Grade 10
  1. Mechanics  1.1. Dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two dimensions  1.1.3. Displacement and Distance  1.1.4. Speed and Velocity  1.1.5. Acceleration  1.1.6. Graphical representation of motion  1.1.7. Equations of motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Projectile motion  1.1.10. Relative speed  1.2. Dynamics  1.2.1. Newton's Laws of Motion  1.2.2. Inertia and mass  1.2.3. Force and its types  1.2.4. action and reaction force  1.2.5. Friction and its effects  1.2.6. Coefficient of friction  1.2.7. Circular motion  1.2.8. Centripetal force and centripetal acceleration  1.2.9. Momentum and Impulse  1.2.10. Conservation of momentum  1.2.11. Newton's third law and applications  1.3. Work, Energy and Power  1.3.1. Work done by the force  1.3.2. Work–energy theorem  1.3.3. Kinetic energy  1.3.4. Potential energy  1.3.5. Mechanical energy  1.3.6. Energy Conservation  1.3.7. Power and efficiency  1.3.8. Renewable and non-renewable energy sources  1.4. Gravitational force  1.4.1. Newton's law of universal gravitation  1.4.2. Gravitational field and field strength  1.4.3. Acceleration due to gravity on different planets  1.4.4. Kepler's laws of planetary motion  1.4.5. Orbits and satellites  1.4.6. Weight and apparent weight  1.4.7. Gravitational potential energy
  2. Properties of matter  2.1. States of matter  2.1.1. Solid, liquid and gas  2.1.2. Molecular structure of matter  2.1.3. Intermolecular forces  2.1.4. Plasma and Bose–Einstein condensate  2.2. Pressure  2.2.1. Definition of Pressure  2.2.2. Pressure in liquids  2.2.3. Atmospheric pressure  2.2.4. Pascal's principle  2.2.5. Archimedes' Principle and Buoyancy  2.2.6. Surface tension and capillarity  2.3. Elasticity  2.3.1. Hooke's law  2.3.2. Stress and strain  2.3.3. Elastic Limit and Modulus of Elasticity  2.3.4. Applications of Elasticity
  3. Thermal physics  3.1. heat and temperature  3.1.1. Difference Between Heat and Temperature  3.1.2. Temperature scale  3.1.3. Thermal expansion  3.1.4. Thermal equilibrium  3.2. Heat transfer  3.2.1. Conductivity  3.2.2. Convection  3.2.3. Radiation  3.2.4. Insulation and its applications  3.3. Thermal properties of matter  3.3.1. Specific heat capacity  3.3.2. Latent heat and phase change  3.3.3. Boiling and Melting Point  3.3.4. Heat engines and refrigeration  3.4. Laws of Thermodynamics  3.4.1. Zeroth law of thermodynamics  3.4.2. First law of thermodynamics  3.4.3. Second law of thermodynamics  3.4.4. Carnot cycle
  4. Waves and optics  4.1. Nature and properties of waves  4.1.1. Types of waves in nature and properties of waves  4.1.2. Transverse and longitudinal waves  4.1.3. Wave parameters  4.1.4. Reflection and refraction of waves  4.1.5. Superposition and Interference  4.1.6. Standing Waves and Resonance  4.1.7. Doppler effect  4.2. Sound waves  4.2.1. Characteristics of sound waves  4.2.2. Speed of sound in different mediums  4.2.3. Applications of sound waves  4.2.4. Ultrasound and its uses  4.3. Light Waves and Optics  4.3.1. Nature of light  4.3.2. Reflection of light  4.3.3. Laws of reflection  4.3.4. Mirrors and Image Formation  4.3.5. Refraction of light  4.3.6. Snell's Law  4.3.7. Lenses and Image Formation  4.3.8. Total internal reflection and critical angle  4.3.9. Optical fibre  4.4. Optical Instruments  4.4.1. Microscope  4.4.2. Telescope  4.4.3. Human eye and vision defects  4.4.4. Camera and its working principle
  5. Electricity and Magnetism  5.1. Electrostatics  5.1.1. Electric charge and its properties  5.1.2. Conductors and Insulators  5.1.3. Coulomb's law  5.1.4. Electric field and field lines  5.1.5. Electric potential and potential difference  5.1.6. Capacitors and Capacitance  5.2. Current Electricity  5.2.1. Electric current and its measurement  5.2.2. Ohm's law  5.2.3. Resistance and resistivity  5.2.4. Series and Parallel Circuits  5.2.5. Electric power and energy  5.2.6. Kirchhoff's Laws  5.3. Magnetism and Electromagnetism  5.3.1. Magnetic field and field lines  5.3.2. Magnetic effects of electric current  5.3.3. Electromagnetic induction  5.3.4. Faraday's laws of electromagnetic induction  5.3.5. Transformers and Applications  5.3.6. AC and DC current
  6. Modern Physics  6.1. Nuclear physics  6.1.1. Structure of the atom  6.1.2. Bohr's atomic model  6.1.3. Electron Energy Levels  6.1.4. X-rays and applications  6.2. Radioactivity  6.2.1. Types of radiation  6.2.2. Half-life and radioactive decay  6.2.3. Nuclear reactions and applications  6.2.4. Fission and Fusion  6.3. Quantum physics  6.3.1. Wave–particle duality  6.3.2. Photoelectric effect  6.3.3. Energy quantization  6.3.4. Heisenberg's uncertainty principle
  7. Electronics and Communication  7.1. Semiconductors  7.1.1. Conductors, Insulators and Semiconductors  7.1.2. Diodes and their applications  7.1.3. Transistors and Logic Gates  7.1.4. LEDs and photodiodes  7.2. Communication Systems  7.2.1. Basics of communication  7.2.2. Analog and digital signals  7.2.3. Wireless and optical fibre communication  7.2.4. Radio Waves and Modulation

