A radar which detects the presence of an enemy aircraft uses _____.

1. 1. Radio-waves 
   2. Electric waves
   3. Sound waves
   4. Ultrasonic waves

In the process of galvanization an iron sheet is coated with _____.

1. 1. Tin
   2. Galena
   3. Tin
   4. Radio-waves 

What are ultrasonic waves?

1. 1. Sound waves produced in a vacuum
   2. Sound waves having frequency higher than audio-frequency range
   3. Sound waves having frequency shorter than audio-frequency range
   4. None of these

The process of transfer of heat by matter but without actual movement of the particles themselves is called _____.

1. 1. Radiation
   2. Convection
   3. Conduction
   4. All of these

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 _____.

1. 1. Diffusion
   2. Sublimation
   3. Evaporation
   4. Vaporisation

In deserts coulds do not precipitate because of _____.

1. 1. High wind velocity
   2. Low temperature
   3. Low pressure
   4. Low humidity

If we go to the Himalayas, we feel breathless because _____.

1. 1. It is very cold there
   2. The density of air is high on the hills reducing oxygen content
   3. the density of air is much less on the hills so oxygen content is reduced
   4. All of these

Cloudy nights are warmer because _____.

1. 1. Clouds prevent radiation of heat form ground to air
   2. Of the compact density of air
   3. More dust particles gather in the air
   4. Of low atmospheric pressure

In diesel engines ignition takes place by _____.

1. 1. Dynamo
   2. Electrical spark
   3. Battery
   4. Compression

Water cannot be used to extinguish fire caused by an electric current because _____.

1. 1. It may cause hydrolysis
   2. It may cause another short circuit
   3. It may cause electrocution
   4. It will spoil the wiring