Physics

CSET3101B.Tech CSE2022-26

Mahatma Gandhi Central University, Bihar

B.Tech Computer Science & Engineering

Semester 1 Examination, 2022

Physics (CSET3101)

Faculty: Ms. AparnaMaximum Marks: 95

Assessment Questions

Physics (CSET3101) - 2022

SECTION – A

(MULTIPLE CHOICE QUESTIONS for 10 Marks). Attempt all questions. Each question carries one mark.

1
The velocity of non-relativistic free electrons in three-dimensional metal, at $T = 0$ is (density of electrons is $n$ )
2
In Drude model, the only possible interaction of a free electron with its environment is via instantaneous-
3
The energy wave vector dispersion relation for one dimensional crystal lattice constant $a$ using the tight binding model is $E(k) = E_v - \beta - \gamma \cos(ka)$ . The effective mass of electron at the top of the band is -
4
The lowest quantum mechanical energy of a particle confined in a one-dimensional box of size $L$ is $2 eV$ . The energy of the quantum mechanical ground state for a system of three non-interacting spin $\frac{1}{2}$ particles is-
5
In the Kronig-Penney model, the discontinuities in $E$ versus $k$ curve occur for-
6
A metal-semiconductor junction diode is called-
7
An intrinsic semiconductor with mass of a hole $m_h$ and mass of an electron $m_e$ is at a finite temperature $T$ . If the top of the valence band energy is $E_v$ and the bottom of the conduction band energy is $E_c$ , the Fermi energy of the semiconductor is -
8
The temperature dependence of the electrical conductivity $\sigma$ of two intrinsic semiconductors $A$ and $B$ is shown in the figure. If $E_A$ and $E_B$ are the band gaps of $A$ and $B$ respectively, which one of the following is TRUE?
9
What is an exciton?
10
During the collection of e-h pairs, holes are collected by-

SECTION – B

Short Answer Questions - 20 Marks. Attempt ANY FOUR questions out of six questions. Each question carries 5 Marks.

1
Derive the expression for density of states of nanowire.
2
State law of mass action for intrinsic semiconductors. Calculate the hole and electron concentration in p-type semiconductor if the acceptor density is $2 \times 10^{20}$ atoms/m³ and intrinsic concentration is $4.0 \times 10^{19}$ per m³ at $300 \degree{C}$ .
3
Why is it not possible to image the nano objects with infrared or X-rays? What are the current capabilities with these techniques? What are their specific advantages?
4
Define the term “effective mass of an electron.” Is it different from the free electron mass? What is the significance? Discuss the conditions when the effective mass of an electron becomes positive, negative, and infinite.
5
Define the following terms

(i) Recombination

(ii) Block function

(iii) Fermi function

(iv) Direct and Indirect band gap
6
Give a brief discussion on the four probe measurement technique for resistivity measurement.

SECTION – C

Long Answer Questions - 30 Marks. Attempt ALL questions having internal choices. The question carries 10 marks.

1
Answer any ONE of the following
(a)
Solve the Schrödinger's wave equation for a particle in 1-D rigid potential box of length $a$ and having the potential energy as follows $V(x) = \begin{cases} \infty, & \text{for } x < 0 \text{ and } x > a \\ 0, & \text{for } 0 < x < a \end{cases}$ . Calculate the probability of finding the particle in the region $\frac{a}{4} \leq x \leq \frac{3a}{4}$ .
OR
(b)
What are the main conclusions of the Kronig-Penney model? Draw schematically the energy wavevector diagram for the crystal. The energy wavevector dispersion relation for a 1-dimensional crystal of lattice constant a is given by $E = E_0 + A sin^2(\frac{ka}{2})$ , where $E_0$ and $A$ are constant. Find the group velocity and effective mass of an electron at the second Brillouin zone boundary.
2
Answer any ONE of the following
(a)
Write about the classification of different synthesis routes of nanoparticles. Discuss any one of the physical/chemical methods to synthesize the nanostructured materials.
OR
(b)
Give a brief discussion on the Scanning electron microscope (SEM) or X-ray diffraction (XRD) characterization technique.
3
Answer any ONE of the following
(a)
Draw the energy band-diagram of a metal n-type semiconductor interface for the case $φm < φs$ , where $φ$ denotes the workfunction of material and discuss the charge transport mechanism across the interface in detail under different biasing conditions.
OR
(b)
Write short notes on the followings

(i) Photovoltaic device

(ii) Tauc’s relation for band gap calculation

(iii) Fermi energy,

(iv) Exciton

(v) Shortcomings of free electron gas model

End of Question Paper