## JEE Main Previous Year Papers Questions With Solutions Physics Heat And Thermodynamics

Multiple Choice with ONE correct answer
1.A constant volume gas thermometer works on  [1980]
a)the principle of Archimedes
b)Boyle’s law
c)Pascal’s law
d)Charle’s law
Ans.(d)

2.A wall has two layers A and B, each made of different material. Both the layers have the same thickness. The thermal conductivity of the material of A is twice that of B. Under thermal equilibrium, the temperature difference across the wall is 36 ° C  The temperature difference across the layer A is  [1980]
a) 6 °C         b) 12 °C
c) 18 °C        d) 24 °C
Ans.

3.An ideal monoatomic gas is taken round the cycle ABCDA as shown in the P-V diagram (see figure). The workdone during the cycle is [1983-1 mark]

a) PV
b)2 PV
c)PV/2
d)Zero
Ans.

4.From the following statements, concerning ideal gas at any given temperature T, select the correct one (s). [1995-2 marks]
a)The co-efficient of volume expansion at constant pressure is the same for all ideal gases
b)The average translational kinetic energy per molecule of oxygen gas is 3kT, k being Boltzmann constant
c)The mean-free path of molecules increases with increase in the pressure
d)In a gaseous mixture, the average translational kinetic energy of the molecules of each component is different
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6.Two metallic sphere S1 and S2are made of the same material and have got identical surface finish. The mass of S1 is thrice that of S2. Both 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 S1 to that of S2 is  [1995-2 marks]

Ans.

7.The average translational kinetic energy and the root mean square speed of molecules in a sample of oxygen gas at 300 K are 6.21 x 10-21J and 484 m/s respectively. The corresponding values at 600 K are nearly (assuming ideal gas behaviour)  [1997-1 mark]
a)12.42 x10-21J,968 m/s
b)8.78 x 10-21  J,684 m/s
c)6.21 x 10-21 J,968 m/s
d)12.42 x  10-21J,684 m/s
Ans.

8.The intensity of radiation emitted by the Sun has its maximum value at a wavelength of 510 nm and that emitted by the North star has the maximum value at 350 nm. If these stars behave like black bodies, then the ratio of the surface temperatures of the Sun and the North Star is [1997-1 mark]
a) 1.46   b) 0.69    c) 1.21   d) 0.83
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9.The average translational kinetic energy of 02  (molar mass 32) molecules at a particular temperature is 0.048 eV. The translational kinetic energy of N2 (molar mass 28) molecules in eV at the same temperature is       [1997-1 mark]
a) 0.0015    b) 0.003    c) 048         d)   0.768
Ans.

10.A vessel contains 1 mole of 02 gas (molar mass  32) at a temperature T. The pressure of the gas is P. An identical vessel containing one mole of He gas (relative molar mass 4) at a temperature 2 T has a pressure of [1997-1 mark]
a) P/8     b) P      c) 2P                 d)   8P
Ans.

11.A spherical black body with a radius of 12 cm  radiates 450 W power at 500 K . If the radius is halved and the temperature doubled, the power radiated in watt would       be   :   [1997-1 mark]
a) 225      b) 450      c) 900             d)       1800
Ans.

12.One mole of a monoatomic gas is heated at a  constant pressure of 1 atmosphere from OK to 100K. If the gas constant R=8.32 J/mol K, the change in internal energy of the gas is approximately    [1998]
a) 2.3J         b) 46J
c) 8.67×103J      d) 1.25xl03J
Ans.

13.An ideal gas heat engine is operating between  227 °C and 127 °C . It absorbs 104J of heat at the higher, temperature. The amount of heat converted into work is [1998]
a) 2000J      b) 4000J       c) 8000J       d)     5600J
Ans.

