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Exercise

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31 

On a cold day when a room temperature is 15oC, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of 15oC, because

A. metals have higher thermal capacity than plastics
B. plastics have a lower density than metals
C metals are good conductor of heat
D. plastics have a higher thermal conductivity than metals

32 

Railway tracks are banked on curves

A. necessary centrifugal force may be obtained from the horizontal component weight of the train
B. to avoid frictional force between the tracks and wheels
C necessary centripetal force may be obtained from the horizontal component of the weight of the train
D. the train may not fly off in the opposite direction

33 

Light travels at the fastest speed in

A. glass B. water
C. hydrogen D. vacuum

34 

Superconductors are substances which

A. conduct electricity at low temperature
B. offer high resistance to the flow of current
C offer no resistance to the flow of electricity
D. conduct electricity at high temperatures

35 

oil raise up the wick in a lamp. The principle involves

A. the diffusion of oil through the wick
B. the liquid state of oil
C capillary action phenomenon
D. volatility of oil

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