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July 2022

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8. If the amount of heat given to a system be 35 joules and the amount of work done by the system be -15 joules, then the change in the internal energy of the system is

(a) -50 joules       (b) 20 joules (c) 30 joules        (d) 50 joules Ans. d (10)

6. The first law of thermodynamics is concerned with the conservation of

(a)  Momentum                       (b)  Energy (c)   Mass                                   (d)  Temperature Ans. b (6)

5. The temperature of an ideal gas is kept constant as it expands. The gas does external work. During this process, the internal energy of the gas

(a)  Decreases (b)  Increases (c)   Remains constant (d)  Depends on the molecular motion Ans. c (22)

4. Heat given to a system is 35 joules and work done by the system is 15 joules. The change in the internal energy of the system will be

(a)  – 50 J                                  (b)  20 J (c)   30 J                                     (d)  50 J Ans. b (9)

3. In changing the state of thermodynamics from A to B state, the heat required is Q and the work done by the system is W. The change in its internal energy is

(a)  Q + W                                 (b)  Q – W (c)   Q                                         (d) (Q – W)/2 Ans. b   (3)

43. A liquid film is formed in a loop of

area 0.05 m2. Increase in its potential energy will be (T = 0.2 N/m)    (a)        5...

41. Radius of a soap bubble is increased from R to 2R work done in this process in terms of surface tension is

(a)      24πR2S                        (b) 48 πR2S (c)   ...

1. First law of thermnodynamics is given by

(a)  dQ = dU + PdV                 (b) dQ = dU x Pdv (c) ...

45. If two soap bubbles of equal radii r coalesce then the radius of curvature of interface between two bubbles will be

(a)  r                                          (b)  0 (c)   Infinity                               (d)  1/2r Ans. c (15)

44. In order to float a ring of area 0.04 m2 in a liquid of surface tension 75 N/m, the required surface energy will be

(a)  3 J                                       (b)  6.5 J (c)  1.5 J                                    (d)  4 J Ans. a (9)

42. The work done in blowing a soap bubble of radius 0.2 m is (the surface tension of soap solution being 0.06 N/m)

(a)     192π  x   10-4 J          (b) 280π  x   10-4 J (c)      200π  x   10-3...

40. Two small drops of mercury, each of radius R, coalesce to form a single large drop. The ratio of the total surface energies before and after the change is

(a)  1:21/3                              (b) 21/3:1 (c)   2...

39. A drop of mercury of radius 2 mm is split into 8 identical droplets. Find

the increase in surface energy. (Surface tension of mercury is 0.465 J/m2 ) (a)    23.4 μJ       ...

27. The kinetic energy of one gram molecule of a gas at normal temperature and pressure is(8.31 J/mole-K)

(a) 0.56×104 J                                 (b) 1.3×102...

35. The average translational energy and the m.s. speed of molecules in a sample of oxygen gas at 300 K are

6.21×10-21  J and 484 m/s respectively. The corresponding values at 600 K are nearly (assuming ideal gas behaviour) (a) 12.42×1021 ...

38. A film of water is formed between two straight parallel wires of length 10cm each separated by 0.5 cm. If their separation is increased by 1 mm while still maintaining their parallelism,

how much work will have to be done (Surface tension of water =7.2 x10-2 N/m) (a) 7.2 x 10-6 Joule ...

37. When two small bubbles join to form a bigger one, energy is

(a)  Released                            (b)  Absorbed (c)   Both (a) and (b)               (d)  None of these Ans. a (13)

36. A mercury drop of radius 1cm is sprayed into

108 drops of equal size. The energy expended in joules is (surface tension of Mercury is 460 x 10-3N/m (a) ...

35. If work done in increasing the size of a soap film from to is then the surface tension is

(a) 2 x 10-2Nm-1                          (b) 2 x 10-4Nm-1...