14.A gas mixture consists of 2 moles of oxygen and  4 moles of argon at temperature T. Neglecting all vibrational modes, the total internal energy of the system is         [1999-2 marks]
a) 4RT      b) 15RT       c) 9RT               d) 11RT
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15.The ratio of the speed of sound in nitrogen gas to that in helium gas, at 300K is [1999-2 marks]

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16.Two monoatomic ideal gases 1 and 2 of molecular  masses M1 and M2 respectively are enclosed in separate containers kept at the same temperature. The ratio of the speed of sound in gas 1 to that in gas 2 is given by   [2000]

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17.A monoatomic ideal gas, initially at temperature T1, is enclosed in a cylinder fitted with a frictionless piston. The gas is allowed to expand adiabatically to a temperature T2 by releasing the piston suddenly. If L3and L2 are the lengths of the gas column before and after expansion respectively, then T1/T2 is given by  [2000-2 marks]

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18.A block of ice at – 10 °C is slowly heated and converted to steam at 100 °C. Which of the following curves represents the phenomen on  qualitatively?[2000-2 marks]

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20.Starting with the same gas expands from volume Vt to V2 in three different ways. The work done by the gas is if the process  is purely isothermal, W2 if purely isobaric and W3 if purely adiabatic. Then   [2000]
a) W2 > W1 > W3      b) W2 > W3 > W1
c) W1 > W2 > W3      d) W1 > W3 > W2
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21.The plots of intensity versus wavelength for three black bodies at temperature Tp T2 and T3 respectively are as shown. Their temperatures are[2000-2 marks]

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22.Three rods made of  same material and having the  same cross-section have been joined as shown in the figure. Each rod is of the same length. The left and right ends are kept at 0 °C and 90 °C respectively. The temperature of the junction of the three rods will be  [2001-2 marks]

a)45 °C
b)60 °C
c)30 °C
d)20 °C
Ans.

23.In a given process on an ideal gas, dW = 0 and  dQ < 0. Then for the gas  [2001]
a)the temperature will decrease.
b)the volume will increase
c)the pressure will remain constant
d)the temperature will increase
Ans.

24.P-V plots for two gases during adiabatic processes are shown in the figure. Plots 1 and 2 should  correspond respectively to  [2001-2 marks]

a)He and Oz
b)02 and He
c)He and Ar
d)02 and N2
Ans.

25.An ideal gas is taken through the cycle A -> B â€”> C â€”>A, as shown in the figure. If the net heat supplied to the gas in the cycle is 5J, the work done by the gas in the process C â€”> A is  [2002-2 marks]

a)-5J
b)-10J
c)-15J
d)-20J
Ans.

26.Which of the following graphs correctly represents the variation of b = -(dV/dP)/V with P for an ideal gas at constant temperature? [2002-2 marks]

Ans.

27.An ideal black body at room temperature is thrown into a furnace. It is observed that  [2002-2 marks]
a)initially it is the darkest body and at later times the brightest.
b)it is the darkest body at all times
c)it cannot be distinguished at all times.
d)initially it is the darkest body and at later times it cannot be distinguished.
Ans.(a) According to Kirchhoff’s law, good absorbers are good emitters and bad reflectors. While at lower temperature, a black-body absorbs all the incident radiations. It does not reflect any radiation inci ­dent upon it when it is thrown in the furnace. Ini ­tially it is therefore the darkest body.
At later times, the black body attains the tempera ­ture of the hot furnace and so it radiates all types of wavelengths with maximum energy. It becomes the brightest of all.Option (a) represents the answer.

28. The graph, shown in the adjacent diagram, represents the variation of temperature (T) of two bodies, x and y having same surface area, with time (t) due to the emission of radiation. Find the correct relation between the emissivite and absorptive powers of the two bodies.

a)Ex > Ey  and ax <ay
b)Ex < Ey  and ax >ay
c)Ex > Ey  and ax >ay
d)Ex <Eyand ax <ay
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Ans.

30.The PT diagram for an ideal gas is shown in the figure, where AC is an adiabatic process. Find the corresponding PV diagram.  [2003-2 marks]

Ans.(b) An inspection of the P-T graph reveals that
1)AC is an adiabatic process (given)
2)AB is an isothermal process a T constant
3)BC is an isobaric process at P constant.
i)In all the four options, BC is an isobaric process
ii)AB is an isothermal process.
.•.pv = constant
Graph between P and V is a rectangular hyper ­bola of the form xy = constant.
Graphs (b) and (d) satisfy this condition Options (a) and (c) are therefore incorrect.
iii)AC is an adiabatic process (given).  In P-V diagram, slope of AC> slope of AB because slope of adiabatic curve > slope of isothermal curve.
This condition is certainly not satisfied in option (d) where AC is a straight line at constant V. Here AC is an isochoric process. It is not an adiabatic process (d) is incorrect.  Hence the ultimate correct process is (b).

