physics P1 (2)

Infra-red radiation

a prism splits the light into its spectrum of colours
an infra-red sensor was placed in the spectrum and the intenisty recorded
the sensor was also placed either side of the spectrum and the temperature recorded
before violet- 4W/m2
visible spectrum- 6-24 W/m2
beyind red- 50W/m2
infra-red radiation lies beyond the visible light spectrum
em spectrum: large waves (radio) getting smaller (microwaves, visible light, x-rays) smallest waves (cosmic rays)
black emits the radiation but silver doesn't emit the radiation
the black absorbs the infra-red radiation but the silver reflects the radiation

Thermal radiation

radiate means to emit out from a source and radiation is the term used to describe the energy that spreads out
thermal (infra-red) radiation is the transfer of energy by infra-red waves
infra-red waves are part of the electromagnetic spectrum
all objects emit (give out) and absorb (take in) thermal radiation
the hotter the object, the more thermal radiation it radiates
infra-red radiation can travel through a vacuum
this is how we get heat energy from the sun
infra-red radiation can be focused eg. in a solar oven, just like light can be focused by a curved mirror

Absorbers and emitters of radiation

when an object absorbs infra-red radiation its temperature rises
the energy carried by the electromagnetic wave makes the atoms in the material vibrate more vigorously
good absorbers of radiation are dark and dull (or matt) surfaces
they are also good emitters or radiation, ie they give out well
if these surfaces were not both good absorbers and good emitters everything would just get hotter and hotter
poor absorbers or radiation are light, shiny surfaces which reflect infra-red radiation rather than absorb it
these surfaces are also poor emitters, reflecting the radiation back to the emitter

Kinetic theory

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