Radiation is the transfer of energy through electromagnetic waves without requiring a medium. Unlike conduction and convection, it can occur in a vacuum. The Sun’s heat reaching Earth is an example of radiation. It involves the emission, absorption, and transmission of energy in the form of electromagnetic waves.
Chapter 10 of Class 11 Physics covers thermal properties of matter. It explains concepts like temperature and heat and thermal expansion and specific heat capacity and calorimetry. The chapter also discusses heat transfer methods such as conduction and convection and radiation. Additionally it includes laws of thermodynamics and ideal gas laws.
The Stefan-Boltzmann law states that the total energy radiated per unit surface area of a black body per unit time is directly proportional to the fourth power of its absolute temperature.
Mathematically:
P = σ A T⁴
Explanation:
– P: Total power radiated by the black body (in watts, W)
– σ: Stefan-Boltzmann constant (5.67 × 10⁻⁸ W·m⁻²·K⁻⁴)
– A: Surface area of the black body (in square meters, m²)
– T: Absolute temperature of the black body (in kelvins, K)
The law describes the energy radiated by an ideal black body, which absorbs and emits all incident radiation perfectly. The radiative power increases significantly with temperature because of the T⁴ dependence, meaning small temperature changes cause large variations in emitted energy.
Applications:
1. Astrophysics: Calculating the energy output of stars and celestial objects.
2. Thermal Engineering: Designing heat radiators, furnaces, and thermal equipment.
3. Climate Science: Analyzing Earth’s energy balance with solar and terrestrial radiation.
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