Physics

(i) What are free electrons?

(ii) Why do they not leave the metal surface on their own?

(iii) How can they be made to leave the metal surface? (State any two ways)

Radioactivity

ICSE 2017

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Answer

(i) The loosely bound outer most electrons of atoms in a metal which leave their atoms and become free to move inside the metal are called the free electrons.

(ii) The free electrons can move in a random manner inside the metal but they do not have sufficient kinetic energy to leave the metal surface.

(iii) The free electrons can be made to leave the metal surface by imparting energy from outside either :

  1. by heating in thermionic emission.
  2. by making the ultraviolet radiation incident on it in photoelectric effect.

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