. During sublimation, both the solid and gas forms exist in thermal equilibrium.
Latent heat is the amount of heat energy required to change the state of a substance without changing its temperature. For example, during melting or boiling, a substance absorbs or releases heat but its temperature stays constant. There are two main types: latent heat of fusion (solid to liquid) and latent heat of vaporization (liquid to gas). This concept helps explain why ice melts or water boils at specific temperatures.
Heat transfer refers to the process by which thermal energy moves from a body at a higher temperature to one at a lower temperature. This transfer can occur in three primary ways:
Conduction – Transfer of heat through direct contact, mainly in solids. For example, a metal rod getting hot when one end is placed in a flame.
Convection – Transfer of heat through the movement of fluids (liquids or gases). Warm fluids rise and cooler fluids sink, creating a convection current. For instance, boiling water in a pot.
Radiation – Transfer of heat without a medium, in the form of electromagnetic waves. This is how the Sun heats the Earth.
Newton's Law of Cooling states that the rate at which a hot object cools down is directly proportional to the difference in temperature between the object and its surroundings, provided this difference is small. In simple words, the hotter the object compared to its surroundings, the faster it loses heat.
Where:
Vaporization :-Vaporization is the process of changing from a liquid to a gas.
The transition from a liquid to a vapour (or gas) is known as vaporisation.
Temperature is the measurement of a body's degree of hotness or coolness.
Example:-
A cup of hot soup or an ice cream scoop
Thermal Equilibrium: During this state, there is no heat loss or gain.
Sublimation:-Sublimation is the transformation of a solid into a gas.
Both the solid and vapour states of a substance coexist in thermal equilibrium throughout the sublimation (solid converts to vapour without going through liquid state) process.
No, the NCERT notes for Class 11 Physics chapter 10 do not include all of the important derivations. This NCERT note summarises the chapter's important points and equations and can be used to review the chapter's Thermal Properties of Matter.
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