Black Body Radiation (AQA GCSE Physics): Flashcards
Exam code: 8463
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Define black body radiation.
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Cards in this collection (19)
Define black body radiation.
Black body radiation is the name given to the thermal radiation emitted by all bodies (objects).
Define a perfect black body.
A perfect black body is an object that absorbs all of the radiation incident on it and does not reflect or transmit any radiation.
In which region of the electromagnetic spectrum does black body radiation usually lie?
Black body radiation usually lies in the infrared region, though it could be emitted as visible light or other wavelengths depending on the temperature of the object.
Why is a perfect black body also the best possible emitter of radiation?
A good absorber is also a good emitter, so an object that perfectly absorbs all radiation is also the best possible emitter.
Why does a perfect black body appear black?
Black is the colour seen when all colours from the visible light spectrum are absorbed.
The hotter an object, the ______ infrared radiation it radiates in a given time.
The hotter an object, the more infrared radiation it radiates in a given time.
True or False?
As the temperature of an object increases, the peak of its black body radiation curve moves to a longer wavelength.
False.
As temperature increases, the peak of the curve moves to a lower wavelength and a higher intensity.
As an object gets hotter, what happens to the wavelength of the radiation it emits, and why?
The object emits more thermal radiation, increasing the emitted energy, so the wavelength of the emitted radiation decreases.
What colour of light does an object mainly emit at around 1000 °C and at around 6000 °C?
At 1000 °C an object emits a significant amount of red light. At 6000 °C it mainly emits white or blue light (and some ultraviolet).
Define thermal equilibrium.
An object is in thermal equilibrium when it absorbs radiation at the same rate as it emits it, so its temperature stays constant.
What happens to the temperature of a body if it absorbs radiation faster than it emits it?
The body's temperature increases; it gets hotter.
Why do rescue teams use light-coloured, shiny emergency blankets to keep accident survivors warm?
A light, shiny surface emits less radiation than a dark, matt surface, so less infrared radiation is emitted, keeping the patient warm.
The temperature of a body can be regulated by balancing radiation ______ against radiation ______.
The temperature of a body can be regulated by balancing radiation absorbed against radiation emitted.
What would happen to the temperature of the Earth's surface at night if the Earth had no atmosphere?
It would drop rapidly and by a large amount, as there would be no atmosphere to absorb and re-emit radiation back towards the surface.
Name three greenhouse gases that absorb and reflect back longer-wavelength infrared radiation from the Earth.
Water vapour, methane and carbon dioxide.
Why does the Earth emit thermal radiation with a longer wavelength than the radiation it receives from the Sun?
Because the surface temperature of the Earth is significantly smaller than the surface temperature of the Sun.
Define the Greenhouse Effect.
The Greenhouse Effect is the natural process that warms the Earth's surface using thermal radiation from the Sun.
True or False?
Greenhouse gases absorb longer-wavelength infrared radiation from the Earth and emit it back to the surface.
True.
Greenhouse gases absorb the radiation and then emit it back to the surface, making the Earth warmer than it would otherwise be.
List the three factors that the temperature of the Earth depends on, relating to light and infrared radiation from the Sun.
The rate at which radiation is reflected back into space, absorbed by the Earth's atmosphere or surface, and emitted from the Earth's surface and atmosphere into space.
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