PhysicsFlame Institute

22. If 150 J of heat is added to a system and the work done by the system is 110 J, then change in internal energy will be

(a) 260 J (b) 150 J (c) 110 J (d) 40 J Ans. d (7)

21. A perfect gas contained in a cylinder is kept in vacuum. If the cylinder suddenly bursts, then the temperature of the gas

(a) Remains constant (b) Becomes zero (c) Increases (d) Decreases Ans. a (6)

20. In thermodynamic process, 200 Joules of heat is given to a gas and 100 Joules of work is also done on it. The change in internal energy of the gas is

(a) 100 J (b) 300 J (c) 419 J (d) 24 J Ans. b (7)

19. A thermo-dynamical system is changed from

(a) ΔQ (b) ΔW (c) ΔQ + ΔW (d) ΔQ-ΔW Ans. d (6)

18. First law thermodynamics states that

(a) System can do work (b) System has temperature (c) System has pressure (d) Heat is a form of energy Ans. d (7)

17. When the amount of work done is 333 cal and change in internal energy is 167 cal, then the heat supplied is

(a) 166 cal (b) 333 cal (c) 500 cal (d) 400 cal Ans. c (3)

2. The internal energy of an ideal gas depends upon

(a) Specific volume (b) Pressure (c) Temperature (d) Density Ans. c (11)

11. If R = universal gas constant, the amount of heat needed to raise the temperature of 2 mole of an ideal monoatomic gas from 273K to 373K when no work is done

(a) 100 R (b) 150 R (c) 300 R (d) 500 R Ans. c (8)

10. Work done on or by a gas, in general depends upon the

(a) Initial state only (b) Final state only (c) Both initial and final states only (d) Initial state, final state and the path Ans. d (9)

9. A system is given 300 calories of heat and it does 600 joules of work. How much does the internal energy of the system change in this process (J = 4.18 joules/cal)

(a) 654 Joule (b) 156.5 Joule (c) – 300 Joule (d) – 528.2 Joule Ans. a (6)

7. A thermodynamic system goes from states

(i) P1 , V to 2P1 , V (ii) P1, V to P, 2V. Then work done in the two cases is (a) Zero, Zero (b) Zero, PV1 (c) PV1 , Zero (d) PV1, P1 V1 Ans. b (11)

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 (5)

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

(a) Momentum (b) Energy (c) Mass (d) Temperature Ans. b (5)

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 (16)

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 (6)

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 (2)

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 x 10-2J (b) 2 x 10-2j (c) 3 …

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) 12πR2S (d) 36πR2S Ans. a (5)

1. First law of thermnodynamics is given by

(a) dQ = dU + PdV (b) dQ = dU x Pdv (c) dQ = (dU + dv)P (d) dQ = PdU + dV Ans. a (10)

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 (13)

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 (7)

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 J (d) None of these Ans. a (12)

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 : 1 (d) 1 : 2 Ans. b (10)

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 (b) 18.5 μJ (c) 26.8 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 J (c) 2.7×102 J …

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 J,968 m/s (b) 8.78×1021 J,684 m/s (c) 6.21×1021 J,968 m/s …

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 (b) 1.44 x 10-5 Joule (c) 2.88 x 10-5 Joule (d) 5.76 x 10-5 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 (12)

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) 0.057 …

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 (c) 2 x 10-6Nm-1 (d) 2 x 10-8Nm-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 (10)

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 (d) 3.0 J Ans. b (10)

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 (5)

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 sum of the surface areas of both the drops (d) The surface area of the bigger drop is smaller than …