## Physics Questions and Answers – Part7

61. What enables us to write on the black board with chalk?
a. Gravity
b. Cohesion
d. Viscosity

62. You placed a car in an open a parking area in a summer day. After a few hours, you noticed that the heat is trapped inside the car. This phenomenon is known as
a. Ozone depletion
b. Greenhouse effect
c. Solar effect
d. Cosmic ray impingement
b. Greenhouse effect

63. Hair of a shaving brush cling together when the brush is removed from water due to
a. Viscosity
b. Elasticity
c. Friction
d. Surface tension
d. Surface tension

64. SONAR is mostly used by
a. Doctor
b. Engineers
c. Astronauts
d. Navigators
d. Navigators

65. Ball bearings are used in bicycles, cars, etc., because
a. The actual area of contract between the wheel and axle is increased
b. The effective area of contract between the wheel and axle increased
c. The effective area of contact between thee wheel and axle is reduced
d. None of the above statements is correct
c. The effective area of contact between thee wheel and axle is reduced.

66. On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because
a. mercury is a metal
b. density of mercury is greater than that of water
c. cohesion of mercury is greater than its adhesion with glass
d. cohesion of water is greater than its adhesion with glass
c. cohesion of mercury is greater than its adhesion with glass

67. Suitable impurities are added to a semiconductor depending on its use. This is done in order to
a. increase its life
b. enable it to withstand higher voltages
c. increase its electrical conductivity
d. increase its electrical resistivity
c. increase its electrical conductivity

68. Stars twinkle because
a. the intensity of light emitted by them changes with time
b. the distance of the stars from the earth changes with time
c. the refractive index of the different layers of the earth’s atmosphere changes continuously, consequently the position of the image of a start changes with time
d. the light from the star is scattered by the dust particles and air molecules in the earth’s atmosphere
c. the refractive index of the different layers of the earth’s atmosphere changes continuously, consequently the position of the image of a start changes with time

69. It takes much longer to cook food in the hills than in the plains, because
a.  in the hills the atmospheric pressure is lower than that in the plains and therefore water boils at a temperature lower than 100oC causing an increase in cooking time
b.  due to low atmospheric pressure on the hills, the water boils at a temperature higher than 100oC and therefore water takes longer to boil
c.  in the hills the atmospheric density is low and therefore a lot of heat is lost to the atmosphere
d.  in the hills the humidity is high and therefore a lot of heat is absorbed by the atmosphere leaving very little heat for cooking
a.  in the hills the atmospheric pressure is lower than that in the plains and therefore water boils at a temperature lower than 100oC causing an increase in cooking time

70. Moment of inertia is
a. vector
b. scalar
c. phasor
d. tensor
d. tensor