Answers posted by yamini.v

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The temperature of a solid falls from $\;72^{0}C\;$ to $\;60^{0}C\;$ in 10 minutes . How much time will it take to cool from $\;60^{0}C\;$ to $\;52^{0}C\;$ if the temperature of surroundings is $\;36^{0}C\;$ c ?

answered Apr 8, 2014

Answer : $\;15 \;min$Explanation :$\large\frac{dT}{dt} = K (\large\frac{\theta_{1}+\theta_{2}}{2}...

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A copper rod AB of length 100 cm is fixed with a steel rod BC of length 20 cm at B . If the ends A and C are maintained at temperature $\;100^{0}C\;$ and $\;0^{0}C\;$ , then the temperature of the function B is : [thermal conductivities of copper and steel are 0.9 and 0.18 CGS units respectively ]

answered Apr 8, 2014

Answer : $\;50^{0}C$Explanation :Rate of heat flow is the same $\large\frac{K_{1}A(T_{1}-\theta)}{...

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A cylinder of radius r and thermal conductivity $\;K_{1}\;$ is surrounded by cylindrical shell of inner radius r and outer radius 2r and thermal conductivity $\;K_{2}\;$ . The effective thermal conductivity when ends of combined system $\;t_{1}\;$ and $\;t_{2}\;$ under steady state is

answered Mar 31, 2014

Answer : $\;(\large\frac{K_{1}+3K_{2}}{4})$Explanation :$\large\frac{dQ}{dt} = \large\frac{K_{1} (...

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For hydrogen gas $\;C_{p}-C_{v} =a\;$ and for oxygen $\;C_{p}-C_{v}=b\;$ . Then the relation between a and b is given by

answered Mar 31, 2014

Answer : $\;a=b$Since $C_p - C_v = R \rightarrow a = b$

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Helium gas is filled vessel ( having negligible thermal expansion coefficeint ) when heated from 300 K to 600 K . Then the average kinetic energy of atom will be

answered Mar 31, 2014

Answer : Twice the original valueExplanation :$KE_{average} = \large\frac{3}{2} $$KT\;$ for a single...

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At what temperature the molecule of nitrogen will have the same rms velocity as the molecule of oxygen at $\;127^{0}C\;$ ?

answered Mar 31, 2014

Answer : $\;457^{0}C$Explanation :$V_{m}=\sqrt{\large\frac{3RT}{M}}$$\large\frac{V_{N_{2}}}{V_{O_{...

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At room temperature , the rms speed of the molecules of a diatomic gas is found to be 1933 m/s . The gas is

answered Mar 31, 2014

Answer : $\;H_{2}$Explanation :$V_{rms} = \sqrt{\large\frac{3RT}{M}}$or $\;M=\large\frac{3RT}{V_{r...

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A gas mixture consists of 2 mol of oxygen and 4 moles of Argon at temperature T . Neglecting all vibrational moles , the total internal energy of the system is

answered Mar 31, 2014

Answer : $\;11\;RT$Explanation :$U= \large\frac{n_{1}f_{1}}{2}$$RT + \large\frac{n_{2}f_{2}}{2} $$R...

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If 2 moles of diatomic gas and 1 mole of monoatomic gas are mixed , then ratio of specific heats $\;\large\frac{C_{p}}{C_{v}}\;$ is

answered Mar 27, 2014

Answer : $\;\large\frac{19}{13}$Explanation :$C_{peq} = \large\frac{n_{1}C_{p_{1} }+ n_{2} C_{p_{...

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A monoatomic gas expands at constant pressure on heating . The percentage of heat supplied used for external work is

answered Mar 27, 2014

Answer: 40%For an isobaric process, $Q = nC_P \Delta T$ and $W = nR \Delta T$Now, $C_P = \large\frac...

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A gas is heated at constant pressure . The fraction of heat supplied used for external work expressed in terms of the adiabatic index is

answered Mar 27, 2014

Answer: $\large\frac{\gamma -1}{\gamma}$For an isobaric process, $Q = nC_P \Delta T$ and $W = nR \De...

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The number of particles in a cubic millimeter of a gas at temperature 273 K and 1.00 atm pressure is

answered Mar 27, 2014

Answer : 2.69 $\times$ 10$^{16}$$PV = nRT \rightarrow n = \large\frac{PV}{RT}$Number of particles $ ...

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A closed vessel contains 8 g of oxygen and 7 g of nitrogen . The total pressure is 10 atm at a given temperature . If now oxygen is absorbed by introducing a suitable absorbent , the pressure of the remaining gas is atm will be

answered Mar 27, 2014

Answer : 5Explanation :By Dalton's law of partial pressures $p = (n_{1}+n_{2}) \large\frac{RT}{V}$$...

