Physics
In a conductor

The forbidden energy gap is very wide
The forbidden energy gap is very narrow
The valence band and the conduction band overlap each other
There is no conduction band

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Physics
Railway tracks are banked on curves

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

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