BLACK BODY RADIATION

BLACK BODY RADIATION

1. Planck's Distribution

   • The distribution of the radiation intensity with wavelength
   • As Temp Increases the Wavelength of the peak decreases
   • As the Wavelength tends to infinity or to zero the radiation intensity tends to zero
   • Classical physics FAILED to explain Planck's Distribution
     • It expects as the wavelength decreases the radiation intensity increases
     • It can't explains that the intensity of the radiation decreases at high frequency (SHORT WAVELENGTH)

2. It's the thermal radiation which is absorbed or emitted by the black body

   • GR Naming of black body radiation
     • Because the black body absorbs all the radiation falls on it regardless of the wavelength , ACTS AS PERFECT ABSORBER it then re-emits this radiation wholly ACTS AS PERFECT EMITTER

3. Planck explained the black body Phenomenon

   • 1) the radiation was made up of photons (packet of energy)
     • 2) Energy of these atoms aren't continuous but quantized into levels
       • 3) Atoms don't radiate when they stay in one energy level BUT if the vibration atom shifts from a high energy level to a lower one it emits a photon whose energy E=hν
         • 4) Photon energy increases with the frequency BUT their no. decreases with increasing energy

4. USES OF BLACK BODY RADIATION

   • 2- RADAR
     • which depends on the microwaves to determine natural earth's resources
   • 1- SATELLITE :
     • which maps & Photograph the surface of the earth using infrared emitted by the earth in addition to visible light
   • 3- Military Purpose
     • Ex: night vision system which detects & image the moving object in the darks (GR)
       • DUE TO heat radiation which these object re-emits
   • 4- Thermal imaging used in
     • Medecine
       • Tomography
       • Embroyology
     • Criminology
       • since the radiation from a person remains for a while after he has left

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