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Assertion: If there is some gap between ...

Assertion: If there is some gap between the conduction band and the valence band, electrons in the valence band all remain bound and no free electrons are available in the conduction band. Then the material is an insulator.
Reason: Resistance of insulators is very low

A

If both assertion and reason are true and reason is the correct explanation of assertion.

B

If both assertion and reason are true not but reason is not the correct explanation of assertion.

C

If assertion is true but reason is false

D

If both assertion and reason are false.

Text Solution

Verified by Experts

The correct Answer is:
C
If there is some gap between the conduction band and the valance band electrons in the valance band all remain bound and no free electrons in conduction band then it makes the material an insulator. Resistance of insulators is very high.
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Read the following passage and then answer question (a) - (e) on the basis of your understanding of the following passage and the related studied concepts. As per Bohr atom model, in an isolated atom the energy of any of its electrons depends on the orbit in which it revolves and it is characterised by a sharp energy level. However, inside a crystalline solid atoms are close to each other and the outer orbits of electrons from neighbouring atoms would come very close or could even overlap. As a result, each electron will have a different energy level. These different energy levels with continuous energy variation form energy bands. The energy band which includes the energy levels of the valence electrons is called the valence band. All the valence electrons reside in the valence band. The energy band above the valence band is called the conduction band. Normally the conduction band is empty. If the lowest level in the conduction band happens to be lower than the highest level of the valence band, electrons from the valence band may easily move into the conduction band and the solid behaves as a conductor. If there is some gap between the conduction band and the valence band, electrons in the valence band remain confined to it and no free electrons are available in the conduction band. It makes the solid an insulator. If some of the electrons from the valence band may gain external energy to cross the gap between the conduction band and valence band, these electrons will move into the conduction band and simultaneously create vacant energy levels in the valence band. Therefore, there is a possibility of conduction due to electrons in conduction band as well as due to vacancies in the valence band. What is the difference between energy band diagram of an insulator and a semiconductor?

Read the following passage and then answer question (a) - (e) on the basis of your understanding of the following passage and the related studied concepts. As per Bohr atom model, in an isolated atom the energy of any of its electrons depends on the orbit in which it revolves and it is characterised by a sharp energy level. However, inside a crystalline solid atoms are close to each other and the outer orbits of electrons from neighbouring atoms would come very close or could even overlap. As a result, each electron will have a different energy level. These different energy levels with continuous energy variation form energy bands. The energy band which includes the energy levels of the valence electrons is called the valence band. All the valence electrons reside in the valence band. The energy band above the valence band is called the conduction band. Normally the conduction band is empty. If the lowest level in the conduction band happens to be lower than the highest level of the valence band, electrons from the valence band may easily move into the conduction band and the solid behaves as a conductor. If there is some gap between the conduction band and the valence band, electrons in the valence band remain confined to it and no free electrons are available in the conduction band. It makes the solid an insulator. If some of the electrons from the valence band may gain external energy to cross the gap between the conduction band and valence band, these electrons will move into the conduction band and simultaneously create vacant energy levels in the valence band. Therefore, there is a possibility of conduction due to electrons in conduction band as well as due to vacancies in the valence band. How are energy bands formed in a crystalline solid ?

Knowledge Check

  • The gap between the conduction band and valence band is largest in

    A
    Semiconductors
    B
    Insulators
    C
    Conductors
    D
    None of the above

  • There is a small energy gap between the conduction and valence bands of

    A
    copper
    B
    silver
    C
    silicon
    D
    aluminium

  • There is a small energy gap between the conduction and valence bands of

    A
    copper
    B
    silver
    C
    sodium
    D
    aluminium

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    In a good conductor the energy gap between the conduction band and the valence band is

    In a good conductor the energy gap between the conduction band and the valence bond is

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