1 Marks Question

Question 11 Mark

Standing in the sun is more pleasant on a cold winter day than standing in shade. Is the temperature of air in the sun considerably higher than that of the air in shade?

Answer

The heat coming from the sun to us is through the radiation. On colder winter days, when we stand in shade, we do not get the heat of the sun from the radiation.
Though we feel cool in the shade, the temperature of the air in shady as well as non-shady regions is the same.

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Question 21 Mark

The temperature of the atmosphere at a high altitude is around $500^{\circ} \mathrm{C}$. Yet an animal there would freeze to death and not boil. Explain.

Answer

The temperature of the atmosphere at a high altitude is around $500^{\circ} \mathrm{C}$, but density of air molecule is extremely low at this height.
So, very less molecules of air collide with the body of the animal and transfer very less amount of heat. That is why the animal present there would freeze to death instead boiling.

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Question 31 Mark

Assume that the total surface area of a human body is $1.6m^2$ and that it radiates like an ideal radiator. Calculate the amount of energy radiated per second by the body if the body temperature is $37^\circ$ C. Stefan constant $\sigma$ is $6.0 × 10^{-8} Wm ^{-2}K^{-4}$.

Answer

$\text{A}=1.6\text{m}^2,\ \text{T}=37^\circ\text{C}=310\text{K},\ \sigma=6.0\times10^{-8}\text{w/m}^2\text{-K}^4$
Energy radiated per second
$=\text{A}\sigma\text{T}^4=1.6\times6\times10^{-8}\times(310)^4$
$=8865801\times10^{-4}$
$=886.58\approx887\text{J}$

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