Question

On heating, the resistance of a semiconductor
1. increases
2. decreases
3. remains same
4. first increases and then decreases
5. None of the above / More than one of the above

Answer 1

Correct Answer - Option 2 : decreases

The correct answer is Decreases.

• On heating, bonds between the electrons of semiconductor break because of the energy gained due to heating.
  • Electrons become free & help in conduction of electric current if there is a potential difference is applied across the semiconductor.
  • Hence the resistance decreases on heating.

• Resistance:
  • ​It is the ability of the material to oppose the flow of current through the conductor.
  • It depends on the following factors:
    • Length.
    • Area.
    • Temperature.
    • Type of material.
  • R = p L / A.
    • Where p = resistivity of the material.
    • L = length of the conductor.
    • A = cross-sectional area of the conductor.
  • SI Unit = Ohm.
  • In the case of a conductor, resistance increases on heating.
• Resistivity:
  • It is the electrical property of a material that determines the resistance of a conductor.
  • It depends upon the nature & temperature of the material.
  • SI unit: Ohm- metre.
• Semiconductor:
  • ​It is the type of material having conductance lesser than conductor & resistance lesser than insulators.
  • They do not have free electrons at normal temperature.
    • On heating, the electrons get free & they behave like a conductor.
  • The entire electronic system is based on semiconductor devices.
  • Materials like Si, Ge, As etc are the semiconductors.
  • A pure semiconductor is neither n-type nor p-type.
    • Both p-type & n-type semiconductor is electrically neutral.
  • It is of two types:
    • Intrinsic:
      • It is a semiconductor in pure form.
      • E.g: Germanium (Ge), Silicon (Si) etc.
    • Extrinsic:
      • It is a semiconductor mixed with a suitable impurity to increase its conductivity.
      • It is further classified into two groups:
        • n-type: It is mixed with pentavalent impurity like As, Sb etc. in which negatively charged electrons work as charge carriers.
        • p-type: It is mixed with trivalent impurity like Al, B etc. in which positively charged holes works as charge carriers.

• Electric current:​
  • ​It is the rate of flow of charge.
  • Its magnitude is equal to the rate of flow of electric charge through a conductor.
  • Electric current: I = ne/t.
    • Where n = number of electrons flowing through a conductor.
    • e = electric charge i.e
      • e = 1.6 x 10-19C.
    • t = time period.
  • It is a scalar unit.
  • SI unit: Ampere (A).