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. \(225\)
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 R from the centre of the sun is:
(where σ is Stefan’s constant.)
1.
2.
3.
4.
A black body is at 727 °C. It emits energy at a rate that is proportional to:
1.
2.
3.
4.
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 |
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 |