thermal radiation

What is thermal radiation?

Infrared

How is it different to convection and conduction?

It can transfer energy through a vacuum

So it involves the transfer of heat directly from one object to another, without heating up a medium connecting the two objects.

By which means can the sun heat up the earth?

Radiation

Emission of thermal radiation

Any object/substance with a temperature above absolute zero emits thermal radiation.

The higher the temp of an object, the higher rate at which it emits thermal radiation

When an object emits thermal radiation, thermal energy of the object is transferred to energy of the radiation, so its temperature would decrease.

Three possible outcomes when thermal radiation hits an object

Absorption

Transmission

Reflection

When an object absorbs thermal radiation

The energy of the radiation is transferred to thermal energy of the object. So, if an object where to absorb TR without any other energy transfers occurring, its temperature would increase

Emission and absorption combined

If an object is at a higher temperature than its surroundings, then it emits radiation at a higher rate than its surroundings absorbs it

If an object is at a lower temperature than its surroundings, then it absorbs thermal radiation at a higher rate than its surroundings emits it

Factors affecting rate of absorption and emission of thermal radiation

Texture of objects surface

Surface area of object

How does a shiny surface affect absorption and emission

They are both lower with shiny surfaces, so matte or dull surfaces promote absorption and emission

How does a smaller surface area affect rates of emission and absorption

The rates are lower for smaller surface area, so larger surface areas have higher rates