5 Questions
Explain what black-body radiation is and how it is related to a body in thermodynamic equilibrium with its environment.
Black-body radiation is the thermal electromagnetic radiation emitted by a black body in thermodynamic equilibrium with its environment. It has a continuous spectrum of wavelengths inversely related to intensity, depending only on the body's temperature.
How can the thermal radiation emitted by many ordinary objects be approximated?
The thermal radiation emitted by many ordinary objects can be approximated as blackbody radiation.
Why is blackbody radiation still a good first approximation for the energy emitted by planets and stars, even though they are not in thermal equilibrium with their surroundings?
Blackbody radiation is still a good first approximation for the energy emitted by planets and stars because it characterizes the radiation emitted by these objects, even though they are not in thermal equilibrium with their surroundings.
What is the significance of a perfectly insulated enclosure in relation to blackbody radiation?
A perfectly insulated enclosure in thermal equilibrium internally contains blackbody radiation and will emit it through a small hole made in its wall, provided the hole has a negligible effect upon the equilibrium.
At what temperature does a black body radiate mostly in the infrared spectrum, which cannot be perceived by the human eye?
A black body at room temperature (23 °C (296 K; 73 °F)) radiates mostly in the infrared spectrum, which cannot be perceived by the human eye.
Study Notes
Black-body Radiation
- Black-body radiation is the thermal radiation emitted by a body in thermodynamic equilibrium with its environment, characterized by a continuous spectrum of electromagnetic radiation.
- The concept of a black body is an idealized model, where a body absorbs all the electromagnetic radiation that falls on it, without reflecting or transmitting any radiation.
Approximating Thermal Radiation
- The thermal radiation emitted by many ordinary objects can be approximated by considering them as black bodies, since they are often in thermal equilibrium with their surroundings.
- This approximation is valid because most objects are good absorbers of radiation and can be treated as ideal black bodies.
Planets and Stars
- Blackbody radiation is still a good first approximation for the energy emitted by planets and stars, despite not being in thermal equilibrium with their surroundings.
- This is because the radiation they emit is largely due to their internal thermal energy, rather than interactions with their environment.
Perfectly Insulated Enclosure
- A perfectly insulated enclosure is a crucial concept in blackbody radiation, as it allows the radiation to be in thermal equilibrium with the enclosure.
- The enclosure absorbs and re-emits the radiation, establishing a continuous spectrum of electromagnetic radiation.
Temperature and Infrared Spectrum
- A black body radiates mostly in the infrared spectrum, which cannot be perceived by the human eye, at a temperature of around 500-800 K (227-527°C).
- This is significant because it indicates that objects at this temperature range emit radiation primarily in the infrared range, rather than in the visible spectrum.
Test your knowledge of black-body radiation with this quiz! Explore the specific spectrum of wavelengths and their relation to intensity, all dependent on temperature. Ideal for physics enthusiasts and students studying thermodynamics and electromagnetic radiation.
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