219. Hydrophone is an instrument used
(a) for measuring relative density of liquids
(b) by ships to pass on messages
(c) for determining the depth of ocean bottoms etc.
(d) by deaf people to aid hearing
220. Bats flying in the dark avoid obstacles because
(a) they can see very dearly only in darkness
(b) they produce ultrasonic waves which guide them
(c) their eyes are sensitive to darkness
(d) their eye holes expand in darkness
221. When two similar sources vibrate with slightly different frequencies, a regular rise and fall occurs in the loudness of tone. This phenomenon Is known as
(a) doppler effect
(b) beats
(c) resonance
(d) echo
222. When sound waves travel from one medium to another, the quantity which remains unchanged is its
(a) speed
(b) frequency
(c) wavelength
(d) All the above
223. In a concert hall reverberation is controlled by
(a) reduction of seating capacity in the hall
(b) increase of sound intensity in the hall
(c) lining the walls, with leather panels put on over a layer of sound absorbent glass fibre
(d) by opening the doors and windows of concert hall
224. When a whistling engine approaches a person standing on the platform, the frequency or the note
(a) appears to increase
(b) appears to decrease
(c) does not change at all
(d) first increases then decreases
225. Sound waves In ‘air travel faster if
(a) frequency is higher
(b) wavelength is smaller
(c) pitch is smaller
(d) air is warmer
226. The acoustical quality of a room depends on
(a) the size and shape of the room
(b) the ability of the ceiling, walls and floor to exclude unwanted sound
(c) the use of furnishings made of sound absorbing materials
(d) All the above
227. Ultrasonic waves are used –
(a) in medical and surgical diagnosis
(b) in testing the quality of the linings and pads used in vehicles and aircraft brakes
(c) to clean surgical instruments, jewellery and similar articles
(d) All the above
228. SONAR (Sound Navigation Ranging) is
(a) used by warships and military aircraft to locate enemy submarines
(b) used by ships to determine the depth of water beneath them
(c) a detective device that uses sound to locate under – water objects
(d) All the above
229. A device used in a ship for the purpose of measuring the depth of the sea is
(a) an altimeter
(b) a fathometer
(c) a hydrometer
(d) a sonometer
230. The scientist who first sent electromagnetic waves to distant places was
(a) James Clerk Maxwell
(b) Heinrich Hertz
(c) Thomas Alva Edison
(d) Baird
231. Like magnetic poles
(a) attract each other
(b) repel each other
(c) neither attract nor repel
(d) attract or repel depending upon the conditions
232. The strength of an electromagnet can be increased by
(a) increasing the length of the coiled wire
(b) increasing current supply
(c) increasing the size of the iron core
(d) All the above
233. Among the following the most suitable material for the core of an electro- magnet is
(a) steel
(b) wood
(c) soft iron
(d) copper