Which instrument is used to detect infrared rays?

If a vessel with black spots is heated to a very high temperature and then taken into a dark room,then:

Three identical metal spheres (of same surface area) have red,black,and white colors and they are heated up to the same temperature. They are allowed to cool. Arrange them from maximum rate of cooling to minimum rate of cooling.

Out of the following, which statement is $NOT$ true about black body radiation?

We consider the radiation emitted by the human body,which of the following statements is true?

$A$ thermopile is used for: