Electronic Properties - Properties and Applications of Materials - Engineering Sciences Previous Year Questions

1

2010 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2010

The density of states (DOS), for 1 cm³ of Cu, at Fermi level per meV is

A

1.20 × 10¹⁵

B

1.80 × 10¹⁹

C

1.20 × 10²²

D

1.81 × 10²²

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2

2012 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2012

The electron concentration in an n-type semiconductor is 5 × 10¹⁸/m³. If the drift velocity of electrons is 100 m/s in an electric field of 500 V/m, calculate the conductivity of the semiconductor.

A

0.16 × 10^-1 S/m

B

1.60 × 10^-1 S/m

C

2.50 × 10^-1 S/m

D

30.05 × 10^-1 S/m

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3

2014 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2014

At room temperature, the typical barrier potential for silicon p-n junction in Volt (V) is

A

0.7x10^-23

B

0.07

C

0.70

D

7.0

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4

2014 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2014

At low injection level, a forward biased p-n junction would have

A

no charge carriers

B

minority carrier concentration much more than majority carrier concentration

C

minority carrier concentration equal to majority carrier concentration

D

minority carrier concentration much less than majority carrier concentration

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5

2014 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2014

The volume resistivity of a polymeric material is 10¹⁷ Ωm. Find the resistance (in MΩ) of a cube of the material of side 1 cm. The direction of current flow is as shown in the figure below.

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6

2015 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2015

What would be the maximum number of electron-hole pairs that can be generated using a silicon detector irradiated by x-ray of energy 1.54 keV. The band gap of silicon is 1.1 eV.

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7

2015 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2015

The slope of a graph of log_e(conductivity) versus 1/T (where T is the temperature) for an intrinsic semiconductor with energy gap E_g is

A

E_g/2k

B

−E_g/2k

C

E_g/k

D

−E_g/k

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8

2015 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2015

A capacitor has a 0.075 cm thick BaTiO₃ dielectric with a dielectric constant of 2000 and an electrode area of 0.2 cm². What is the capacitance of this capacitor in nF?

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9

2015 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2015

The correct statement with regard to electrical property of polymeric materials is

A

For non-polar materials, dielectric constant is independent of frequency & temperature

B

For polar materials, dielectric constant depends on frequency but not on temperature

C

For non polar materials, power losses are high and depend on temperature & frequency

D

For polar materials, power losses are low and independent of frequency

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10

2016 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2016

For a typical metal at room temperature and atmospheric pressure, the Fermi energy is defined as the energy level for which the probability of occupancy is:

A

0

B

0.25

C

0.5

D

1

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11

2016 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2016

In the photoelectric effect, electrons are ejected

A

at all wavelengths, as long as the intensity of the incident radiation is above a threshold value.

B

at all wavelengths, as long as the intensity of the incident radiation is below a threshold value.

C

at all intensities, as long as the wavelength of the incident radiation is below a threshold value.

D

at all intensities, as long as the wavelength of the incident radiation is above a threshold value.

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12

2017 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2017

Which of the following statement(s) is/are true
(i) All piezoelectric materials are necessarily ferroelectric
(ii) All ferroelectric materials are necessarily piezoelectric
(iii) All pyroelectric materials are necessarily piezoelectric
(iv) All pyroelectric materials are necessarily ferroelectric

A

(i) and (ii)

B

(ii) and (iii)

C

(i) and (iv)

D

(ii) and (iv)

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13

2017 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2017

Which of the following treatment(s) can increase the electrical conductivity of silicon (i) Heating (ii) Doping with arsenic (iii) Doping with aluminium (iv) Exposure to light

A

Only (i)

B

Only (i) and (ii)

C

Only (i), (ii) and (iv)

D

All (i), (ii), (iii) and (iv)

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14

2017 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2017

Copper is an FCC metal with lattice parameter of 3.62 Å. Hall effect measurement shows electron mobility to be 3.2×10³ m²V^-1s^-1. Electrical resistivity of copper is 1.7 x10^-8 Ωm. The average number of free electrons per atom in copper is ……………….(Charge of an electron: 1.6x10^-19 C)

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15

2018 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2018

An electron makes a transition from the valence band to the conduction band in an indirect band gap semiconductor. Which one of the following is true?

A

Energy of the electron decreases.

B

A photon is emitted in the process.

C

A phonon is annihilated in the process.

D

A photon is created in the process.

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16

2018 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2018

An intrinsic semiconductor has conduction electron concentration, \( n = 10^{12} \text{ cm}^{-3} \). The mobility of both electrons and holes are identical = \( 4 \times 10^4 \text{ cm}^2 \text{ V}^{-1} \text{ s}^{-1} \). If a voltage of 100 V is applied on two parallel end faces of the cube (edge length 1 cm) through Ohmic contacts, the current through the cube would be (in mA)
(Given: charge of electron = \( 1.6 \times 10^{-19} \) C)

A

640

B

1280

C

6400

D

12800

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17

2019 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2019

GaAs has advantage over silicon when used in intergrated circuits at low power because it has

A

larger band gap

B

more than one element

C

higher electron mobility

D

higher hole mobility

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18

2019 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2019

The de Broglie wavelength of an electron accelerated across a 300 kV potential in an electron microscope is ______ ×10^-12 m. Ignore relativistic effects. (round off to 2 decimal places) (Given: Planck’s constant = 6.63×10^-34 J s, electron rest mass = 9.11×10^-31 kg, electron charge = 1.6×10^-19 C)

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19

2020 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2020

Density of states, D(E), in a three dimensional solid varies with energy (E) as

A

E^{1/2}

B

E^{0}

C

E^{-1/2}

D

E^{3/2}

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20

2020 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2020

Pure silicon (Si) has a band gap (E_g) of 1.1 eV. This Si is doped with 1 ppm (parts per million) of phosphorus atoms. Si contains 5 × 10²⁸ atoms per m³ in pure form. At temperature T = 300 K, the shift in Fermi energy upon doping with respect to intrinsic Fermi level of pure Si will be ______ eV (with appropriate sign and round-off to two decimal places).
Intrinsic carrier concentration of Si, n_i, is given as:
\( n_i = 2\left(\frac{2\pi m k_B T}{h^2}\right)^{3/2} \exp\left(-\frac{E_g}{2 k_B T}\right) \)
Given:
Mass of an electron, m = 9.1 × 10^-31 kg.
Charge of an electron, e = 1.6 × 10^-19 C
Boltzmann constant, k_B = 1.38 × 10^-23 J.K^-1
Planck's constant, h = 6.6 × 10^-34 J.s^-1

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