IB Physics Emissivity

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A tutorial sheet of questions on emissivity is given below.

  1. What is the emissivity of a perfect black body?
  2. Is emissivity the same as albedo?
  3. A metal sphere of radius 2.50 cm is placed in a vacuum and has a surface temperature 523 °C. The intensity of the radiation from the sphere at a distance of 12.0 cm from its centre is 2.37 kW m-2. Find the emissivity of the sphere.
  4. Does emissivity have an effect on the peak wavelength in the radiation spectrum of an object?
  5. Determine the peak wavelength in the radiation spectrum of the sphere in question 3.
  6. Would a human eye "see" the sphere in question 3?
  7. Infra red radiation has a wavelength between 750 nm and 1.0 mm. Visible light has wavelength between 380 nm and 750 nm. By referring to a Planck radiation curve, determine the ratio of the total energy emitted by the sphere as infra red radiation to that emitted as visible light.