1.
If the temperature of the sun were to increase from $$T$$ to $$2\,T$$ and its radius from $$R$$ to $$2\,R,$$ then the ratio of the radiant energy received on earth to what it was previously will be
2.
According to Newton’s law of cooling, the rate of cooling of a body is proportional to $${\left( {\Delta \theta } \right)^n},$$ where $${\Delta \theta }$$ is the difference of the temperature of the body and the surroundings, and $$n$$ is equal to
3.
Two metallic spheres $${S_1}$$ and $${S_2}$$ are made of the same material and have got identical surface finish. The mass of $${S_1}$$ is thrice that of $${S_2}.$$ Both the spheres are heated to the same high temperature and placed in the same room having lower temperature but are thermally insulated from each other. The ratio of the initial rate of cooling of $${S_1}$$ to that of $${S_2}$$ is
A.
$$\frac{1}{3}$$
B.
$${\frac{1}{{\sqrt 3 }}}$$
C.
$${\frac{{\sqrt 3 }}{1}}$$
D.
$${\left( {\frac{1}{3}} \right)^{\frac{1}{3}}}$$
4.
A black body at $${1227^ \circ }C$$ emits radiations with maximum intensity at a wavelength of $$5000\,\mathop A\limits^ \circ .$$ If the temperature of the body is increased by $${1000^ \circ }C,$$ the maximum intensity will be observed at
According to Wien's law
$${\lambda _m}T = {\text{constant}}\left( {{\text{say}}\,b} \right)$$
where, $${\lambda _m}$$ wavelength corresponding to maximum intensity of radiation and $$T$$ is temperatures of the body in kelvin.
So for two different cases i.e. at two different temperature of body
$$\therefore \frac{{{{\lambda '}_{m'}}}}{{{\lambda _m}}} = \frac{T}{{T'}}$$
Given, $$T = 1227 + 273 = 1500\,K,$$
$$\eqalign{
& T' = 1227 + 1000 + 273 = 2500\,K \cr
& {\lambda _m} = 5000\mathop A\limits^ \circ \cr} $$
Hence, $${{\lambda '}_m} = \frac{{1500}}{{2500}} \times 5000 = 3000\mathop A\limits^ \circ $$
5.
Parallel rays of light of intensity $$I = 912\,W\,{m^{ - 2}}$$ are incident on a spherical black body kept in surroundings of temperature $$300\,K.$$ Take Stefan-Boltzmann constant $$\sigma = 5.7 \times {10^{ - 8}}\,W\,{m^{ - 2}}{K^{ - 4}}$$ and assume that the energy exchange with the surroundings is only through radiation. The final steady state temperature of the black body is close to
7.
Consider two hot bodies $${B_1}$$ and $${B_2}$$ which have temperatures $${100^ \circ }C$$ and $${80^ \circ }C$$ respectively at $$t = 0.$$ The temperature of the surroundings is $${40^ \circ }C.$$ The ratio of the respective rates of cooling $${R_1}$$ and $${R_2}$$ of these two bodies at $$t = 0$$ will be
According to Wien’s displacement law, the quantity of energy radiated out by a body is not uniformly distributed over all the wavelengths emitted by it. It is maximum for a particular wavelength $$\left( \lambda \right),$$ which is different at different temperatures. As the temperature is increased, the value of the wavelength which carries maximum energy is decreased.
The statement of this law is as follows
“The wavelength corresponding to maximum energy is inversely proportional to the absolute temperature of the body.”
i.e. $${\lambda _m} \propto \frac{1}{T}\,\,{\text{or}}\,\,{\lambda _m}T = {\text{constant}}$$
9.
A black body is at a temperature of $$5760\,K.$$ The energy of radiation emitted by the body at wavelength $$250\,nm$$ is $${U_1},$$ at wavelength $$500\,nm$$ is $${U_2}$$ and that at $$1000\,nm$$ is $${U_3}.$$ Wien’s constant, $$b = 2.88 \times {10^6}nmK.$$ Which of the following is correct?
Given, temperature, $${T_1} = 5760\,K$$
Since, it is given that energy of radiation emitted by the body at wavelength $$250\,nm$$ in $${U_1},$$ at wavelength $$500\,nm$$ is $${U_2}$$ and that at $$1000\,nm$$ is $${U_3}.$$
$$\because $$ According to Wien’s law, we get $${\lambda _m}T = b$$
where, $$b =$$ Wien’s constant $$ = 2.88 \times {10^6}nmK$$
$$\eqalign{
& \Rightarrow {\lambda _m} = \frac{b}{T} \cr
& \Rightarrow {\lambda _m} = \frac{{2.88 \times {{10}^6}nmK}}{{5760\,K}} \cr
& \Rightarrow {\lambda _m} = 500\,nm \cr} $$
$$\therefore {\lambda _m} = $$ wavelength corresponding to maximum energy, so, $${U_2} > {U_1}.$$
10.
A liquid in a beaker has temperature $$\theta \left( t \right)$$ at time $$t$$ and $${{\theta _0}}$$ is temperature of surroundings, then according to Newton's law of cooling the correct graph between $${\log _e}\left( {\theta - {\theta _0}} \right)$$ and $$t$$ is: