We consider the radiation emitted by the human body. Which of the following statements is true ?
(a) The radiation is emitted only during the day
(b) The radiation is emitted during the summers and absorbed during the winters
(c) The radiation emitted lies in the ultraviolet region and hence is not visible
(d) The radiation emitted is in the infra-red region
Pick out the statement which is not true .
(a) IR radiations are used for long distance photography
(b) IR radiations arise due to inner electron transitions in atoms
(c) IR radiations are detected by using a bolometer
(d) Sun is the natural source of IR radiation
A hot and a cold body are kept in vacuum separated from each other. Which of the following cause decrease in temperature of the hot body ?
(d) Temperature remains unchanged
Certain substance emits only the wavelengths and when it is at a high temperature. When this substance is at a colder temperature, it will absorb only the following wavelengths ?
(c) and (d) and
As compared to the person with white skin, the person with black skin will experience
(a) Less heat and more cold (b) More heat and more cold
(c) More heat and less cold (d) Less heat and less cold
Which of the following statements is wrong ?
(a) Rough surfaces are better radiators than smooth surface
(b) Highly polished mirror like surfaces are very good radiators
(c) Black surfaces are better absorbers than white ones
(d) Black surfaces are better radiators than white