Temperature and radiation
In a nutshell
All objects continuously emit and absorb infrared radiation. The amount of radiation emitted or absorbed depends on the temperature and surface of the object.
Radiation
Definition
The emission of energy as electromagnetic waves.
Infrared radiation
All objects continuously emit and absorb infrared radiation. Objects emit radiation from their surfaces. The higher the temperature of the object, the more infrared radiation the object emits in a given time.
Depending on whether the object emits or absorbs more, the temperature of the object will change.
Changes in an object | Emits... | Absorbs... |
Cooling down | More | Less |
Heating up | Less | More |
Constant temperature | Same | Same |
The surface of an object also affects the amount of radiation emitted or absorbed. A black object with a matte surface is better at absorbing and emitting radiation than a white, shiny object.
EM radiation
It's not just IR radiation that objects emit. Objects emit all types of electromagnetic radiation due to their thermal stores.
The hotter an object is, the higher the frequency of EM radiation the object emits.
Curiosity: A metal at room temperature will emit infrared radiation. As it heats up the frequency of EM radiation emitted will increase. This goes from infrared to visible light frequencies - starting at the red frequencies of light. This is why metals glow when they are heated.
The Earth's temperature
The temperature of the Earth depends on the amount of radiation it absorbs and emits.
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During the day, radiation is absorbed from the Sun which causes in increase in local temperature.
At night, less radiation is absorbed than emitted which causes a decrease in local temperature.
Changes to the Earth's atmosphere can affect its temperature. If the atmosphere absorbs more radiation than it emits, the overall temperature of the Earth will increase. This is known as global warming.
The changes to the Earth's atmosphere are caused by greenhouse gases. These gas molecules absorb more of the radiation that is emitted by the Earth's surface. This stops it from being emitted and means the atmosphere is absorbing more radiation than it emits.