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Physical Science |
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| 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 | ||
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| 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 : | |||
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| 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 | ||
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| 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 | ||
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| 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 | ||
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| 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 : | |||
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| 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 | ||
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| 228)A capacitor is used in an electrical circuit to | |||
| step up viltage | store charge | ||
| step down voltage | produce electric charge | ||
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| 229)Which of the following is a semiconductor ? | |||
| wood | glass | ||
| phosphorus | silicon | ||
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| 230)"IC Chips" for electronic devices are usually made of | |||
| silicon | chromium | ||
| coal | lead | ||
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| 231)Which of the following would be most suitable for making an electromagnet? | |||
| steel | soft iron | ||
| copper | chromium | ||
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| 232)Which of the following does not rely on the magnetic effect of current for its working ? | |||
| telephone receiver | fan | ||
| dynamo | carbon microphone | ||
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| 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) | ||
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| 234)Which of the following devices converts electrical energy into mechanical energy ? | |||
| electric motor | dynamo | ||
| transformer | inductor | ||
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| 235)Which of the following devices converts mechanical energy into electrical energy ? | |||
| electric motor | dynamo | ||
| transformer | inductor | ||
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