Thermal Radiation: Stefan–Boltzmann Law, Greenhouse Effect, and Applications

All flashcards

Thermal radiation

Energy emitted by an object as electromagnetic waves because of its temperature.

Stefan–Boltzmann law

For an object's emitted radiative power, $P=\sigma e A T^4$, where $e$ is emissivity, $A$ is area, and $T$ is absolute temperature.

Emissivity

A measure, from 0 to 1, of how effectively a surface emits radiation compared with an ideal blackbody.

Natural greenhouse effect

Atmospheric absorption and re-emission of some terrestrial infrared radiation helps keep Earth's surface warmer.

Thermograph

An image that represents patterns of temperature across a surface.

Quiz questions

1. Which process transfers energy from the Sun to Earth across the vacuum of space?Answer: Radiation carried by electromagnetic waves.
2. Which equation gives an object's emitted radiative power?Answer: $P=\sigma e A T^4$
3. An object is cooler than uniform-temperature surroundings. What is the sign of its net radiative heat-transfer rate into the object?Answer: Positive, because the surroundings are hotter than the object.
4. Why can dark, matte asphalt absorb more sunlight than a nearby light, reflective sidewalk?Answer: Dark, matte surfaces generally absorb radiation more effectively.
5. How do greenhouse gases such as carbon dioxide contribute to the natural greenhouse effect?Answer: They absorb some terrestrial infrared radiation and emit radiation in different directions.