121) Water cannot be used to extinguish the fire caused by an electric current because
(A) It may cause another short circuit
(B) It may cause hydrolysis
(C) It may cause electrocution
(D) It will spoil the wiring
122) In diesel engines, ignition takes place by
(A) Compression
(B) Electrical spark
(C) Dynamo
(D) Battery
123) Cloudy nights are warmer because
(A) Clouds prevent radiation of heat from ground to air
(B) Of low atmospheric pressure
(C) Of the compact density of air
(D) More dust particles gather in the air
124) If we go to the Himalayas, we feel breathless because
(A) It is very cold there
(B) The density of air is much less on the hills so oxygen content is reduced
(C) The density of air is high on the hills reducing oxygen content
(D) None
125) In deserts, clouds do not precipitate because of
(A) Low pressure
(B) Low humidity
(C) High wind velocity
(D) Low temperature
126) When an open bottle of scent is kept in a corner of the room, its odor is felt in all the corners. This is due to the phenomenon of
(A) Vaporisation
(B) Evaporation
(C) Diffusion
(D) Sublimation
127) The process of transfer of heat by matter but without actual movement of the particles themselves is called
(A) Conduction
(B) Convection
(C) Radiation
(D) None of the above
128) What are ultrasonic waves?
(A) Sound waves having frequency shorter than audio-frequency range
(B) Sound waves produced in a vacuum
(C) Sound waves having frequency higher than audio-frequency range
(D) None of these
129) In the process of galvanization an iron sheet is coated with
(A) Aluminium
(B) Zinc
(C) Tin
(D) Galena
130) A radar which detects the presence of an enemy aircraft uses
(A) Sound waves
(B) Radiowaves
(C) Electric waves
(D) Ultrasonic waves