The thermal speeds of free electrons are very large. In spite of these high speeds, why they fails to escape from the surface of a conductor?

      The thermal speeds of free electrons are very large. In spite of these high speeds, why they fails to escape from the surface of a conductor?

     

      Free electrons in a conductor are free only to the extent that they may move from one atom to another in the conductor. This is because the free electrons starting at the surface of conductive found behind the positive ions attract them back and pulling forward. So on the surface of a superconductor, free electron encounters forces that keep him out of the conductor surface. External energy is required to free electrons escape the conductor surface.