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Calculate the temperature if helium atoms have an rms speed equal to the escape velocity from the surface of the Earth (11.2km/s)?

answered Mar 27, 2014

Answer : 2.01 $ \times$ 10$^{4}$ K$v_{rms} =\sqrt{ \large\frac{ 3RT}{M}}$$ = 11.2 \times 10^3\; m/...

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Three closed vessels A , B and C are at the same temperature T and contain gases which obey maxwellian distibution of velocities . Vessel A contains only $\;O_{2}\;$ . B only $\;N_{2}\;$ and C a mixture of equal quantities of $\;O_{2}\;$ and $\;N_{2}\;$ . If the average speed of $\;O_{2}\;$ molecules in vessel A is $\;V_{1}\;$ , that of $\;N_{2}\;$ molecules in vessel B is $\;V_{2}\;$ the average speed of the $\;O_{2}\;$ molecules in vessel C will be

answered Mar 27, 2014

Answer : $\;V_{1}$Explanation :So the answer is $\;V_{1}\;$

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Consider a mixture of oxygen and hydrogen kept at room temperature . As compared to a hydrogen molecule , an oxygen molecule hits the wall

answered Mar 27, 2014

Answer : with smaller average speedExplanation :$V_{av} = \sqrt{\large\frac{8RT}{\pi M}}$$M_{O_{2}}...

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The rms speed of oxygen molecules in a gas is V . If the temperature is doubled and the $\;O_{2}\;$ molecule dissociates into oxygen atoms , the rms speed will become

answered Mar 27, 2014

Answer : $\;2V$Explanation :$V_{rms} = \sqrt{\large\frac{3RT}{M}}$$V_{rms}^{'} = \sqrt{\large\frac{...

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Suppose a container is evaluated to leave first one molecule of a gas in it . Let $\;V_{a}\;$ and $\;V_{rms}\;$ represents the average speed and the rms speed of the gas .

answered Mar 27, 2014

Answer : $\;V_{a} = V_{rms}$Explanation :Conceptual

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Figure shows graphs of pressure Vs density for an ideal gas at two temperatures $\;T_{1}\;$ and $\;T_{2}\;$

answered Mar 27, 2014

Answer : $\;T_{1} > T_{2}$Explanation :$\large\frac{p}{\rho} = constant = \large\frac{3RT}{M}\;$ ...

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The temperature at which the r.m.s. velocity of oxygen molecules equal that of nitrogen molecules at $\;100^{0}C\;$ is nearly :

answered Mar 26, 2014

Answer : $\;426.3K$Explanation :$\sqrt{\large\frac{3RT_{1}}{M_{1}}}=\sqrt{\large\frac{3RT_{2}}{M_{2...

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Which of the following quantities is zero on an average for the molecules of an ideal gas in equilibrium ?

answered Mar 26, 2014

Answer : momentumExplanation : At equilibrium, the momentum is conserved and hence zero.

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Which of the following is correct for the molecules of a gas in thermal equilibrium ?

answered Mar 26, 2014

Answer : They have a certain constant average speed.Explanation :$V_{av}=\sqrt{\large\frac{8KT}{\pi...

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If the temperature of a body is raised by $\;5 \%\;$ . Find increase in radiated energy .

answered Mar 26, 2014

Answer : $\;20\%$Explanation :$U/second=\sigma A T^{4}$$\large\frac{\bigtriangleup u}{u}= 4\large\...

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Find the temperature at which a black body radiates energy at the rate of $\;5.67\;W/cm^{2}\;$

answered Mar 26, 2014

Answer : $\;10^{3}K$Explanation :By stefan's law energy radiated per second / unit area = $\; \sigm...

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Two spheres of same material and radii 4 m and 1 m at temperature 1000 K and 2000 K . Find the ratio of the energies radiated by them in one second .

answered Mar 26, 2014

Answer : $ \;1 : 1$Explanation :$\large\frac{stefan's\;law}{energy\;radiated\;per\;second}\;U_{4}=...

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The maximum emission wavelength at temperature 2000 K is $\;4 \mu m\;$ . The maximum wavelength corresponding to temperature 2400 K will be

answered Mar 26, 2014

Answer : $\; 3.33 \times 10^{-6} \;m$Explanation :$\lambda m T = constant\;\;$ (wein's displacement...

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Two identical rods A and B when joined in series conduct heat at a rate of 4 w at steady state . If they are connected in parallel , they conduct heat at rate of

answered Mar 25, 2014

Answer : $\;16\;W$Explanation :In series $\;Q_{1}=\large\frac{KA(T_{1}-T_{2})}{2L}$In parallel $Q_{...

