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 transfer ↓


Radiation


Introduction to heat transfer

Heat transfer is a fundamental concept in thermal physics, describing the movement of thermal energy from one location to another. Heat can be transferred in three primary ways: conduction, convection, and radiation. Each method operates under different principles and occurs under different conditions. In this explanation, we will focus primarily on radiation, exploring its unique characteristics and looking at how it functions in the transfer of heat.

What is radiation?

Radiation is a method of heat transfer that does not require a medium to transfer thermal energy. Unlike conduction and convection, which rely on particles to carry heat, radiation involves the transfer of energy via electromagnetic waves. This means that radiation can occur even in a vacuum, where no particles are present.

Radiation is the process by which energy, especially heat energy, is emitted by a source and spreads in all directions through empty space or matter. All objects emit energy by radiation, and the amount of energy radiated increases with the temperature of the object.

How does radiation work?

Radiation transfers energy by emitting electromagnetic waves. The emitted waves are often in the infrared part of the electromagnetic spectrum, although high-temperature bodies may also emit visible light and ultraviolet radiation. When these waves strike an object, they may be absorbed, reflected, or transmitted. The absorbed energy increases the energy of the object, often resulting in an increase in temperature.

Examples of radiation

Radiation is all around us, and there are plenty of examples that help explain how this process works:

  • The most prominent example is the heat that reaches the Earth from the Sun. Despite the vacuum of space, solar energy reaches our planet primarily through radiation.
  • A campfire that radiates heat toward people sitting around it. You can feel the heat without even touching the flames or the air around them.
  • A microwaving process in which microwaves (a form of radiation) heat the food inside without touching the food.

Nature of radiant energy

Radiant energy travels in the form of electromagnetic waves. These waves are characterized by their wavelength and frequency. The electromagnetic spectrum includes a wide range of wavelengths, but infrared radiation is most commonly associated with thermal physics. This part of the spectrum is associated with heat and is what most objects emit naturally.

Electromagnetic Spectrum: | | Radio | Microwave | Infrared | Visible | Ultraviolet | X-rays | Gamma rays | |

The wavelength of thermal radiation decreases as the temperature increases. As objects get hotter, they emit more energy at shorter wavelengths, which can change from infrared to visible light, as seen in glowing metals or the Sun.

Blackbody radiation

A blackbody is an idealized physical body that absorbs all incident electromagnetic radiation. An idealized blackbody in thermal equilibrium emits radiation called blackbody radiation. The characteristics of blackbody radiation depend only on the temperature of the body. The Stefan–Boltzmann law describes the power radiated from a blackbody in terms of its temperature:

P = σAT^4

Where:

  • P is the radiated power.
  • σ is the Stefan–Boltzmann constant.
  • A is the surface area of the radiating body.
  • T is the absolute temperature in Kelvin.

Graphically, the intensity of radiation emitted by a blackbody at a given temperature is represented by a curve, often referred to as the Planck curve. As the temperature increases, the peak of this curve shifts to shorter wavelengths, representing the transition from infrared to visible light emission.

Factors affecting radiation

Many factors can affect the amount and type of thermal radiation emitted or absorbed by a surface. These include:

1. Temperature

Higher temperatures result in more energetic and shorter wavelength emissions. This is why a hotter body not only emits more total radiation, but also emits radiation at shorter wavelengths.

2. Surface color and texture

Dark and rough surfaces absorb and emit more radiation than light and smooth surfaces. This is why it is often recommended to wear light-coloured clothing in hot weather, as it reflects more radiation, keeping the body cooler.

3. Surface area

More significant surface areas can emit more radiation. This explains why objects with a large surface area, such as radiators, effectively emit heat into the room.

Applications of radiation

Radiation plays a vital role in various applications, whether naturally occurring or man-made. Some of these are as follows:

1. Solar energy

The Earth's primary source of energy is radiation from the Sun. Solar panels use this energy to convert solar radiation into electricity using photovoltaic cells, a vital process for sustainable energy solutions.

2. Thermal imaging

Infrared radiation is used in thermal imaging to detect heat emitted by objects or living beings. It is widely used in night vision equipment, medical diagnosis, and building inspection to detect heat leaks.

3. Radiation cooling

Understanding radiation helps engineers design systems that effectively dissipate heat through radiative methods. This is important in designing spacecraft and electronics that need to efficiently remove heat in environments where convection is impractical.

Visual example: radiation emission

Consider three objects with different temperatures; a candle flame, a red-hot iron, and an unlit candle. Let's imagine the radiation emitted from each:

In the figure above, the orange circle represents the candle flame, which emits a broad spectrum of radiation, including visible light. The red rectangle represents the red-hot iron, which emits mainly infrared radiation. The lines show the radiation distribution in space.

Conclusion

Radiation is a powerful and essential means of heat transfer. Its ability to conduct without a medium allows it to transfer energy over long distances, through a vacuum, and in a wide variety of conditions. By understanding radiation, we can understand how energy is exchanged naturally and use this knowledge in technology and applications that improve quality of life, provide energy solutions, and expand our understanding of the universe.


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Radiation

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