A spherical black body with a radius of $$12$$ cm radiates $$450$$ W power at $$500$$ K. If the radius were halved and the temperature is doubled, the power radiated in watts would be:
1. $$450$$
2. $$1000$$
3. $$1800$$
4. $$225$$

72%
From NCERT
NEET - 2017
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Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at temperature t °C, the power received by a unit surface of the earth (normal to the incident rays) at a distance from the centre of the sun is:
(where σ is Stefan’s constant.)

1. $\frac{4{\mathrm{\pi r}}^{2}{\mathrm{\sigma t}}^{4}}{{R}^{2}}$

2. $\frac{{r}^{2}\sigma \left(t+273{\right)}^{4}}{4\mathrm{\pi }{R}^{2}}$

3. $\frac{16{\pi }^{2}{r}^{2}{\mathrm{\sigma t}}^{4}}{{R}^{2}}$

4. $\frac{{r}^{2}\sigma \left(t+273{\right)}^{4}}{{R}^{2}}$

65%
From NCERT
AIPMT - 2007
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A black body is at 727 °C. It emits energy at a rate that is proportional to:

1. $\left(727{\right)}^{2}$

2. $\left(1000{\right)}^{4}$

3. $\left(1000{\right)}^{2}$

4. $\left(727{\right)}^{4}$

80%
From NCERT
AIPMT - 2007
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We consider the radiation emitted by the human body. Which of the following statements is true:

 1 The radiation emitted is in the infrared region 2 The radiation is emitted only during the day 3 The radiation is emitted during the summers and absorbed during the winters 4 The radiation emitted lies in the ultraviolet region and hence is not visible
62%
From NCERT
AIPMT - 2003
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Which of the following is closest to an ideal black body?

 1 Black lamp 2 Cavity maintained at a constant temperature 3 Platinum black 4 A lump of charcoal heated to high temperature