Question:
In which of the following materials the resistance decreases with increase in temperature ?
In which of the following materials the resistance decreases with increase in temperature ?
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- Conductors (metals like Cu, Pt, Hg) \(\rightarrow\) Resistance increases as temperature increases.
- Semiconductors and insulators (Carbon, Silicon, Germanium) \(\rightarrow\) Resistance decreases as temperature increases.
- Semiconductors and insulators (Carbon, Silicon, Germanium) \(\rightarrow\) Resistance decreases as temperature increases.
Updated On: Jul 21, 2026
- Copper
- Carbon
- Mercury
- Platinum
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
The electrical resistance of a material changes with temperature.
How a material behaves depends on whether it has a Positive Temperature Coefficient (PTC) or a Negative Temperature Coefficient (NTC) of resistance.
Detailed Explanation:
Let us analyze how the different materials behave:
- Metals (Copper, Mercury, Platinum):
Metals contain a high concentration of free conduction electrons.
When the temperature of a metal increases, the positive metal ions in the crystal lattice vibrate more intensely.
These thermal vibrations scatter the moving electrons, making it more difficult for them to flow.
Therefore, metals have a Positive Temperature Coefficient, meaning their resistance increases with temperature.
- Semiconductors and Metalloids (Carbon):
At low temperatures, carbon (in graphite or amorphous form) has relatively few electrons in its conduction band.
As temperature increases, thermal energy excites more valence electrons across the small band gap into the conduction band, significantly increasing the concentration of charge carriers.
This increase in conduction electrons outweighs any resistance from lattice vibrations, causing the electrical resistance of carbon to decrease with temperature.
Thus, Carbon has a Negative Temperature Coefficient of resistance.
Step 2: Final Answer:
The resistance of Carbon decreases as temperature increases.
The electrical resistance of a material changes with temperature.
How a material behaves depends on whether it has a Positive Temperature Coefficient (PTC) or a Negative Temperature Coefficient (NTC) of resistance.
Detailed Explanation:
Let us analyze how the different materials behave:
- Metals (Copper, Mercury, Platinum):
Metals contain a high concentration of free conduction electrons.
When the temperature of a metal increases, the positive metal ions in the crystal lattice vibrate more intensely.
These thermal vibrations scatter the moving electrons, making it more difficult for them to flow.
Therefore, metals have a Positive Temperature Coefficient, meaning their resistance increases with temperature.
- Semiconductors and Metalloids (Carbon):
At low temperatures, carbon (in graphite or amorphous form) has relatively few electrons in its conduction band.
As temperature increases, thermal energy excites more valence electrons across the small band gap into the conduction band, significantly increasing the concentration of charge carriers.
This increase in conduction electrons outweighs any resistance from lattice vibrations, causing the electrical resistance of carbon to decrease with temperature.
Thus, Carbon has a Negative Temperature Coefficient of resistance.
Step 2: Final Answer:
The resistance of Carbon decreases as temperature increases.
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