Gen. Science

72)Which one of the following is the best conductor of heat?
water mercury
ether alcohol
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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
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74)A thermostat is a device used
to switching off an electrical appliance measuring temperature
regulating temperature producing heat
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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 :

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
Answer :

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