PhysicsFlame Institute

7. Assertion : The angle of contact of a liquid decrease with increase in temperature. Reason : With increase in temperature, the surface tension of liquid increase.

Read the assertion and reason carefully to mark the correct option out of the options given below: (a) If both assertion and reason are true and the reason is the correct explanation of the assertion. (b) If both assertion and …

6. Assertion : The impurities always decrease the surface tension of a liquid. Reason : The change in surface tension of the liquid depends upon the degree of contamination of the impurity.

5. Assertion : A large force is required to draw apart normally two glass plate5. Assertion : A large force is required to draw apart normally two glass plates enclosing a thin water film. Reason : Water works as glue and sticks two glass plates. s enclosing a thin water film. Reason : Water works as glue and sticks two glass plates.

46. Surface tension may be defined as

(a) The work done per unit area in increasing the surface area of a liquid under isothermal condition (b) The work done per unit area in increasing the surface area of a liquid under adiabatic condition (c) The work done …

45. The force required to take away a flat circular plate of radius 2 cm from the surface of water, will be (the surface tension of water is 70 dyne/cm)

(a) 280 π dyne (b) 250 π dyne (c) 140 π dyne (d) 210 π dyne Ans. a (37)

2. Assertion : Spring balances show correct readings even after they had been used for a long time interval. Reason : On using for long time, spring balances losses its elastic strength.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. (b) If both assertion and reason are true but reason is not the correct explanation of the assertion. (c) If assertion is …

10. Assertion : Young’s modulus for a perfectly plastic body is zero. Reason : For a perfectly plastic body, restoring force is zero.

9. Assertion : Two identical solid balls, one of ivory and the other of wet-clay are dropped from the same height on the floor. Both the balls will rise to same height after bouncing. Reason : Ivory and wet-clay have same elasticity.

8. Assertion : The bridges declared unsafe after a long use. Reason : Elastic strength of bridges losses with time.

7. Assertion : Strain is a unitless quantity. Reason : Strain is equivalent to force.

6. Assertion : Bulk modulus of elasticity (K) represents incompressibility of the material. Reason : Bulk modulus of elasticity is proportional to change in pressure.

5. Assertion : A hollow shaft is found to be stronger than a solid shaft made of same material. Reason : The torque required to produce a given twist in hollow cylinder is greater than that required to twist a solid cylinder of same size and material.

4. Assertion : Glassy solids have sharp melting point. Reason : The bonds between the atoms of glassy solids get broken at the same temperature.

3. Assertion : Steel is more elastic than rubber. Reason : Under given deforming force, steel is deformed less than rubber.

1. Assertion : The stretching of a coil is determined by its shear modulus. Reason : Shear modulus change only shape of a body keeping its dimensions unchanged.

44. A thread is tied slightly loose to a wire frame as in figure and the frame is dipped into a soap solution and taken out. The frame is completely covered with the film. When the portion A punctured with a pin, the thread.

(a) Becomes concave toward A (b) Becomes convex towards A (c) Remains in the initial position (d) Either (a) or (b) depending on the size of A w.r.t. B Ans. a (15)

43. A wooden stick 2m long is floating on the surface of water. The surface tension of water 0.07 N/m. By putting soap solution on one side of the sticks the surface tension is reduced to 0.06 N/m. The net force on the stick will

(a) 0.07 N (b) 0.06 N (c) 0.01 N (d) 0.02 N Ans. d (11)

42. The dimensions of surface tension are

(a) MLT-1 (b) ML2 T-2 (c) ML0 T-2 (d) ML-1T-2 Ans. c (9)

41. The property utilized in the manufacture of lead shots is

(a) Specific weight of liquid lead (b) Specific gravity of liquid lead (c) Compressibility of liquid lead (d) Surface tension of liquid lead Ans. d (6)

40. Cohesive force is experienced between

(a) Magnetic substances (b) Molecules of different substances (c) Molecules of same substances (d) None of these Ans. (c) The cohesive force is the force of attraction between the molecules of same substance (15)

39. Oil spreads over the surface of water whereas water does not spread over the surface of the oil, due to

(a) Surface tension of water is very high (b) Surface tension of water is very low (c) Viscosity of oil is high (d) Viscosity of water is high Ans. a (58)

38. The force required to separate two glass plates of area

The force required to separate two glass plates of area 10-2m2 with a film of water 0.05 mm thick between them, is (Surface tension of water is 70 x 10-3 N/m) (a) 28 N (b) 14 N (c) 50 N …

37. Due to which property of water, tiny particles of camphor dance on the surface of water

(a) Viscosity (b) Surface tension (c) Weight (d) Floating force Ans. b (12)

36. It is easy to wash clothes in hot water because its

(a) Surface tension is more (b) Surface tension is less (c) Consumes less soap (d) None of these Ans. (b) Surface tension of water decrease with rise in temperature. (9)

35. A 10 cm long wire is placed horizontally on the

A 10 cm long wire is placed horizontally on the surface of water and is gently pulled up with a force of 2 ×10-2 N to keep the wire in equilibrium. The surface tension, in Nm-1, of water is (a) …

34. A thin metal disc of radius r floats on water surface and bends the surface downwards along the perimeter making an angle θ with vertical edge of the disc. If the disc displaces a weight of water W and surface tension of water is T, then the weight of metal disc is

(a) 2πrT + W (b) 2πrT COSθ – W (c) 2πrT COSθ +W (d) W-2πrT COSθ Ans. c (11)

33. Small liquid drops assume spherical shape because

(a) Atmospheric pressure exerts a force on a liquid drop (b) Volume of a spherical drop is minimum (c) Gravitational force acts upon the drop (d) Liquid tends to have the minimum surface area due to surface tension Ans. (d) …

32. Two pieces of glass plate one upon the other with a little water in between them cannot be separated easily because of

(a) Inertia (b) Pressure (c) Surface tension (d) Viscosity Ans. (c) Surface tension pulls the plates towards each other. (6)

8. An elastic material of Young’s modulus Y is subjected to a stress S. The elastic energy stored per unit volume of the material is

(a) 2Y/S2 (b) S2/2Y (c) S/2Y …

7.A particle of mass m is under the influence of a force F which varies with the displacement x according to the relation

A particle of mass m is under the influence of a force F which varies with the displacement x according to the relation F= -kx+Fº in which k and Fº are constants. The particle when disturbed will oscillate (a) about …

29. Mercury does not wet glass, wood or iron because

(a) Cohesive force is less than adhesive force (b) Cohesive force is greater than adhesive force (c) Angle of contact is less than 90o (d) Cohesive force is equal to adhesive force Ans. b (28)