$A$ body,which emits radiations of all possible wavelengths,is known as

The velocity of heat radiation in vacuum is

Which instrument is used to detect infrared rays?

Define emissivity and absorptivity and give their values for a perfect black body.

Which of the following is best close to an ideal black body?

There is a rough black spot on a polished metallic plate. It is heated up to $1400 K$ approximately and then at once taken into a dark room. Which of the following statements is true?