The Sun emits electromagnetic energy at a rate of $3.9 \times 10^{25} \ W$. Its radius is $6.96 \times 10^8 \ m$. The intensity of sunlight at the solar surface in $W \ m^{-2}$ is:

If the temperature of the sun is decreased by $1 \%$,then the value of the solar constant will change by ........... $\%$

$A$ black rectangular surface of area $A$ emits energy $E$ per second at $27^{\circ}C$. If the length and breadth are reduced to half of their initial values and the temperature is raised to $327^{\circ}C$, then the energy emitted per second becomes: (in $E$)

$A$ black body is at $727^\circ C$. It emits energy at a rate which is proportional to

$A$ sphere and a cube,both made of copper,have equal volumes and are black. They are allowed to cool at the same temperature and in the same atmosphere. The ratio of their rate of loss of heat is:

Suppose the sun expands so that its radius becomes $100$ times its present radius and its surface temperature becomes half of its present value. The total energy emitted by it then will increase by a factor of