Tag: energy bands

Quizzes (0) Questions (63)

Questions Related to energy bands

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

State whether True or False :

A semiconductor at absolute zero become a insulator.

  1. True

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

The conductivity and non-conductivity of material are dependent on the motion of electrons. If the motion is happening it is conductor.

Now, at absolute zero, the temperature is so low that it stops the motion of the electrons. Thus making it a complete insulator.
$\Rightarrow$  Statement (A) is the correct answer.

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

What is forbidden energy gap(Eg) or band gap?

  1. Forbidden energy gap ${ E } _{ g }$ is the difference of energy levels of conduction band and within conduction band

  2. Forbidden energy gap ${ E } _{ g }$ is the difference of energy levels of conduction band and valence band.

  3. when there is no energy

  4. conduction band
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Forbidden energy gap ${ E } _{ g }$ is the difference of energy levels of conduction band and valence band.

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

Give band gap Eg value for conductor, insulator and semiconductor?

  1. Conductor$<1MeV$, insulation $\ge 6eV$, semiconductor $\approx 8eV$.

  2. Conductor$<1MeV$, insulation $\ge 6eV$, semiconductor $\approx 1eV$.

  3. Conductor$<2MeV$, insulation $\ge 6eV$, semiconductor $\approx 1eV$.

  4. Conductor$<1MeV$, insulation $\ge 7eV$, semiconductor $\approx 1eV$.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Conductor$<1MeV$, insulation $\ge 6eV$, semiconductor $\approx 1eV$.

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.