light and black body radiation

• specular reflection is when parallel rays hit a smooth surface and reflects in a single direction ( mirror )
• diffuse reflection is whne parallel rays hits an uneven surface and scatters
• opaque is when an object absorbs or reflects all light and none passes through
• translusent is when light scatters as it transmitts ( frosted window )
• an apple absorbs all other wavelengths but pigment reflects red so it appears red
• if a material is white then all wavelengths are reflected
• with a blue filter on an apple, no red wavelengths passes only blue wavelengths the apple appears black
• all objects emit and absorb infared radiation
• infared radiation rate depends on

  • temperature
  • nature of the surface
• the perfect black body emits and aborbs all inared radiation
• temperature determines

  • rate of emission and length of wavelength
  • as it gets hotter , intensity of shorter wavelengths increases
  • as an object gets hotter it glows red then white because the wavelengths get shorter
• the perfect balance

  • as the ground heats up on a sunny day , the temperature increases
  • at first absortion rate is faster than emitting rate
  • as temperature increases , more is emitted
  • eventually emission = absorption ( constant temperature is achieved )
• the temperature of earth depends on

  • how much energy is recieved from the sun
  • how much is reflected back into space
  • gases in the atmosphere
• transparent is when an object transmits light coherently and theres a clear picture
• if a material is black then all wavelengths are being absorbed