It is known that the drift velocity of electrons is only a few mm/s for a current of a few amperes. How is it possible that a current is established almost instantaneously when a circuit is closed?

For example, a bulb glows as soon as the connection is switched on

The current is established almost instantaneously because an electric field is set up in the electric circuit as soon as it is closed, almost with the speed of light.

  • This leads to drift of local electron at each point in the circuit.
  • The establishment of a current does not require individual electrons to move from one end to the other end of the conductor.
  • Each free electron in the conductor accelerates due to the effect of the electric field until it collides with a positive metal ion and loses its drift velocity.
  • The electrons go through a continuous collision cycle and successive loosing of drift speed until an average drift speed is obtained.

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                          CBSE CLASS XII Previous Year Papers

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