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.

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.