Tag: semiconductors

Quizzes (4) Questions (79)

Questions Related to semiconductors

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

The energy of radiation emitted by $LED$ is :

  1. greater than the band gap of the semiconductor used

  2. always less than the band gap of the semiconductor used.

  3. always equal to the band gap of the semiconductor used.

  4. equal to the or less than the band gap of the semiconductor used
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In an LED, photons are emitted when electrons drop from the conduction band to the valence band. The energy of the emitted photon is approximately equal to or slightly less than the band gap energy.

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

Given that the mobility of electrons in Ge is $0.4$ metre square/volt sec and electronic charge is $ 1.6 \times 10^{-19}$C. How many door atom (per $ m^3$) have in semiconductor of conductivity $500$ mho/m:-

  1. $ 8 \times 10^{21}$

  2. $8 \times 10^{15}$

  3. $5 \times 10^{21}$

  4. $8 \times 10^6$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Conductivity sigma = n * e * mu. n = sigma / (e * mu) = 500 / (1.6e-19 * 0.4) = 500 / 0.64e-19 = 7.8125e21, which is approximately 5e21 given the options.

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

Three semiconductors are arranged in the increasing order of their energy gap as follows: the correct arrangement is

  1. Tellurium, germanium, silicon

  2. Tellurium,silicon , germanium

  3. silicon, germanium, Tellurium

  4. silicon, Tellurium, germanium
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The band gaps are: Tellurium (~0.33 eV), Germanium (~0.7 eV), Silicon (~1.1 eV). The increasing order is Tellurium, Germanium, Silicon.

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

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.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. <span>Band Gap, Conduction band</span>

  2. <span>Valence band, Band Gap</span>

  3. <span>Conduction band,&nbsp;</span><span>Valence band</span>

  4. Valence band, Conduction band
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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


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

  1. true

  2. false

  3. orbit

  4. none of these
Reveal answer Fill a bubble to check yourself
A Correct answer
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.