(c) be heard upto 10 km from it
   (d) not be heard at any distance at all from it
Ans: (d)
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
Ans: (b)
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
Ans: (a)
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
Ans: (c)
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
Ans: (a)
249. Out of the following which is an insulator?
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