Question

a- Consider an electron that moves freely in metal and a particle moves freely in vacuum. Briefly explain differences between the energy of these particles. b- Briefly explain the temperature dependent conductivity of metal, semiconductor and insulator. (Please write your answer by asking your self “How and Why change” questions )

Answer 1

a) The energy of an electron moving freely in a metal changes with time . Also it moves in a potential field created by the ions and other electrons present in the metal .As the electron collides with other ions and electrons the energy of the electron changes over time.

Where energy of  a particle moving in vaccum is constant over time ,as there is no ion or other particles to collide.

so energy remains constant.

b)For Metal : as the temperature rises in a metal the conduction free electron experiences more collision with the ions and other electrons in the metal . So resistance of the metal increases . As a result conductivity decreases.

For semiconductor: Conductivity in a semiconductor depends on the number of electron produced by breaking of covalent bonds of the semiconducting material. With the rise in temperature the no of covalent bond breaking increases . So no of electron increases with rise in temperature. As a result conductivity increases.

For insulator: for insulator the band gap between valence electorn and conducting electron is so high that there is no free electron in an insulator. If we increase temperature , due to high band gap no electron can jump from valence band to conduction band . So there in no free electron after increasing temperature.

so conductivity of an insulator does not change with temperature and its conductivity is almost zero.

Thank You.