31. 2kg of ice at -20 °C is mixed with 5 kg of water at 20 °C in an insulating vessel having a negligible heat capacity. Calculate the final mass of water remaining in the container.It is given that the specific heats of water and ice are 1 kcal/kg °C and 0.5 kcal/kg0C while the latent heat of fusion of ice is 80kcal/kg °C
a)7 kg    b) 6 kg    c) 4 kg    d) 2 kg
Ans.

32.Three discs A, B, and C having radii 2 cm, 4 cm and 6 cm respectively are coated with carbon black on their outer surfaces. The wavelengths corresponding to maximum intensity are 300 nm, 400 nm and 500 nm respectively. The power emitted by them are QA, QB and Qc  [2004-2 marks]
a)Qa will be maximum b) QB will be maximum c) Qc will be maximum d) QA = QB = Qc
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33.If liquefied oxygen at 1 atmospheric pressure is heated from 50 K to 300 K by supplying heat at constant rate, the graph of temperature vs time will be

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34.Two identical rods are connected between two  One of, them is at 100 °C containing water and another is 0 °C containing ice. If rods are connected in parallel then the rate of melting of ice is q1g/sec. If they are connected in series then the rate is q2. The ratio q2/q1  is
a)2   b) 4    c) 1/2   d) 1/4
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35.An ideal-gas initially at P1, V, is expanded to P2, V2  and then compressed adiabatically to the same volume V1 and pressure P3. If W is the net work done by the gas in complete process which of the following is true?               [2004]
a)W>0; P3 > P1   b) W<0; P3>P1
c) W>0; P3<P1     d) W<0;P3<P1
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36.Variation of radiant energy emitted by Sun, filament  of tungsten lamp and welding arc as a function of its wavelength is shown in figure.Which of the following option is the correct match ?             [2005-2 marks]

a)Sun â€”T3  tungsten filamentâ€” T1, welding arc â€”T2
b)Sun-T2, tungsten filamentâ€” T1, welding arcâ€”T3
c)Sun â€”T3, tungsten filament â€”T2, welding arc â€”T3
d)Sun â€”T1, tungsten filamentâ€”T2, welding arcâ€” T1
Ans.

37.In which of the following processes, heat convection does not take place primarly?  [2005-2 marks]
a)land and sea breeze                       b) boiling of water
c)heating air around a furance      d)warming of glass of bulb due to filament.
Ans.(d)Warming of glass of bulb due to filament is due to radiation primarily.  For convection process, a medium is required which can move between two points to transfer heat. Bulb is almost evacuated to have no medium. Option (d) represents the answer.

38.A spherical body of area A and emissivity e = 0.6 is kept inside a perfectly black body. Energy radiated per second by the body at temperature T

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39.Calorie is defined as the amount of heat required to raise temperature of 1 g of water by 1 °C and it is defined under which of the following conditions ?  [2005-2 marks]
a)From 14.5 °C to 15.5 °C at 760 mm of Hg
b)From 98.5 °C to 99.5 °C at 760 mm of H
c)From 13.5 °C to 14.5 °C at 76 mm of Hg
d)From 3.5 °C to 4.5 °C at 76 mm of Hg
Ans.

40.Water of volume 2 litre in a container is heated with a coil of power lkW at 27 °C. The lid of the container is open and energy dissipates at rate of 160 J/s. In how much time temperature will rise from 27 °C to 77 °C. [Given specific heat of water is 4.2 kJ/kg]
a)7 min             b) 6 min 2 s
c) 8 min 20 s     d) 14 min
Ans.

