1
JEE Main 2015 (Offline)
+4
-1
A solid body of constant heat capacity $$1$$ $$J/{}^ \circ C$$ is being heated by keeping it in contact with reservoirs in two ways:
$$(i)$$ Sequentially keeping in contact with $$2$$ reservoirs such that each reservoir
$$\,\,\,\,\,\,\,\,$$supplies same amount of heat.
$$(ii)$$ Sequentially keeping in contact with $$8$$ reservoirs such that each reservoir
$$\,\,\,\,\,\,\,\,\,\,$$supplies same amount of heat.
In both the cases body is brought from initial temperature $${100^ \circ }C$$ to final temperature $${200^ \circ }C$$. Entropy change of the body in the two cases respectively is :
A
$$ln2, 2ln2$$
B
$$2ln2, 8ln2$$
C
$$ln2, 4ln2$$
D
$$ln2, ln2$$
2
JEE Main 2015 (Offline)
+4
-1
Consider an ideal gas confined in an isolated closed chamber. As the gas undergoes an adiabatic expansion, the average time of collision between molecules increases as $${V^q},$$ where $$V$$ is the volume of the gas. The value of $$q$$ is: $$\left( {\gamma = {{{C_p}} \over {{C_v}}}} \right)$$
A
$${{\gamma + 1} \over 2}$$
B
$${{\gamma - 1} \over 2}$$
C
$${{3\gamma + 5} \over 6}$$
D
$${{3\gamma - 5} \over 6}$$
3
JEE Main 2015 (Offline)
+4
-1
Consider a spherical shell of radius $$R$$ at temperature $$T$$. The black body radiation inside it can be considered as an ideal gas of photons with internal energy per unit volume $$u = {U \over V}\, \propto \,{T^4}$$ and pressure $$p = {1 \over 3}\left( {{U \over V}} \right)$$ . If the shell now undergoes an adiabatic expansion the relation between $$T$$ and $$R$$ is:
A
$$T\, \propto {1 \over R}$$
B
$$T\, \propto {1 \over {{R^3}}}$$
C
$$T\, \propto \,{e^{ - R}}$$
D
$$T\, \propto \,{e^{ - 3R}}$$
4
JEE Main 2014 (Offline)
+4
-1
Three rods of Copper, Brass and Steel are welded together to form a $$Y$$ shaped structure. Area of cross - section of each rod $$= 4c{m^2}.$$ End of copper rod is maintained at $${100^ \circ }C$$ where as ends of brass and steel are kept at $${0^ \circ }C$$. Lengths of the copper, brass and steel rods are $$46,$$ $$13$$ and $$12$$ $$cms$$ respectively. The rods are thermally insulated from surroundings excepts at ends. Thermal conductivities of copper, brass and steel are $$0.92, 0.26$$ and $$0.12$$ $$CGS$$ units respectively. Rate of heat flow through copper rod is:
A
$$1.2$$ $$cal/s$$
B
$$2.4$$ $$cal/s$$
C
$$4.8$$ $$cal/s$$
D
$$6.0$$ $$cal/s$$
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