Heat and Thermodynamics 3 Question 19

19. A spherical black body with a radius of 12cm radiates 450W power at 500K. If the radius were halved and the temperature doubled, the power radiated in watt would be

(a) 225

(b) 450

(c) 900

(d) 1800

(1997,1M)

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Answer:

Correct Answer: 19. (d)

Solution:

  1. Power radiated (surface area) (T)4. The radius is halved, hence, surface area will become 14 times. Temperature is doubled, therefore, T4 becomes 16 times.

New power =(450)(14)(16)=1800W.



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