Thermal Properties of Matter - Result Question 41
42. The radiant energy from the sun, incident normally at the surface of earth is $20 k cal / m^{2}$ $min$. What would have been the radiant energy, incident normally on the earth, if the sun had a temperature, twice of the present one?[1998]
(a) $160 k cal / m^{2} min$
(b) $40 k cal / m^{2} min$
(c) $320 k cal / m^{2} min$
(d) $80 k cal / m^{2} min$
Show Answer
Answer:
Correct Answer: 42. (c)
Solution:
- (c) According to Stefan’s law, $E \propto T^{4}$
$\frac{E_1}{E_2}=\frac{T_1^{4}}{T_2^{4}}$ or $\frac{20}{E_2}=\frac{T^{4}}{2^{4} T^{4}}$
$\Rightarrow E_2=320 kcal / m^{2}$. $min$.