41.An ideal gas is expanding such that PT2 = constant. The coefficient of volume expansion of the gas is[2008]
a)l/T     b) 2/T     c) 3/T    d) 4/T
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42.At room temperature, the rms speed of the  molecules of a certain diatomic gas is found to be 1930 m/s. The gas is                       [1984-2 marks]
a)H2     b) F2     c) 02     d) Cl2
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43.70 calorie of heat are required to raise the  temperatureof 2 mole of an ideal gas at constant pressure from 30 °C to 35 °C.The amount of heat required (in calorie) to raise the temperature of the same gas through the same range (30 °C to 35 °C) at constant volume is                 [1985-2 marks]
a)30    b) 50    c) 70    d) 90
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44.Steam at 100 °C is passed into 1.1 kg of water  contained in a calorimeter of water equivalent 0.02kg at 15 °C till the temperature of the calorimeter and its contents rises at 80 °C.The mass of the steam condensed in kilogram is  [1986-2 marks]
a)0.130    b)0.065    c)0.260    d)0.135
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45.Acylinder of radius R,made of a material of thermal  conductivity K1, is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of a materialof thermal conductivity K2.The two ends of the combined system are maintained at two different temperatures.There is no loss of heat across the cylindrical surface and the system is in steady state.The effective thermal conductivity of the system is [1988-2 marks]
a)K1 + K2                                           b)K1K2(K1 +K2)
c) (K1 +3K2)/4          d) (3K1 +K2)/4
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47.A real gas behaves like an ideal gas if its [2010]
a)pressure and temperature are both high
b)pressure and temperature are both low
c)pressure is high and temperature is low
d)pressure is low and temperature is high
Ans.(d) At low pressure and high temperature, the in ­teraction between molcules approaces to zero. Therefore real gas is behaves as ideal gas.

48.6 liter of helium gas at STP is adiabatically  compressed to 0.7 liter. Taking the initial temperature to be T: , the work done in the process is [2011]

Ans.

Multiple Choice with ONE or More Than ONE correct answers
49.For an ideal gas    [1989-2 marks]
a) the change in internal energy in a constant pressure process from temperature T1  to T2 is equal to nCv (T2 -T1) , where Cv is the molar specific heat at constant volume and n the number of moles of the gas.
b) the change in internal energy of the gas and the work done by the gas are equal in magnitude in an adiabatic process.
c) the internal energy does not change in an isothermal process.
Ans.

50.When an ideal diatomic gas is heated at constant pressure ,the fraction of the heat energy supplied which increases the internal energy of the gas is
a)2/5    b)3/5   c)3/7   d)5/7
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51.Three closed vessels A, B and C are at the same temperature T and contain gases which obey the Maxwellian distribution of velocities.Vessel A contains only 02,B only N2 and C a mixture of equal quantities of 02 and N2. If the average speed of the 02 molecules in vessel A is V1 that of the N2 molecules in vessel B is v2, the average speed of the 02 molecules in vessel C is Where M is the mass of an oxygen molecule [1992-2 marks]

Ans.(b) According to Maxwell’s distribution of speed of gas, the average speed of molecules

