Ans : (b)
176. The most efficient engine is : [NDA 1990]
       (a) petrol
       (b) diesel
       (c) electric
       (d) steam
Ans : (c)
177. Consider the following statements about a thermos flask: [NDA 1993]
     1) It is a practical device in which the heat flowing into or out of the system by conduction, convection or radiation is reduced as
          much as possible.
     2) It consists of a double-walled glass vessel.
     3) The heat transfer by convection is minimized by silvering the surfaces and the radiation is minimized by evacuating the space
          between the walls.
     Of these, the correct ones are:
     (a)  1 and 2
     (b)  2 and 3
     (c)  1 and 3
     (d)  1, 2 and 3
Ans : (a)
178. An electric motor runs on which principle?
     (a) Electrical energy can be converted 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
Ans : (b)
179. Ball bearinqs are used to reduce friction by:
     (a) applying lubricants to the balls used
     (b) reducing the area of contact with the use of metallic balls
     (c) increasing the area of contact with the use of metallic balls
     (d) None of the above
Ans : (b)
180. What is the function of a microprocessor in a computer? [RRB 1994]
     (a) It allows the key board to write on the computer
     (b) It allows the outputs to be taken from a computer
     (c) It performs all the functions of a CPU (Central Processing Unit)
     (d) None of the above
Ans : (c)
181. Given: Humidity - H High -A,
     Wind velocity - W Low - B
     Temperature - T
     The desert cooler is an appropriate cooling device for regions where
     (a) H-A, W-A, T-A
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