A large number of free electrons are present in metals. Why is there no current in the absence of electric field across ot, but threre is a current in the presence of electric field?
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The current is due to flow of charge in a definite direction. In a metal, the free electrons move in all directions haphazardly, in the absence of electric field , the average thermal velocity of electrons is zero. Therefore, there is no current in metal in the absence of electric field. In the presence of electric field, each free electron experiences a force opposite to the direction of experiences a force opposite to the directgon of field. Therefore, the electrons acquire a drift velocity and there is a net flow of charge in a definite direction which constitutes the current.
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