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| 72)Which one of the following is the best conductor of heat? | |||
| water | mercury | ||
| ether | alcohol | ||
| Answer : | |||
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| 73)An iron hammer lying in the sun appears much hotter than its wooden handle because | |||
| iron is at higher temperature | iron is darker than wood | ||
| iron absorbs more heat | iron is a good conductor of heat | ||
| Answer : | |||
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| 74)A thermostat is a device used | |||
| to switching off an electrical appliance | measuring temperature | ||
| regulating temperature | producing heat | ||
| Answer : | |||
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| 75) A Pyrex pot does not crack when hot water is poured on it because | |||
| it is a strong meterial | does not expand much on heating | ||
| is good conductor of heat | expands equally from inside and outside | ||
| Answer : | |||
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| 76)Woollen cloths keep us warm in winter because | |||
| it produces more heat | it is good conductor of heat | ||
| it do not allow heat from our body to escape | it do not allow cool air to enter | ||
| Answer : | |||
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| 77)By what process is heat transmitted from the filament of a bulb to the glass? | |||
| conduction | convection | ||
| radiation | none of these | ||
| Answer : | |||
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| 78)Hot coffee is poured simultaneously in four metallic cups painted outside with different types of paints. After some time, the coffee will be found coldest in the cup painted | |||
| rough white | shining white | ||
| rough black | shining black | ||
| Answer : | |||
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| 79)Light colour dresses are preferred in summer because | |||
| light colour is good radiator of heat | light colour is poor absorber of heat | ||
| it soaks sweat faster | they allow body heat to escape faster | ||
| Answer : | |||
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| 80)By which of the methods a cup of hot coffee lose heat if placed on a metal table in a room? | |||
| conduction and radiation | conduction and convection | ||
| convection and radiation | conduction, convection, radiation and evaporation | ||
| Answer : | |||
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| 81)A cup of tea cools from 90 degree Celsius to 80 degree Celsius in exactly one minute. It will cool from 70 Celsius to 60 degree Celsius in | |||
| less than one minute | exactly one minute | ||
| nearly in one minute | more than one minute | ||
| Answer : | |||
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| 82)Drinks remain hot or cold for a long time in a thermos flask because of the | |||
| presence of air, which is a bad conductor of heat, in between the double walls | silver coating on the inside of the double walls | ||
| vacuum between the double walls | combine effects of (b) and (c) | ||
| Answer : | |||
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| 83)For a given liquid, the rate of evaporation depends on | |||
| the temperature of the liquid | the temperature of air | ||
| the surface area of the container | all of these | ||
| Answer : | |||
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| 84)A little ether on the palm gives a cooling sensation because | |||
| it is a cold liquid | absorbs heat from palm and evaporates | ||
| enters the pores of the skin | condenses on the palm | ||
| Answer : | |||
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| 85)Water stored in earthen jar remain cool because | |||
| earthen jar has high heat capacity | earthen jar radiate heat quickly | ||
| water oozing out of the pores of the jar get evaporated | earthen jar absorbs heat from water | ||
| Answer : | |||
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| 86)We feel comfortable under a fan during summer because | |||
| it throws cool air on us | it sets the air in motion and increases the evaporation rate of sweat | ||
| it produces convection current | it produces air which takes heat away | ||
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