Heat travels through vacuum by

An ideal black body at room temperature is thrown into a furnace. It is observed that:

$A$ solid cylinder of length $L$ and radius $r$ is heated up to the same temperature as that of a cube of edge length $a$. If both have the same material,volume,and are allowed to cool under similar conditions,then the ratio of the amount of radiation emitted will be (Neglect radiation emitted from the flat surfaces of the cylinder).

Which instrument is used to detect infrared rays?

The absorption coefficient value of a perfect black body is

The spectrum of black body radiation is a ...... .