34. 8 mercury drops coalesce to form one mercury drop, the energy changes by a factor of

(a)  1                                         (b)  2 (c)   4                                         (d)  6 Ans. c (13)

33. The surface energy of liquid film on

a ring of area  is (Surface tension of liquid   = 5Nm-1) (a) 0.75 J                                         (b)  1.5 J (c)   2.25 J                                ...

32. 8000 identical water drops are combined to form a big drop. Then the ratio of the final surface energy to the initial surface energy of all the drops together is

(a)  1 : 10                                  (b)  1 : 15 (c)   1 : 20                                  (d)  1 : 25 Ans. c (7)

31. Which of the following statements are true in case when two water drops coalesce and make a bigger drop

(a)  Energy is released (b)  Energy is absorbed (c)   The surface area of the bigger drop is greater than the...

45. The average kinetic energy of a helium atom 30° C at

(a)  Less than 1 eV                   (b)  A few keV (c)   50-60 eV                            (d)  13.6 eV Answer-a (13)

44. The temperature of a gas is – 68°C. At what temperature will the average kinetic energy of its molecules be twice that of at – 68°C

(a)  137°C                                (b)  127°C (c)   100°C                                (d)  105°C Answer-a (10)

43. On absolute temperature, the kinetic energy of the molecules

(a)  Becomes zero                    (b)  Becomes maximum (c)   Becomes minimum          (d)  Remains constant Answer-a (14)

42. Energy of all molecules of a monoatomic gas having a volume V and pressure P is (3/2)PV . The total translational kinetic energy of all molecules of a diatomic gas as the same volume and pressure is

(a) (1/2)PV                                   (b)...

41. Vessel A is filled with hydrogen while vessel B, whose volume is twice that of A, is filled with the same mass of oxygen at the same temperature. The ratio of the mean kinetic energies of hydrogen and oxygen is

(a)  16 : 1                                  (b)  1 : 8 (c)   8 : 1                                    (d)  1 : 1 Answer-d (40)

40. If temperature of gas increases from 27°C to 927°C the K.E. will be

(a)  Double                                 (b)  Half (c)  ...

39. A box contains a mixture of

H2 and He gases. Which of the following statements are corrects (a)  The average translational kinetic energies of H2  molecules...

38. At the same temperature and pressure and volume of two gases, which of the following quantities is constant

(a)  Total number of molecules (b)  Average kinetic energy (c)   Root mean square velocity (d)  Mean free path Answer-b (14)

37. At 0 K which of the following properties of a gas will be zero

(a) Kinetic energy                          (b)  Potential energy (c)   Vibrational energy                (d)  Density Answer-a (6)

36. A polyatomic gas with n degrees of freedom has a mean energy per molecule given by

(a)  (nkT)/N                                     ...

34. The average translational kinetic energy of

O2 (molar mass 32) molecules at a particular temperature is 0.048 eV. The translational kinetic energy of N2  (molar mass...

33. The average kinetic energy of a gas molecule at 27°C is

6.21×10-21 J . Its average kinetic energy at 227°C will be (a) 52.2×10-21 J               ...

32. At 27°C temperature, the kinetic energy of an ideal gas is

E1 . If the temperature is increased to 327°C, then kinetic energy would be (a)  2E1         ...

31. The translational kinetic energy of gas molecule for one mole of the gas is equal to

(a) (3/2)RT                                     ...

30. Read the given statements and decide which is/are correct on the basis of kinetic theory of gases [MP PMT 2003] (I) Energy of one molecule at absolute temperature is zero (II) r.m.s. speeds of different gases are same at same temperature (III) For one gram of all ideal gas kinetic energy is same at same temperature (IV) For one mole of all ideal gases mean kinetic energy is same at same temperature

(a)  All are correct                           (b)  I and IV are correct (c)   IV is correct             ...

29. At what temperature is the kinetic energy of a gas molecule double that of its value of 27°C

(a)  54°C                                          (b)  300 K (c)   327°C                           ...

28. The mean kinetic energy of a gas at 300 K is 100 J. The mean energy of the gas at 450 K is equal to

(a)   100 J                                          (b)  3000 J (c)   450 J                       ...

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