The rate of radiation of energy from a hot object is maximum,if its surface is ...........

When a body has the same temperature as that of its surroundings,which of the following statements is true?

Why is the Sun considered a perfect black body?

Which of the following statements does not hold good for thermal radiation?

$Assertion :$ $A$ body that is a good radiator is also a good absorber of radiation at a given wavelength.
$Reason :$ According to Kirchhoff's law,the absorptivity of a body is equal to its emissivity at a given wavelength.

At a certain temperature for a given wavelength,the ratio of the emissive power of a body to the emissive power of a black body in the same circumstances is known as: