physics P1 (2)

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  • Created by: haidee
  • Created on: 02-04-12 15:23

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

  • 1. solid: the particles can only vibrate…

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