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 → Laws of Thermodynamics ↓


Zeroth law of thermodynamics


The zeroth law of thermodynamics is a fundamental principle that plays a vital role in understanding how thermal equilibrium works. It may seem complicated, but it's quite simple once you understand it.

Understanding thermal equilibrium

Imagine you have a cup of hot coffee and a metal spoon. If you put the spoon in the coffee, what happens after a while? The spoon gets hotter. Why does this happen? This is due to the principle of reaching thermal equilibrium. In simple terms, objects in contact exchange heat until they reach the same temperature.

Illustration of the coffee and spoon reaching thermal equilibrium cup of coffee spoon

Now, let's think of a third object, say another spoon which is initially at room temperature. If we simply put this new spoon in contact with the first spoon (which is already hot), the two spoons will eventually reach the same temperature due to heat transfer. If these spoons are placed in two different cups of water and the heat level in the water becomes the same, this will clearly reveal the equality of temperature between these three different objects, without putting them in contact together.

Zeroth law explained

The zeroth law of thermodynamics states: if two systems are in thermal equilibrium with a third system, then they will also be in thermal equilibrium with each other.

a = c
b = c
=> a = b

Here, A, B, and C are systems. If A is in thermal equilibrium with C, and B is also in thermal equilibrium with C, then A and B must be in thermal equilibrium with each other.

Visual example

Let us understand this principle in a little more detail:

Illustration of three systems demonstrating the zeroth law A B C

Here, systems A and B are not in direct contact, but both are in contact with system C. The zeroth law shows that if A and C are in equilibrium and similarly for B and C, then A and B will be in equilibrium indirectly.

Importance of zeroth law

The zeroth law is very important because it allows us to define the concept of temperature. Without this law, the idea of temperature would be meaningless because there would be no way to measure or compare the thermal states of different systems.

Consider thermometers: they work on the principle of the zeroth law. When you use a thermometer to take your body temperature or check the temperature of a liquid, what you are doing is putting the thermometer in thermal equilibrium with the system. The reading stabilizes when both the thermometer and the system reach the same temperature, allowing you to make meaningful temperature comparisons.

Illustration of a thermometer in a liquid Thermometer liquid

Practical example

To make the zeroth law relevant, think of these everyday examples:

  1. Calibration of instruments: Temperature-measuring devices, such as ovens and refrigerators, rely on the zeroth law to ensure that their readings reflect the actual temperatures inside them.
  2. Weather thermometer: Outdoor thermometers must reach thermal equilibrium with the surrounding air to provide accurate temperature readings.
  3. Cooking: When you set a temperature on an oven, the oven needs to reach thermal equilibrium at that temperature before cooking begins. This ensures that the food is cooked properly.

Relation to other laws of thermodynamics

The zeroth law lays the foundation for all the other laws of thermodynamics by establishing the concept of temperature. Other laws, such as the first law of thermodynamics, which deals with energy conservation (often written as ΔU = Q - W), require a clear understanding of temperature and heat flow.

Conclusion

Understanding the zeroth law of thermodynamics helps us understand how temperature measurements work and how heat attempts to achieve equilibrium between systems. It teaches us that discussing equilibrium does not require physical contact between all objects, thanks to the bridging role of a third system. Remember, the primary contribution of the zeroth law is that it defines temperature as a fundamental and intuitive concept.


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Zeroth law of thermodynamics

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