52. An  ideal gas is taken from the state A (pressure P, volume V) to the state B(pressure P/2,volume 2V) along a straight line path in the P-V diagram. Select the correct statement (s) from the following.  [1993-2 marks]
a)The workdone by the gas in the process A to B exceeds the work that would be done by it if the system were taken from A to B along the isotherm.
b)In the T-V diagram, the path AB becomes a part of a parabola.
c)In the P-T diagram ,the path AB becomes a part of a hyperbola.
d)In going from A to B ,the temperature j of the gas first increases to a maximum value and then decreases.
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54.The temperature of an ideal gas is increased from  120 K to 480 K. If at 120 K the root -mean square velocity of the gas molecules is v, at 480 K it becomes                   [1996-2 marks]
a) 4v     b) 2v       c) v/2     d) v/4
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56.A given quantity of an ideal gas is at pressure P  and absolute temperature T.The isothermal bulk modulus of the gas is   [1998-2 marks]
a)2|3  p                       b) P          c)3|2  p                                               d)2P
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57.Two cylinders A and B fitted with pistons contain  equal amounts of an ideal diatomic gas at 300 K.The piston of A is free to move,while that of B is held fixed.The same amount of heat is given to the gas in each cylinder.If the rise in temperature of the gas in A is 30K, rise in temperature of the gas in B is     [1998-2 marks]
a) 30K      b) 18 K      c) 50 K     d) 42 K
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58.During the melting of a slab of ice at 273 K at  atmospheric pressure      [1998-2 marks]
a)positive work is done by the ice-water system on the atmosphere
b)positive work is done on the ice-water system by the atmosphere
c)the internal energy of the ice-water system increases.
d)the internal energy of the ice-water system decreases.
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59.A black body is at a temperature of 2880 K. The ‘ energy of radiation emitted by this object with  wavelength between 499 nm and 500 nm is U1, between 999 nm and 1000 nm is U2 and between 1499 nm and 1500 nm is U3. The Wien constant b = 2.88 x 106 nm K. Then [1998-2 marks]
a) U1 = 0                 b) U3 = 0
c) U1 > U2         d) U2 > U1
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61.A vessel contains a mixture of one mole of oxygen and two moles of nitrogen at 300 K. The ratio of the average rotational kinetic energy per 02 molecule to that per N2 molecule is [1998-2 marks]
a)1:1        b) 1:2
c) 2:1      d) depends on the moments of inertia of the two molecules
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62.A bimetallic strip is formed out of two identical strips one of copper and the other of brass. The coefficients of linear expansion of the two metals are ac and aB. On heating, the temperature of the strip goes up by DT and the strip bends to form an arc of radius of curvature R. Then R is :  [1999-3 marks]
a)proportional at DT
b)inversely proportional to DT
c)proportional to |aB – ac|
d)inversely proportional to |aB – ac|
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63.Initially a black body at absolute temperature T is kept inside a closed chamber at absolute temperature T0. Now the chamber is slightly opened to allow Sun rays to enter. It is observed that temperatures T and T0 remains constant. Which of the following statements is/are true?  [2006-5 marks]
a)The rate of emission of energy from the black body remains the same
b)The rate of emission of energy from the black  body increases
c)The rate of absorption of energy by the black bo-‘-y increases.
d)The energy radiated by the black body equals he energy absorbed by it.
Ans.(a,d) From Stefan’s law, the rate of emission of energy from a black body is proportional to            (T-To  )4  Since T and T0  remain constant, the rate of emission of energy remains the same. Since the temperature of the black body remains constant, the energy radiated by it = energy absorbed by it. Hence the correct choices are (a) and (d).

64.One mole of an ideal gas in initial state A undergoes a cyclic process ABCA, as shown in the figure. Its pressure at A is P0. Choice the correct option(s)  from the following. [2010]

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65.Cv and Cp denote the molar specific heat capacities of a gas at constant volume and constant pressure, respectively. Then [2009]
a)Cp – Cv is larger for a diatomic ideal gas than for a mono atomic ideal gas
b)Cp + Cv is larger for a diatomic ideal gas than for a mono atomic ideal gas
c)Cp/Cv is larger for a diatomic ideal gas than for a mono atomic ideal gas
d)Cp . Cv is larger for a diatomic ideal gas than for a mono atomic ideal gas
Ans.

66.The figure shows the P-V plot of an ideal gas taken through a cycle ABCDA. The part ABC is a semi ­circle and CDA is half of an ellipse. Then, [2009]

a)the process during the path A B is isothermal
b)heat flows out of gas during the path B â€”>Câ€”>D
c)work done during the path Aâ€”>Bâ€”>C is zero
d)positive work is done by the gas in the cycle ABCDA
A composite block is made of o il_____________ sl 6l
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67.slabs A, B, C, D and E of h“â€˜ different thermal conduc ­tivities (given in terms of a constant K) and sizes (given in terms of length, L) as shown in the figure. All slabs are of same width. Heat â€˜Q’ flows only from left to right through the blocks. Then in steady state      [2011]

a)heat flow through A and E slabs are same
b)heat flow through slab E is maximum
c)temperature difference across slab E is smallest
d)heat flow through C = heat flow through  B + heat flow through D
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Assertion & Reasoning type
Instructions : The following question contains statement -1 (assertion) and statement -2 (reason) Of these statements, mark correct choice if
a)Statement – 1 and 2 are true and statement-2 is a correct explanation for statement-1
b)Statement – 1 and 2 are true and statement-2 is not a correct explanation for statement-1
c)Statement – 1 is true, statement-2 is flase
d)Statement – 1 is false, statement-2 is true.

