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Electrical resistance of a piece of a material sharply decreases on increasing the temperature of the piece. The material of the piece is a:

Electrical resistance of a piece of a material sharply decreases on increasing the temperature of the piece. The material of the piece is a: Correct Answer Semi-conductor

The correct answer is option 3) i.e. semiconductor.

CONCEPT:

  • Resistance is the hindrance offered to the flow of charges. In a given material the moving free electrons in it cause a current. 
    • Resistance is inversely proportional to the current flowing. 
  • Energy band gap: It is the distance between the valence band and conduction band of material.
    • Electrons in the conduction band are responsible for current.
    • The gap between the valence band and conduction band represents the minimum energy required by an electron in the valence band to jump to the conduction band.
    • The energy bandgap for a few materials are as follows

EXPLANATION:

Conductor
  • The valence band and conduction band are overlapped, and electrons are free to move to the conduction band.
  • When the temperature is increased, the electrons acquire more energy and vibrate vigorously. This causes frequent collisions between all electrons and the net effect is that very few electrons will be available to move freely.
  • Hence, the current decreases, and therefore resistance increases.
Insulator
  • The valence band is separated far away from the conduction band. Therefore, the valence electrons require more amount of energy to jump to the conduction band.
  • When the temperature is increased, there is a lag until the electrons acquire a high amount of energy sufficient enough to move to the conduction band.
  • Hence, the current will increase gradually, and therefore resistance decreases gradually. 
Semi-conductor
  • Compared to insulators, the energy band gap is very less in semi-conductors. Thus, the electrons require very little energy to jump to the conduction band.
  • When the temperature is increased, most of the electrons acquire a sufficient amount of energy faster and jumps to the conduction band.
  • Hence, the current increases sharply, and resistance decreases sharply.
Superconductor
  • A superconductor is a material that conducts current at zero resistance.
  • This is achieved by decreasing the temperature to a certain temperature called the critical temperature.
  • When the temperature is increased, it will stop exhibiting superconductor properties, and the material is no longer a superconductor.

The current increases sharply on increasing the temperature of a semiconductor, and thus its resistance decreases sharply.

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