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The ends of a metal rod of length 60 cm are showing the steady temperature $\;70^{0}C\;$ and $\;30^{0}C\;$ is the steady state . The temperature of the rod at a distance of 15 cm from hot end is

answered Mar 25, 2014

Answer : $\;60^{0}C$Explanation :$\large\frac{70-30}{60} = \large\frac{70-X}{15}$$X=60^{0}C$

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Five rods of the same dimension are arranged as shown . AB are maintained at different temperatures . No Heat flows through the central rod ; then

answered Mar 25, 2014

Answer : $\;K_{1}K_{2}=K_{3}K_{4}$Explanation :Since no heat flows through the central rod , temper...

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Two metal rods have their thermal conductivities $\;K_{1}\;$ and $\;K_{2}\;$ in the ratio 3 : 2 so that their thermal resistance are the same . Then their lengths are is the ratio ( Area of C .S . are the same )

answered Mar 25, 2014

Answer : $3 : 2$Explanation :Thermal resistance = $\;\large\frac{L}{KA}$$\large\frac{L_{1}}{K_{1}A...

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A square iron plate of side 3 cm and thickness 8 mm has its opposite faces at $\;100^{0}C\;$ and $\;60^{0}C\;$ . If K=0.16 C.G.S units , then the amount of heat flow through the rod is 1 minute is

answered Mar 25, 2014

Answer : 4320 calExplanation :$\large\frac{dQ}{dt}= \large\frac{KA (T_{1}-T_{2})}{L}$$=\large\frac...

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The temperature gradient in a rod 0.5 m long is 80 c/m . The temperature of the hot end of the rod is $\;30^{0}C\;$. Then the temperature of the cooler and is

answered Mar 24, 2014

Answer : $\;-10^{0}C$Explanation :$\large\frac{T_{H}-T_{C}}{L}=\large\frac{\bigtriangleup T}{L}$$80...

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Brass at $\;30^{0}C\;$ is observed to be 1 m long when measured by a steel scale which is connect at $\;0^{0}C\;$ . Correct length of the brass of at $\;0^{0}C\;$ is $\;(\alpha_{steel}=12 \times 10^{-6}/^{0}C\;and \; \alpha_{brass}=18 \times 10^{-6}/^{0}C\;)$

answered Mar 24, 2014

Answer : $\;99.98\;cm$Explanation :Correct length of brass at $\;30^{0}C\;$ = length at $\;0^{0}C\;...

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A clock which keeps correct time at $\;20^{0}C\;$ . How many seconds will it gains or loss per day when the temperature falls to $\;0^{0}C\;$ ? ( Coefficient of linear expansion of brass = $\;12\times 10^{-6}/^{0}C\;$ )

answered Mar 24, 2014

Answer : $\;10.36\;sec$Explanation :Time lost or gained per second = $\;\large\frac{1}{2}\;\alpha ...

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An iron bar is heated from $\;0^{0}C\;$ to $\;50^{0}C\;$ . If $\;\gamma\;$ of iron = $\;2 \times 10^{12} \;dyne/cm^{2}\;$ and $\;\alpha\;$ of iron is $\;12 \times 10^{-6}/^{0}C\;$ . The stress developed in the rod if it is prevented from expanding is

answered Mar 24, 2014

Answer : $\;12 \times 10^{7}\;N/m^2$Explanation :$\bigtriangleup l = l \alpha \bigtriangleup t$$st...

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A crystal has a coefficient of linear expansion $\;13\times 10^{-7}/^{0}C\;$ , $\;12 \times 10^{-7}/^{0}C\;$ and $\;10 \times 10^{-7}/^{0}C\;$ in three mutually perpendicular directions respectively . Then the coefficient of cubical expansion of the crystal is

answered Mar 24, 2014

Answer : $\;35\times 10^{-7}/^{0}C$Explanation :$\gamma = \alpha_{1} + \alpha_{2} + \alpha_{3}$$=3...

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The coefficient of linear expansion of a rod changes from $\;\alpha_{1}\;$ to $\;\alpha_{2}\;$ from end to end for a length l of the rod . If the temperature changes from $\;0^{0}C\;$ to $\;t^{0}C\;$ , the change of length is

answered Mar 24, 2014

Answer : $\;\large\frac{(\alpha_{1}+\alpha_{2})}{2}\;lt$Explanation :$\alpha\;$ at a distance x fro...

