91Ó°ÊÓ

• The total power radiated by our body we use is given by $\text{Power}=\mathrm{σ}eA{T}^4$

The power radiated is

$\text{Power}=\mathrm{σ}eA{T}^4$

$T=310K$, $A=2m^2$, $e=1$.

$\text{Power}=\left(5.67×{10}^{-8}\mathrm{W}/{\mathrm{m}}^2·{\mathrm{K}}^4\right)\left(2{\mathrm{m}}^2\right)(310\mathrm{K}{)}^4$

$=1050\mathrm{W}$

$≈1000\mathrm{W}$

$≈1.0×{10}^3\mathrm{W}$

$≈1\mathrm{kW}$

Hence, This is the rate at which we would lose energy, if we were naked in empty space .

The rate, the energy we would lose in one day will be

$(1050\mathrm{W})\left(24\mathrm{hr}\right)\left(\frac{3600\mathrm{s}}{1\mathrm{hr}}\right)=\left(9.0×{10}^7\mathrm{J}\right)\left(\frac{1\mathrm{kcal}}{4186\mathrm{J}}\right)$

$=20,000\mathrm{kcal}$

As we can see that it is ten times the numbers of calories that an average person conserves in a day about $\left(2000\right)$. The discrepancy is due to the fact that we are not naked in empty space, most of the energy that we radiate is replaced by energy radiated or conducted back to us by our clothes and other surroundings

Now, the radiation rate per kilogram is

$\frac{1000\mathrm{W}}{75\mathrm{kg}}=14\mathrm{W}/\mathrm{kg}\text{in case of seen it is}$

$\frac{3.9×{10}^{26}\mathrm{W}}{2×{10}^{30}\mathrm{kg}}=0.0002\mathrm{W}/\mathrm{kg}$

As it is 70,000 times less, have we get a reason that, how is it possible of although the sun is bright it is also very massive. Although it generates energy by nuclear fusion the reaction in its core actually proceeds extremely slowly giving it a ten billion year life time. So, I on the other hand have to replenish my chemical fuel supply on daily basis.