Question

By increasing the temperature, the specific resistance of a conductor and a semiconductor
A). Increases for both
B). Decreases for both
C). Increases, Decreases
D). Decreases, Increases

Answer 1

Specific resistance is expressed as the reciprocal of specific conductance, which is defined as a measure of a material's ability to conduct electricity. It means specific resistance describes the ability of a material to oppose the flow of electric current through itself. Temperature plays an important role in varying the resistivity, or specific resistance, of a material.

Complete step by step answer:
Specific resistance is defined as the value of resistance offered by a unit length and unit cross-section of a material to electric current when a voltage is applied across its terminals. It is a measure of how strongly a material opposes the flow of electric current passing through it.
For conductors:
When the temperature increases, the vibrations of the metal ions in the lattice structure increases. The atoms start to vibrate with a higher amplitude. These vibrations, in turn, cause frequent collisions between the free or valence electrons and the other electrons. Each collision drains out some energy of the free electrons and causes them unable to move. Thus, it restricts the movement of the delocalized electrons. When the collision takes place, the drift velocity of the electrons decreases. This means that the resistivity of the metal, or a conductor, increases, and therefore, current flow in the metal is decreased. The increase in resistivity results in a decrease in the conductivity of the material.
For metals or conductors, it is said that they have a positive temperature coefficient. For most of the metals, the specific resistance increases linearly with an increase in temperature.

For semiconductors:
The gap between the conduction band and the valence band is small. At zero degree kelvins, the valence band is completely filled and the conduction band may be assumed as empty. But when a small amount of energy is applied, the electrons easily tend to move to the conduction band. Under normal conditions, a semiconductor acts as a poor conductor. When the temperature rises, the forbidden gap between the two valence bands and the conduction band becomes very less and the electrons jump from the valence band to the conduction band. This way, some electrons become free to move within the structure. This increases the conductivity of the material. The conductivity increases mean that the resistivity decreases. Therefore, when the temperature is increased in a semiconductor, the density of the charge carriers also increases, and the resistivity of the material decreases.
For semiconductors, it is said that they have a negative temperature coefficient. In semiconductors, the specific resistance decreases with the increase in temperature.
By increasing the temperature, the specific resistance of a conductor increases, and a semiconductor decreases.
Hence, the correct option is C.

Note: Because specific resistance depends upon the value of the temperature coefficient of the resistance, the value of temperature coefficient for conductors is positive and for semiconductors the value is negative. Therefore, by increasing the temperature, the specific resistance of a conductor increases, and that of a semiconductor decreases.