Tag: energy bands

Questions Related to energy bands

Depletion layer consists of:

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. electrons

  2. protons

  3. mobile ions

  4. immobile ions

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Correct Option: D

The band gap for a pure semi-colour is $2.1\ eV$. The maximum wavelength of a photon which is able to create a hole-electron pair is:

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. $600\ nm$

  2. $589\ nm$

  3. $400\ nm$

  4. $none\ of\ these$

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Correct Option: B

State whether true or false:

The highest occupied energy band is called the valence band and the lowest unoccupied energy band is called the conduction band.

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. True

  2. False

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Correct Option: A
Explanation:

The highest occupied energy band is called the valence band and the lowest unoccupied energy band is called the conduction band.
Their difference determines the conductivity of the compound.

The highest occupied energy band is called ________ and lowest unoccupied energy band is called the _________ .

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. Band Gap, Conduction band

  2. Valence band, Band Gap

  3. Conduction band, Valence band

  4. Valence band, Conduction band

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Correct Option: C
Explanation:

The highest energy band occupied by electrons is the valence band. In a conductor, the valence band is partially filled, and since there are numerous empty levels, the electrons are free to move under the influence of an electric field; thus, in a metal the valence band is also the conduction band. The valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature, while the conduction band is the lowest range of vacant electronic states. This distinction is meaningless in metals as the highest band is partially filled, taking on the properties of both the valence and conduction bands.


In metals, the conduction bands are incompletely filled orbitals that allow electrons to flow.

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. true

  2. false

  3. orbit

  4. none of these

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Correct Option: A
Explanation:

In metals, the conduction bands are incompletely filled orbitals that allow electrons to flow. This helps in electrical conductivity. If the conduction band is completely filled, then there is no flow of electrons and the conductor becomes insulator.

The highest energy band which is filled at zero Kelvin is called ________.

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. conduction band

  2. valence band

  3. insulation band

  4. filled band

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Correct Option: B
Explanation:

At zero Kelvin, all the electrons are present in valence band while conduction band is empty. So valence band is the highest energy band which is filled at zero kelvin.

If the energy gap of a semiconductor is 1.1 e V it would be:

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. Transparent to the ultraviolet radiation

  2. Opaque to the visible light

  3. Transparent to the visible light

  4. None of these

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Correct Option: B
Explanation:

Visible light lies in the range of about 2.0 eV to 3.2 eV on the electromagnetic spectrum. 

This energy is sufficient to excite the valence electrons in the semiconductor and is hence absorbed by it. 
As a result, photons of lower energy are emitted which do not fall in the visible range of light. 
This causes the opacity of the semiconductor to visible light.

Which of the following statement(s) is/are correct: 

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. The gap between the top of the valance band and the bottom of the conduction band is called energy band gap

  2. More band gap results in less electron transfer

  3. A semiconductor is a material with a small but non-zero band gap that behaves as an insulator at absolute zero

  4. All of the above

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Correct Option: D
Explanation:
In a material the gap between top of the valance band and bottom of the conduction band is called energy gap as the energy equal to this gap is required for the valance electrons to jump into conduction band.

When the band gap is high, it means it is difficult for the valance electrons to jump into conduction band i.e. higher energy is required for the electrons to enter into conduction band. This results in less electrons transfer.

A semiconductor is a material with small band gap which can fulfilled by some special treatment. At absolute zero temperature, the valance electrons don't have energy to cross this energy gap therefore semiconductors behave as insulators.

Fill in the blank.
Energy band gap size for insulators is in the range ________ eV. 

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. $1-2$

  2. $2-3$

  3. $3-4$

  4. $>4$

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Correct Option: C

In the bandgap between valence band and conduction band in a material is $5.0eV$, then the material is

physics semiconductors band theory of solids, a brief introduction electron energies in solids energy bands

  1. semiconductor

  2. good conductor

  3. superconductor

  4. insulator

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Correct Option: D
Explanation:

For an insulator, the band gap i.e. the energy difference between valence and conduction band is high i.e. $5-6$ eV.