Grade 10 → Thermal physics → heat and temperature ↓


Thermal equilibrium


Thermal equilibrium is a fundamental concept in thermal physics that refers to the situation where two or more objects reach a state where they no longer exchange heat energy. In thermal equilibrium, all objects involved are at the same temperature, and there is no net flow of thermal energy between them.

Understanding heat and temperature

To understand the concept of thermal equilibrium, it is important to understand the basics of heat and temperature:

  • Heat is a form of energy that is transferred between objects at different temperatures. It flows from a hotter object to a cooler object and results in changes such as a rise in temperature or a phase change.
  • Temperature, on the other hand, measures how hot or cold something is. It is a measure of the average kinetic energy of the particles in a substance.

A basic example

Consider two objects, one hot and one cold, that are placed in contact. The hot object has a higher temperature, which means that its particles have more kinetic energy than the particles of the cold object. Thermal energy from the hot object will naturally flow toward the cold object. This will continue until both objects reach the same temperature.

When the temperatures become equal, and no further heat exchange occurs, the objects are said to be in thermal equilibrium.

Visualization of thermal balance

hot item cold item

In the figure above, the red circle represents the hot object, and the blue circle represents the cold object. When these objects come into contact, heat will flow from the hot object to the cold object. Eventually, both objects will have the same temperature, achieving thermal equilibrium.

Formulaic representation

When two objects are in thermal equilibrium, this ensures that there is no temperature difference between the objects, so no heat transfer occurs:

T_1 = T_2

where T_1 and T_2 are respectively the temperatures of the two bodies which are in equilibrium.

Real-life example: working thermal equilibrium

Imagine you are making a cup of hot coffee. If you leave it on the table, it is initially hotter than the surrounding air. Over time, the coffee cools down, and you will notice that it eventually reaches room temperature. This happens because the coffee loses heat to the surrounding air until it stops losing heat, which means that the temperature of the coffee and the surrounding air are equal. At this point, they are in thermal equilibrium.

Coffee room air

Applications of thermal equilibrium

Thermal equilibrium plays an important role in many scientific and everyday applications:

  • Thermometer: Thermometers measure temperature based on reaching thermal equilibrium with the surrounding environment. When you place a thermometer in a substance, it reads the temperature of the substance because it achieves thermal equilibrium with it.
  • Climate control: Devices such as air conditioners and heaters work by creating a thermal balance in a certain area, and regulating the temperature to a desired level.
  • Cooking: Thermal equilibrium is fundamental in processes such as baking, where heat must be distributed evenly so that food can cook properly.

Investigate further with a simple experiment

You can explore the concept of thermal equilibrium at home with a simple experiment:

  1. Take two vessels of equal size – fill one with hot water and the other with cold water.
  2. Dip a metal spoon into each pot at once.
  3. Wait for some time and take out the spoons from the container.
  4. Touch the part of the spoon that was dipped in water. Both spoons will feel the same temperature.

This happens because the metal spoon acts as a conductor and helps transfer thermal energy between the two waters until the two reach thermal equilibrium.

The concept of specific heat capacity

It is also important to understand the idea of specific heat capacity when discussing thermal equilibrium. Specific heat capacity is the amount of heat needed to change the temperature of one unit mass of a substance by one degree Celsius. It is represented by:

c = Q / (m * ΔT)

Where:

  • c is the specific heat capacity
  • Q is the heat added or removed
  • m is the mass of the substance
  • ΔT is the change in temperature

Different materials have different specific heat capacities, and this affects how quickly they reach thermal equilibrium.

Thermal equilibrium in different states of matter

The laws of thermal equilibrium apply universally whether objects are solid, liquid or gas. Let's take a look at each state:

  • Solids: In solids, thermal equilibrium may involve conduction, where heat is transferred between particles at fixed positions.
  • Fluids: Here, heat transfer involves conduction and convection, where hot particles move and mix with cold particles.
  • Gases: Convection is even more important in gases, because the particles are free to move around more freely.

Conclusion

Thermal equilibrium is a pervasive and fundamental principle in physics, affecting everything from the design of engines to the daily operation of household appliances. Understanding this concept provides insight into the behavior of substances and heat flow, and is important for explaining why and how objects change temperature.

By exploring a variety of examples and applications, one can see that thermal equilibrium is more than just a theoretical concept; it is a practical, observable phenomenon that profoundly impacts the natural and engineered world.


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Thermal equilibrium

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