Ans: (c)
235. A permanent magnet may be demagnetised by
   (a) placing it inside a solenoid through which an alternating current is
   (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