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Physical Science

221)A clearly sepate echo of a sound is heard when the minimum distance of the reflecting surface from the source of sound is
17m 19m
16m 18m
Answer :

222)The walls and ceiling of an auditorium are covered with fibrous materials, such as glass fibre, to
beautify the auditorium make the auditorium fire proof
reduce the cost of construction absorb sound and prevent echoes
Answer :

223)Bats can fly in the dark because
the pupils of their eyes are very big they have better vision at night
they are guided by ultrasonic waves produced by them any bird can do that
Answer :

224)A police van sounding its siren is moving away from an observer. The pitch of the sound from the siren relative to its normal pitch is
higher no change
lower lower or higher on the speen of the van
Answer :

225)If a bar magnet, tied in the middle with a thread, were suspended at the north pole of the earth, it would take
horizontal position nearly vertical position with its north pole pointing downward
nearly vertical position with its south pole pointing downward a slanting position
Answer :

226)Two pins sticking vertically at the end of a bar magnet do not hang vertically because
similar poles repel their heads are not properly rounded
of the spherical shape of their heads they are made of a magnetic material
Answer :

227)The crackling sound, heard when dry hair is combed with a hard rubber comb, is due to
small electric sparks the rubbing of the comb with the hair
the hair banging against the charges comb None of these
Answer :


228)A capacitor is used in an electrical circuit to
step up viltage store charge
step down voltage produce electric charge
Answer :

229)Which of the following is a semiconductor ?
wood glass
phosphorus silicon
Answer :

230)"IC Chips" for electronic devices are usually made of
silicon chromium
coal lead
Answer :

231)Which of the following would be most suitable for making an electromagnet?
steel soft iron
copper chromium
Answer :

232)Which of the following does not rely on the magnetic effect of current for its working ?
telephone receiver fan
dynamo carbon microphone
Answer :

233)Nichrome wire is used as a heating element in many appliances because
it has high resistivity it resists oxidation in air when red hot
it can be drawn out into wires easily both (a) and (b)
Answer :

234)Which of the following devices converts electrical energy into mechanical energy ?
electric motor dynamo
transformer inductor
Answer :

235)Which of the following devices converts mechanical energy into electrical energy ?
electric motor dynamo
transformer inductor
Answer :

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