physics : class12 Conduction Band : Insulators : Electronic Devices MCQ Questions and Answers
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Conduction Band
MCQ questions and answers.
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MCQ Questions
1. What is the conduction band in an insulator?
A.
The band containing tightly bound core electrons
B.
The band of energy levels in which electrons can move freely to conduct electricity
C.
The band containing only protons
D.
The band with no possible energy levels
Correct Answer:
The band of energy levels in which electrons can move freely to conduct electricity
Explanation:
The conduction band consists of energy states in which electrons are sufficiently free to move through the material and contribute to electrical conduction.
2. At ordinary temperatures, the conduction band of an ideal insulator is generally:
A.
Completely filled with electrons
B.
Partly filled with electrons
C.
Nearly empty of electrons
D.
Filled only with positive charges
Correct Answer:
Nearly empty of electrons
Explanation:
In an insulator, electrons normally cannot gain enough energy to reach the conduction band, so it remains nearly empty at ordinary temperatures.
3. Why does an insulator have very few electrons in its conduction band at room temperature?
A.
Its conduction band is separated by a large energy gap
B.
Its conduction band contains no energy states
C.
Its conduction band is below the nucleus
D.
Its conduction band is filled with neutrons
Correct Answer:
Its conduction band is separated by a large energy gap
Explanation:
A large forbidden energy gap makes it difficult for electrons to gain enough energy to enter the conduction band.
4. An electron in the conduction band of an insulator can contribute to current because it:
A.
Is free to move through the material
B.
Has become a proton
C.
Remains fixed at its atomic position
D.
Has no electric charge
Correct Answer:
Is free to move through the material
Explanation:
Electrons occupying conduction-band states are mobile and can move under an applied electric field, producing electric current.
5. In an insulator, the conduction band is usually located:
A.
Below the valence band
B.
Above the valence band with a large energy gap
C.
Inside the atomic nucleus
D.
At exactly the same energy as the valence band
Correct Answer:
Above the valence band with a large energy gap
Explanation:
The conduction band lies above the valence band, and the large separation between them prevents easy electron excitation in an insulator.
6. What happens when an electron in an insulator gains enough energy to cross the forbidden gap?
A.
It enters the conduction band
B.
It disappears from the material
C.
It changes into a neutron
D.
It enters the nucleus
Correct Answer:
It enters the conduction band
Explanation:
An electron that receives energy equal to or greater than the band gap can move into the conduction band and become available for conduction.
7. The electrical conductivity of an insulator is low mainly because its conduction band is:
A.
Highly populated with mobile electrons
B.
Nearly empty under normal conditions
C.
Filled with holes only
D.
Connected directly to the nucleus
Correct Answer:
Nearly empty under normal conditions
Explanation:
Very few electrons occupy the conduction band in an insulator, so there are very few mobile charge carriers to conduct electricity.
8. Which type of electron is most directly responsible for conduction when it occupies the conduction band?
A.
A mobile electron
B.
A neutron
C.
A proton fixed in the nucleus
D.
An electron permanently fixed to an atom
Correct Answer:
A mobile electron
Explanation:
An electron in the conduction band is mobile and can respond to an electric field, thereby contributing to electrical conduction.
9. Compared with a conductor, an insulator has a conduction band that is:
A.
More easily populated with electrons
B.
Separated from available electrons by a larger energy gap
C.
Always completely filled
D.
Absent from the material
Correct Answer:
Separated from available electrons by a larger energy gap
Explanation:
The large energy gap in an insulator makes it difficult for electrons to reach the conduction band, unlike in a conductor.
10. If the conduction band of an insulator remains empty, the material will have:
A.
Many freely moving electrons
B.
Very little electrical conduction
C.
Maximum electrical conduction
D.
Only positive current from protons
Correct Answer:
Very little electrical conduction
Explanation:
An empty or nearly empty conduction band provides very few mobile electrons, so the insulator conducts very little electricity.
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