Black Body Radiation Flashcards
All 16 cards in this deck
Which bodies emit and absorb infrared radiation?
All bodies (objects), no matter what their temperature.
How does the amount of infrared radiation a body emits in a given time depend on its temperature?
The hotter the body, the more infrared radiation it radiates in a given time.
What is a perfect black body?
An object that absorbs all of the radiation incident on it — it reflects and transmits no radiation.
Why would a perfect black body be the best possible emitter of radiation?
Because a good absorber is also a good emitter.
True or false? A perfect black body reflects some of the radiation that hits it.
False. A perfect black body absorbs all incident radiation and reflects (and transmits) none.
What does the range (and distribution) of wavelengths of radiation emitted by a star depend on?
Its temperature.
On an intensity–wavelength curve, what happens to the peak as the temperature of the body increases?
The peak intensity increases and the peak moves to a shorter wavelength.
In an experiment, hot water in a matt black can cools faster than in a shiny silver can. What does this show?
Matt black surfaces emit infrared radiation at a greater rate than shiny surfaces.
Four identical cubes of cold water, differing only in surface colour, are heated by an infrared heater. Which cube shows the greatest temperature increase, and why?
The matt black cube, because dark matt surfaces are the best absorbers of infrared radiation.
(HT) What is true about the rates of absorption and emission for a body at constant temperature?
It is absorbing radiation at the same rate as it is emitting radiation.
(HT) When does the temperature of a body increase, in terms of radiation?
When the body absorbs radiation faster than it emits radiation.
(HT) When does the temperature of a body decrease, in terms of radiation?
When the body emits radiation faster than it absorbs radiation.
True or false? A body at constant temperature has stopped emitting radiation.
False. It still emits radiation, but absorbs it at exactly the same rate.
(HT) Name three factors that determine the temperature of the Earth.
The rate of absorption of radiation, the rate of emission of radiation, and the reflection of radiation into space.
(HT) What happens to the Earth's temperature if the rate at which the atmosphere and surface emit radiation into space decreases?
The temperature rises, because absorption is then faster than emission.
(HT) What are the steps to explain the temperature change of a body from a radiation diagram?
e.g. a road absorbing sunlight in the daytime
- State the rate of radiation absorbed: the road absorbs radiation from the Sun quickly.
- State the rate of radiation emitted: it emits infrared more slowly than it absorbs.
- Compare the rates to give the change: absorption > emission, so the road's temperature rises.