Physics Page-8

71) A car is running on a road at a uniform speed of 60 km/hr. The net resultant force on the car is
(A) Driving force in the direction of car's motion
(B) Resistance force opposite to the direction of car's motion
(C) An inclined force
(D) Equal to zero

72) Which one of the following is not an advantage of AC over DC?
(A) The AC sows skin effect
(B) In AC a wide range of voltages is possible
(C) Lines loss In AC transmission lines are negligible
(D) In AC the magnitude of current can be reduced by a choke

73) Which of the following instruments may be used to measure A.C?
(A) Galvanometer
(B) Hot-wire ammeter
(C) Moving coil galvanometer
(D) None of these

74) Copper wires are generally used for electrical power transmission instead of iron wires because
(A) Copper is a better conductor than iron
(B) Copper is cheaper than iron
(C) Copper can take higher power than iron
(D) Copper is lighter than iron

75) Permanent magnets are made from
(A) Diamagnetic substances
(B) Ferromagnetic substances
(C) Paramagnetic substances
(D) Dielectric substances

76) Which one of the following is not an advantage of three phase system of electric power supply over one phase system?
(A) The output voltage is higher
(B) The power consumption is less
(C) The total output is almost constant
(D) The output of a 3-phase machine is greater than that of a single phase machine

77) Ball bearings are used to reduce friction by.
(A) Applying lubricants to the balls used
(B) Reducing the area of contract with the use of metallic balls
(C) Increasing the area of contact with the use of metallic balls
(D) None of these

78) An electric motor runs on which principle?
(A) Electrical energy can be convened into chemical energy in the presence of magnetic fields
(B) A conductor carrying current in the direction perpendicular to the external magnetic field feels a force
(C) The current flowing through a conductor causes generation of heat that drives the engine
(D) Changing magnetic field induces an electromotive force in a conductor

79) Which of the following functions is performed by a photocell?
(A) It converts chemical energy into electrical energy
(B) It converts magnetic energy into electrical energy
(C) It converts light energy into electrical energy
(D) It converts electrical energy into light energy

80) Electronics is the study of
(A) Flow of molecules
(B) Flow of electrons
(C) Flow of photons
(D) All are true



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