68.Statement-1: The total translational kinetic energy of all the molecules of a given mass of an ideal gas is 1.5 times the product of its pressure and its volume. Statement-2: The molecules of a gas collide with each other and the velocities of the molecules change due to the collision [2007-3 marks]
Ans.(b)

Matching Type
69.Heat given to process is positive, match the following option of column I with the corresponding option  option of column II  [2006-6 marks]

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70.Column I gives some devices and column II gives some processes on which the functioning of these devices  depend. Match the device in column I with the processes in column II. [2007-6 marks]

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71.Column I contains a list of processes involving expansion of an ideal gas. Match this with Column II describing the thermodynamic change during this process.

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72.Column II gives certain systems undergoing a process. Column I sugests changes in some of the parameters related to the system. Match the statements in Column I to the appropriate process (es) from Column II. [2009]

Ans.p) When an uncharged capacitor is connected to a battery, it becomes charged and energy is stored in the capacitor.
q) When a gas in an adiabatic container fitted with an adiabatic piston is compressed by pushing the piston then internal energy of the system increases du = dQ – dW = O – ( Pdv) = + Pdv.
Mechanical energy provided to the system (by the moment of the piston) is converted into kE of gas molecules.
r) As the gas in a rigid container gets cooled, the internal energy of the system will decrease. The average KE per molecule will decrease. Hence None of the options in column I matches.
s) When a heavy nucleus initially at rest splits into two nuclei of nearly equal masses and some neutrons are emitted then (i) internal erergy of the system is converted into mechannical energy (ii) mass of the system decreases which converts into energy.
t) When a resistive wire loop is placed in a time varying magnetic field per pendicular to its plane, (i) Induced current shows in the loop due to which the energy of system is increased.

73.One mole of a monatomic ideal gas is taken through a cycle ABCDA as shown in the P.V.diagram. Column II given the characteristics involved in the cycle. Match them with each of the processes given in Column I

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76.A composite rod is made by joining a copper rod, end to end, with a second rod of different material but of the same cross-section. At 25 °C » the composite rod is 1 metre in length, of which the length of the copper rod is 30cm. At 125 °C the length of the composite rod increases by 1.91mm.When the composite rod is not allowed to expand by holding it between two rigid walls, it is found that the length of the two constituents do not change with the rise of temperature. Find the Young’s modulus and the coefficient of linear expansion of the second rod.[Given : Coefficient of linear expansion of copper = 1.7xI0-5per °C,  Young’s modulus of copper 1.3×1011N/m2 ]
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77.A solid material is supplied with  heat at constant rate. The  temperature of the material is changing with the heat input as shown in the graph in figure.Study the graph carefully and answer the following questions.

i)What do the horizontal region AB and CD represent ?
ii)If CD is equal to 2AB, what do you infer?
iii)What does the slope of DE represent?
iv)The slope of OA > the slope of BC. What does  this indicate ?     [1980]
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78.A jar contains a gas and a few drops of water at T K .The pressure in the jar is 830 mm of Hg. The temperature of the jar is reduced by 1%. The saturated vapour pressures of water at the two temperatures are 30 and 25mm of Hg. Calculate the new pressure in the jar. [1980]
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79.A lead bullet just melts when stopped by an  obstacle. Assuming that 25% of the heat is absorbed by the obstacle, find the velocity of the bullet if its initial temperature is 27 °C. (Meltging point of lead = 327 °C. Specific heat of lead = 0.03 cal/g °C, Latent heat of fusion of lead = 6 cal/g, J = 4.2 J/cal.) [1981-3 marks]