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A glass bottle weighs 50 g 1040 g then filled with a liquid at $\;0^{0}C\;$ . When it is at $\;100^{0}C\;$ , 10 g of the liquid overflows . If $\;\gamma_{r}=2 \times 10^{-4}/^{0}C\;$ , find the coefficient of linear expansion of container .

answered Mar 24, 2014

Answer : $\;\large\frac{1}{3}\times 10^{-4}/^{0}C$Explanation :Weight of liquid = 990 g$\gamma_{A} ...

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Two identical tumblers are fully filled with water at a certain temperature . One of the tumbler is warmed up and the other cooled . But it is formed that water overflows from both the tumblers . The temperature at which they are fully filled is

answered Mar 24, 2014

Answer : $\;277\;K$ Explanation :$277\;K=4^{0}C$Water expands when heated above $\;4^{0}C\;$ an...

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The mercury column of height $\;0.8\;gm\;$ at $\;0^{0}C\;$ balances the mercury column of height $\;0.8144\;m\;$ at $\;100^{0}C\;$ . Calculate the coefficient of real expansion of mercury ?

answered Mar 24, 2014

Answer : $\;0.00018/^{0}C$Explanation :When 2 liquid columns balance each other , the processes exe...

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When 52 g of liquid in a vessel is heated from $\;0^{0}C\;$ to $\;100^{0}C\;$ 2 g of liquid is expelled . If 104 g of liquid is taken in a vessel made of same matenal how much of liquid is expelled on heating from $\;0^{0}C\;$ to $\;100^{0}C\;$ ?

answered Mar 24, 2014

Answer : $\;4\;g$Explanation :$r= \large\frac{weight\;of\;liquid\;expelled}{weight\;of\;remaining...

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Coefficient of real expansion of mercury is $\;0.18\times 10^{-3}/^{0}C\;$ . If the density of mercury at $\;0^{0}C\;$ is $\;13.6\;gm/C.C\;$ , then is density at 473 K will be

answered Mar 24, 2014

Answer : $\;13.11\;g/C.C$Explanation :$\rho = \large\frac{\rho_{0}}{(1+r_{0}t)}$$=\large\frac{13.6}...

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On heating a liquid of efficient of cubical expansion ' r ' in a container having coefficient of cubical expansion $\;\large\frac{r}{3}\;$ , the level of liquid in the container will

answered Mar 24, 2014

Answer : riseExplanation :Since expansion of liquid is more than expansion of container .

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A mercury thermometer is transferred from melting ice to hot liquid . The mercury rises $\;\large\frac{9}{10}\;$ of the distance between the lower fixed point and the upper fixed point . The temperature of the liquid is $\;^{0}C\;$ is

answered Mar 24, 2014

Answer : $\;90^{0}C$Explanation :$t=\large\frac{9}{10} \;[100-0]=90^{0}C$

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A thermometer which has upper fixed points and lower fixed points equal to $\;95^{0}\;$ and $\;5^{0}\;$ respectively , reads $\;59^{0}\;$. What is the temperature on the centigrade scale .

answered Mar 24, 2014

Answer : $\;60^{\circ}C$Explanation :$\large\frac{\text{Temperature-lower fixed point}}{\text{upper...

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At what temperature is reading on kelvin scale be double that on the celsius scale

answered Mar 21, 2014

Answer : $\;546\;K$Explanation : $K-273=C$$K=C+273=2C$$C=273^{0}C\;,K=546 K$

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Normal body temperature is $\;98.4^{0}F\;.\;$ What is the corresponding reading on the celsius scale ?

answered Mar 21, 2014

Answer : $\;37^{0}C$Explanation :$C=\large\frac{5}{9}\;(F-32)$$=\large\frac{5}{9}\;[98.4-32] \appro...

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The work done in process ABC (in atm litre)

answered Mar 21, 2014

Answer : $\;\large\frac{\pi}{2}$Explanation :Work done = $\;\large\frac{1}{2}\;$ Area of ellipse$...

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A gas is expanded from volume $\;V_{0}\;$ to $\;2V_{0}\;$ under three different processes . Process 1 is isobaric , process 2 is isothermal and process 3 is adiabatic . Let $\;\bigtriangleup u_{1}\;, \bigtriangleup u_{2}\;$ and $\;\bigtriangleup u_{3}\;$ be the change in internal energy of the gas in the three processes . Then :

answered Mar 21, 2014

Answer : $\;\bigtriangleup u_{1} > \bigtriangleup u_{2} > \bigtriangleup u_{3}$Explanation :...

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Work done by gas in cyclic process ABCDA .

answered Mar 21, 2014

Answer : $\;zero$Explanation :https://clay6.com/mpaimg/1_figure18.PNGABOA is a clockwise processWo...

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