A radiation blackbody has the shape of a sphere of radius $$r.$$ Its surface is at a temperature $$T$$ (in Kelvin). If the temperature is doubled and the radius is halved, the total rate of radiation emitted from the body:
 1 increases by a factor of $$4$$ 2 increases by a factor of $$2$$ 3 remains unchanged 4 decreases by a factor of $$2$$
Subtopic:  Stefan-Boltzmann Law |
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Ice ($$0^{\circ}$$C) is kept in an insulated reservoir with an opening that is covered at the top with a cloth. When a black cloth $$(B)$$ is placed at the top, the ice melts at $$2$$ g/$$3$$ min. When an ordinary cloth $$(G)$$ is placed, the rate of melting is $$2$$ g /$$5$$ min. The emissivity of $$G$$ is: (assuming that $$B$$ behaves as a blackbody)

 1 $$0.6$$ 2 $$0.3$$ 3 $$0.4$$ 4 $$0.5$$
Subtopic:  Stefan-Boltzmann Law |
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A solid at temperature T1, is kept in an evacuated chamber at temperature T2 > T1 . The rate of increase of temperature of the body is proportional to

1. T2 – T1

2.   $$T^2_2 -T^2_1$$n

3.   $$T^3_2 -T^3_1$$

4.   $$T^4_2 -T^4_1$$

Subtopic:  Stefan-Boltzmann Law |
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A black body at $$227^{\circ}~\mathrm{C}$$ radiates heat at the rate of $$7~ \mathrm{cal-cm^{-2}s^{-1}}$$.  At a temperature of $$727^{\circ}~\mathrm{C}$$, the rate of heat radiated in the same units will be:
1. $$60$$
2. $$50$$
3. $$112$$
4. $$80$$

Subtopic:  Stefan-Boltzmann Law |
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