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NEET 1998 (AIPMT) · Thermal Radiation: Black Body, Stefan & Wien

Thermal Radiation: Black Body, Stefan & Wien question from NEET 1998 (AIPMT)

Q108NEET 1998 · AIPMTMedium

Thermal Radiation: Black Body, Stefan & Wien

The radiant energy from the sun, incident normally at the surface of earth is 20 kcal/m2 min20\text{ kcal/m}^{2}\text{ min}. What would have been the radiant energy, incident normally on the earth, if the sun had a temperature, twice of the present one?

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Answer: (c)

  1. Energy received on earth ∝\propto power of the sun ∝T4\propto T^4.
  2. T→2TT \to 2T gives a factor 24=162^4 = 16.
  3. 16×20=320 kcal/m2 min16 \times 20 = 320\text{ kcal/m}^2\text{ min}
  4. So the answer is (c) 320 kcal/m2 min320\text{ kcal/m}^2\text{ min}.
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