(a) high conductivity and low temperature
coefficient
(b) high conductivity and large temperature coefficient
(c) low conductivity and zero temperature coefficient
(d) low conductivity and high temperature coefficient
Correct Answer: (b)
Explanation
Pure metals conduct well and show significant
resistance change with temperature.
Notes for
More Information
Temperature Effect on
Conductivity and Resistivity
In Metals
1. Pure metals have very
high electrical conductivity.
2. This is
because metals contain a large number of free electrons.
3. When temperature
increases:
·
The number of free electrons remains almost constant.
·
But the mobility of electrons decreases.
4. The
decrease in mobility is due to increased lattice vibrations of
metal atoms.
5. These
vibrations cause more collisions (lattice scattering) between
electrons and atoms.
6. As a
result, resistivity increases.
7. Hence,
metals have a positive temperature coefficient of resistivity.
In Semiconductors
8. In semiconductors,
the behavior is different.
9. When temperature
increases:
·
More electrons gain energy.
·
Electrons are excited from the valence band to the conduction
band.
10.
This leads to a large increase in carrier concentration.
11.
Due to more charge carriers:
·
Conductivity increases
·
Resistivity decreases
12.
Therefore, semiconductors have a negative temperature
coefficient of resistivity.
13.
In intrinsic semiconductors, the dominant factor is
the increase in the number of free electrons.
14.
Hence, the specific resistance of semiconductors decreases with
increasing temperature.
Key Difference Between Metals
and Semiconductors
15.
The difference in temperature behavior arises mainly due to:
·
Metals → carrier concentration
remains constant; mobility decreases.
·
Semiconductors → carrier concentration
increases rapidly with temperature.
16.
Thus, the variation of resistance with temperature is
fundamentally different for metals and semiconductors.
Important Conclusion
(MCQ-Oriented)
17.
Pure metals generally have:
·
High electrical conductivity
·
Large temperature coefficient of resistance
18.
This means:
·
They conduct electricity very well.
·
Their resistance increases significantly with
temperature.
19.
Hence, the correct option is (b): high conductivity and large
temperature coefficient.
Contrast with Alloys
20.
Alloys (such as manganin and
constantan):
·
Have lower conductivity than pure metals.
·
Possess very small or nearly zero temperature coefficient.
21.
Because of this, alloys are preferred for:
·
Precision resistors
·
Stable resistance applications, where
temperature variation must have minimal effect.
Final Takeaway
22.
Metals → High conductivity, positive
and large temperature coefficient.
23.
Semiconductors → Conductivity increases
with temperature, negative temperature coefficient.
24.
Alloys → Lower conductivity
but excellent resistance stability with temperature
