Answer:
(a) This is because a body with large reflectivity is a
poor absorber of heat, and poor absorbers of heat are emitters.
(b)
When we touch a brass tumbler on a chilly day; heat flows from our body to the
tumbler quickly (as thermal conductivity of brass is very high) and as a
result, it appears colder. On the other hand, as the wood a bad conductor, heat
does not flow to the wooden tray from our body, on touching it.
(c)
When the red hot iron piece is in the oven, its temperature TK is given by the
relation,
\[\text{X=l}{{\left[
\frac{\text{mg}}{\text{YA}} \right]}^{\text{1/3}}}=0\cdot 5{{\left[
\frac{0\cdot 1\times 10}{20\times {{10}^{11}}\times 0\cdot 5\times {{10}^{-6}}}
\right]}^{1/3}}\] But, if the red hot iron piece is in the open having the
surrounding temperature \[=1\cdot 074\times {{10}^{-2}}m=1\cdot \text{074 cm}\],
its energy is radiated according to relation,
\[6\cdot
9\times {{10}^{7}}Pa\]
As
the working principle of optical pyrometer is based on the fact that the
brightness of a glowing surface of a body depends upon its temperature.
Therefore, pyrometer gives too low a value for the temperature of red iron in
the open.
(d)
The lower layers of earth's atmosphere reflect infrared radiations from earth
back to the surface of earth. Thus the heat radiation received by the earth
from the sun during the day are kept trapped by the atmosphere. If atmosphere
of earth were not there, its surface would become too cold to live.
(e)
Steam at \[{{100}^{o}}C\] possesses more heat than the same mass of water at \[{{100}^{o}}C\].
One gram of steam at \[{{100}^{o}}C\]possesses 540 calories of heat more than
that possessed by 1 gm. of water at \[{{100}^{o}}C\]. That is why heating
systems based on circulation of steam are more efficient than those based on
circulation of hot water.
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