Ans: (c)
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
Ans: (d)
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
Ans: (a)
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
Ans: (c)
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
Ans: (a)
239. Electromagnets are used in
   (a) the telephone ear piece
   (b) the telegraph
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