Physics - 2 Energy Transfer by Heating - 2.2 Infrared Radiation & 2.3 More About Infrared Radiation

Infrared radiation

electromagnetic waves with wavelengths that are longer than visible light but shorter than microwaves.

Electromagnetic spectrum:

(from shortest wave to longest)
- gamma rays
- x-rays
- ultraviolet
- visible
- infrared
- microwaves
- radio

Electromagnetic spectrum mnemonic

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... objects emit and absorb infrared radiation

all

The higher the temperature of an object, the ...

more infrared radiation it emits in a given time

a body at a constant temperature...

emits infrared radiation at the same rate as it absorbs it, across a continuous range of wavelengths

Perfect black body

an object that absorbs all the radiation that hits it

A perfect black body does not [2]:

- reflect radiation
- transmit radiation (let it pass through)

A perfect black body is the best [2]:

- absorber
- emitter

What depends on the temperature of the object [2]:

- wavelength
- intensity

Very hot objects emit ... wavelength radiation

shorter

Very hot objects produce:

visible light

An object that is cooling ... more radiation at a higher rate than it ... it

emits, absorbs

An object that is heating up ... more radiation at a higher rate than it ... it

absorbs, emits

Black body radiation graph:

wave speed =

frequency x wavelength

Frequency is measured in

Hertz (Hz)

A good reflector of infrared is [2]:

- light-coloured
- shiny

A good absorber of infrared is [2]:

- dark-coloured
- matte

Absorption and emission of infrared on Earth [3]:

1. infrared radiation from sun warms Earth
2. Earth becomes warm and emits longer-wavelength infrared radiation
3. greenhouse gases absorb this infrared and re-emit it to the ground