234. If a bar magnet is broken into two pieces
(a) both pieces will lose their magnetism
(b) one piece will have North Pole on both ends and the other South Pole on its both ends
(c) each will remain a magnet with North Pole at one end and South Pole at the other
(d) the longer piece will behave as a bar magnet while the smaller will have no magnetism at all
235. A permanent magnet may be demagnetised by
(a) placing it inside a solenoid through which an alternating current is flowing
(b) heating the magnet to redness and then allowing it to cool
(c) dropping it several times or hammering it while lying east-west
(d) All the above
236. A sensitive instrument susceptible to magnetic infiuence can be protected from external magnetic field by
(a) enclosing it in a thick walled iron box
(b) wrapping it with an insulator
(c) by placing it inside a glass case
(d) by surrounding it with fine copper gauze
237. A bar magnet tied in the middle with a thread is suspended at the South
Pole of the earth. The magnet will be in
(a) a horizontal position
(b) a nearly vertical position with its South Pole downwards
(c) a nearly vertical position with its North Pole downwards
(d) a slanting position
238. The line on earth’s surface passing through the places having zero dip is called the magnetic equator. This passes through
(a) Thumba
(b) Delhi
(c) Mumbai
(d) Sriharikota
239. Electromagnets are used in
(a) the telephone ear piece
(b) the telegraph
(c) the electric bell
(d) All the above
240. The Cact that the compass needle does not point true north was observed first by
(a) Sir Isaac Newton
(b) Columbus
(c) Archimedes
(d) Thomas Alva Edison
241. The loudness of a sound is determined by
(a) Frequency
(b) Amplitude
(c) Speed
(d) Wavelength
242. A person cups his hand around the mouth when shouting. Why?
(a) Sound energy from his mouth is then directed in one direction
(b) The cupped hand acts as a cardboard tube of short length
(c) The pitch of sound increases
(d) Both (a) and (b)
243. If a man wants to hear clearly the echo of a sound produced by him from a hill, the hill should be away from him by a minimum distance of
(a) 330 m
(b) 33 m
(c) 16.5 m
(d) 165 m
244. If a band is played on the moon the sound will
(a) reverberate
(b) be heard by us faintly
(c) be heard upto 10 km from it
(d) not be heard at any distance at all from it
245. If you want a sound proof room, the walls should be
(a) able to refract the sound
(b) good absorbers of sound
(c) good reflectors of sound
(d) All the above
246. When a charged rod is brought near a collection of small pith balls, the balls
(a) will jump rapidly up and down for a short time
(b) will remain unaffected
(c) Both (a) and (b) above
(d) It will produce electric shock
247. In experiments on static electricity the standard method for obtaining small amounts of positive electricity is to rub
(a) a glass rod with flannel
(b) an abonite rod with flannel
(c) a glass rod with silk
(d) Any of the above
248. The force of attraction or repulsion between two charged bodies is directly proportional to the product of the charges and inversely proportional to the square of distance between them. This was propounded by
(a) Coulomb
(b) Gilbert
(c) Volta
(d) Rutherford
249. Out of the following which is an insulator?
(a) Silver
(b) Copper
(c) Nichrome
(d) Dry wood
250. A rod of brass is held in hand and rubbed with fur. The rod is found to have
(a) no charge
(b) positive charge
(c) negative charge
(d) can’t be said