What is Thermal Physics?
Thermal Physics is the branch of physics that deals with heat, temperature, thermal energy, and the behavior of matter when it is heated or cooled.
Thermal Physics helps us understand everyday situations such as boiling water, melting ice, cooling of hot tea, expansion of metals, working of refrigerators, and transfer of heat from one object to another.
Thermal Physics connects the ideas of heat, temperature, energy transfer, and changes in matter.
Heat and Temperature
Heat and temperature are closely related, but they are not the same.
Temperature tells us how hot or cold a body is.
Heat is a form of energy that flows from a hotter body to a colder body because of temperature difference.
For example, when a hot cup of tea is kept on a table, heat flows from the tea to the surroundings. As a result, the tea cools down.
Learn more about Temperature!
Thermometry
Thermometry is the measurement of temperature.
Temperature is measured using instruments called thermometers. A thermometer works based on the physical change that takes place when temperature changes.
For example, in a liquid-in-glass thermometer, the liquid expands when heated and contracts when cooled.
Common temperature scales are:
- Celsius scale
- Fahrenheit scale
- Kelvin scale
Thermal Expansion
Most substances expand when heated and contract when cooled.
This change in size due to temperature change is called thermal expansion.
Thermal expansion can occur in solids, liquids, and gases.
Examples of thermal expansion are:
- Railway tracks have small gaps to allow expansion in summer.
- Electric wires sag more in hot weather.
- A tight metal lid can be loosened by heating it.
Transfer of Heat
Heat can travel from one place to another.
There are three main modes of heat transfer:
- Conduction
- Convection
- Radiation
Conduction is heat transfer through direct contact. It mainly occurs in solids.
Convection is heat transfer through the movement of liquids or gases.
Radiation is heat transfer without the need for a material medium.
For example, heat from the Sun reaches the Earth by radiation.
Calorimetry
Calorimetry is the measurement of heat.
It is used to calculate the amount of heat gained or lost by a body.
When a hot object and a cold object are brought into contact, heat flows from the hot object to the cold object until both reach the same temperature.
The principle of calorimetry is:
Heat lost by the hot body = Heat gained by the cold body
Specific Heat Capacity
Different substances need different amounts of heat to raise their temperature.
Specific heat capacity is the amount of heat required to raise the temperature of unit mass of a substance by one degree Celsius or one kelvin.
Water has a high specific heat capacity. This means it takes a large amount of heat to raise the temperature of water.
This is why water is used for cooling in engines and why coastal areas have moderate temperatures.
Change of State
Matter exists mainly in three states:
- Solid
- Liquid
- Gas
A substance can change from one state to another when heat is absorbed or released.
Common changes of state are:
- Melting — solid changes into liquid
- Freezing — liquid changes into solid
- Boiling — liquid changes into gas
- Condensation — gas changes into liquid
- Sublimation — solid changes directly into gas
- Deposition — gas changes directly into solid
Latent Heat
During a change of state, heat is absorbed or released, but the temperature of the substance does not change.
This hidden heat is called latent heat.
For example, when ice melts into water at 0°C, heat is absorbed. But the temperature remains 0°C until all the ice has melted.
Similarly, when water boils at 100°C, heat is absorbed, but the temperature remains 100°C while boiling continues.
There are two common types of latent heat:
Latent heat of fusion — heat involved in changing solid into liquid or liquid into solid.
Latent heat of vaporization — heat involved in changing liquid into gas or gas into liquid.
Gas Laws
Gases expand, contract, and change pressure easily.
Gas laws describe the relationship between pressure, volume, and temperature of a gas.
Important gas laws are:
Boyle’s Law
At constant temperature, the pressure of a gas is inversely proportional to its volume.
Charles’s Law
At constant pressure, the volume of a gas is directly proportional to its absolute temperature.
Pressure Law
At constant volume, the pressure of a gas is directly proportional to its absolute temperature.
These laws help us understand the behavior of gases in balloons, syringes, pressure cookers, engines, and weather systems.
Kinetic Theory of Matter
The kinetic theory of matter explains the behavior of matter in terms of tiny particles.
According to this theory, all matter is made up of particles that are constantly moving.
In solids, particles vibrate about fixed positions.
In liquids, particles move more freely.
In gases, particles move rapidly in all directions.
When temperature increases, the particles move faster. When temperature decreases, the particles move slower.
Thermodynamics
Thermodynamics is the study of heat, work, energy, and energy transformations.
It explains how heat can be converted into work and how energy flows in physical systems.
Thermodynamics is used to understand engines, refrigerators, heat pumps, turbines, and many natural processes.
Important ideas in thermodynamics include:
- Internal energy
- Work done by gases
- Heat supplied to a system
- First law of thermodynamics
- Second law of thermodynamics
Learn more about Thermodynamics!
Why Thermal Physics is Important?
Thermal Physics is important because heat and temperature affect almost every physical process around us.
It helps us understand:
- Cooking and heating
- Weather and climate
- Melting and freezing
- Refrigerators and air conditioners
- Engines and machines
- Expansion of materials
- Body temperature regulation
- Energy transfer in nature
Thermal Physics forms an important bridge between everyday experience and deeper physics concepts.
Glossary of Key Terms
Recap of the Key Terms in Thermal Physics
- Boyle’s Law: Gas law relating pressure and volume at constant temperature.
- Calorimetry: Measurement of heat gained or lost by substances.
- Change of State: Conversion of matter from one physical state to another.
- Charles’s Law: Gas law relating volume and absolute temperature at constant pressure.
- Conduction: Transfer of heat through direct contact.
- Convection: Transfer of heat through the movement of liquids or gases.
- Heat: Energy transferred from a hotter body to a colder body due to temperature difference.
- Kinetic Theory: Theory that explains matter in terms of moving particles.
- Latent Heat: Heat absorbed or released during change of state without change in temperature.
- Radiation: Transfer of heat without a material medium.
- Specific Heat Capacity: Heat required to raise the temperature of unit mass of a substance by one degree.
- Temperature: A measure of how hot or cold a body is.
- Thermal Expansion: Increase in size of a substance when it is heated.
- Thermodynamics: Study of heat, work, energy, and energy transformations.
- Thermometer: An instrument used to measure temperature.
Quiz
Recap the concepts you have learnt. Try to answer the questions. You can find the answer to any question by clicking on the icon.
What is Thermal Physics?
Thermal Physics is the branch of physics that deals with heat, temperature, thermal energy, and energy transfer.
What is the difference between heat and temperature?
Heat is energy transferred from a hotter body to a colder body. Temperature tells how hot or cold a body is.
What is thermometry?
Thermometry is the measurement of temperature using thermometers.
Name the three modes of heat transfer.
The three modes of heat transfer are conduction, convection, and radiation.
What is thermal expansion?
Thermal expansion is the increase in size of a substance when it is heated.
What is calorimetry?
Calorimetry is the measurement of heat gained or lost by substances.
What is specific heat capacity?
Specific heat capacity is the heat required to raise the temperature of unit mass of a substance by one degree Celsius or one kelvin.
What is change of state?
Change of state is the conversion of matter from one physical state to another.
What is latent heat?
Latent heat is the heat absorbed or released during change of state without change in temperature.
What does kinetic theory explain?
Kinetic theory explains matter in terms of tiny particles that are constantly moving.
What do gas laws describe?
Gas laws describe the relationship between pressure, volume, and temperature of gases.
What is thermodynamics?
Thermodynamics is the study of heat, work, energy, and energy transformations.