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

1

2007 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2007

In the intrinsic region, drift mobility of electrons in a doped semiconductor as a function of temperature

A

is limited due to scattering by ionized impurities

B

is limited due to scattering by phonons

C

is limited due to scattering by point defects

D

remains unaffected

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2

2007 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2007

The equivalent conductance of the forward biased diode, with bias voltage \(V_d\) at the room temperature is

A

constant

B

proportional to \(V_d\)

C

proportional to \(V_d^2\)

D

proportional to exp (\(KV_d\))

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3

2007 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2007

Match the materials given in Group I with the applications in Group II and choose the correct matching from (A), (B), (C) and (D).
Group I (Material)
P   GaAs_1-xP_x
Q   MgB₂
R   Hydroxyapatite (HAP)
S   Kevlar^TM Fibers

Group II (Application)
1. Prosthetic applications
2. Bulletproof jackets
3. LEDs
4. Abrasives
5. Superconducting magnets

A

P-3, Q-5, R-1, S-2

B

P-3, Q-5, R-4, S-2

C

P-5, Q-4, R-1, S-2

D

P-3, Q-5, R-4, S-1

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4

2007 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2007

Assuming all impurities are ionized, the hole concentration per m^3 would be

A

2.894 x 10^-7

B

4.197 x 10^5

C

4.197 x 10^6

D

4.197 x 10^12

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5

2008 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2008

The device structure shown in the figure is that of a

A

pnp BJT

B

p-channel MOSFET

C

npn BJT

D

n-channel MOSFET

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6

2008 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2008

For the n-channel JFET shown in the figure the pinch-off voltage, \(V_p = -5\) V, and gate source voltage, \(V_{GS} = -3\) V. The minimum required drain to source voltage, \(V_{DS}\) to operate at pinch-off condition is

A

0 V

B

2 V

C

5 V

D

8 V

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7

2008 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2008

A 1 mm thick sheet of a material having a relative dielectric constant of 4 is subjected to a static voltage of 100 V. The polarization induced in the sheet is

A

3×10^-6 C.m^-2

B

2.7×10^-6 C.m^-2

C

4.2×10^-7 C.m^-2

D

6.8×10^-8 C.m^-2

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8

2008 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2008

In BaTiO3, the presence of spontaneous polarization is as a result of the

A

relative displacements of the Ti⁴⁺ and O^2- ions from their symmetrical positions

B

displacement of only cations from their symmetrical positions

C

relative displacements of Ba²⁺ and O^2- ions from their symmetrical positions

D

displacement of only O^2- ions from their symmetrical positions

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9

2008 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2008

The electrical conductivity of the semiconductor at 300 K is

A

2.04 Ω⁻¹m⁻¹

B

1.34 Ω⁻¹m⁻¹

C

0.70 Ω⁻¹m⁻¹

D

2.74 Ω⁻¹m⁻¹

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10

2008 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2008

The forward characteristics of a p-n diode is given by \(i = I_s e^{v/(nV_T)}\) with \(n = 2\), and \(V_T = 25\) mV. If the diode current is measured to be 100 mA at 0.7 V drop, the diode power dissipation at a diode current of 200 mA is

A

70 mW

B

140 mW

C

143 mW

D

147 mW

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11

2008 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2008

Match the material (Group I) with its most well known application (Group II).

Group I (Material)	Group II (Application)
P) Graphite	1) Lubricant
Q) Cermet	2) Cutting tools
R) PbS	3) Infrared detector
S) Quartz	4) Crystal oscillator
	5) Red LED

A

P-1, Q-2, R-3, S-4

B

P-3, Q-1, R-2, S-4

C

P-5, Q-1, R-2, S-3

D

P-2, Q-5, R-1, S-4

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12

2008 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2008

Upon increasing the temperature to 373 K, the electrical conductivity increases to 25.75 Ω⁻¹m⁻¹. The bandgap of the semiconductor is

A

1.43 eV

B

1.11 eV

C

0.67 eV

D

0.33 eV

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13

2009 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2009

During indirect intra-band transition, electrons undergo

A

change in energy and momentum

B

change in momentum but no change in energy

C

change neither in energy nor in momentum

D

change in energy but no change in momentum

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14

2009 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2009

Correlate the material properties given in Column I with the units given in Column II.

Column I
P. Magnetic moment
Q. Thermal conductivity
R. Fracture toughness
S. Electron mobility

Column II
1. MN m^-3/2
2. H m^-1
3. A m²
4. m² V^-1 s^-1
5. J s^-1 m^-1 K^-1

A

P-2, Q-5, R-1, S-4

B

P-4, Q-5, R-1, S-3

C

P-3, Q-5, R-1, S-4

D

P-3, Q-2, R-4, S-1

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15

2009 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2009

A potential of 10 volts is applied across a parallel plate capacitor which has a plate area of \(10^{-4}\) m² and a plate separation of \(2 \times 10^{-3}\) m. If dielectric constant of the material placed between parallel plates is 10, the capacitance and the magnitude of the charge stored between the plates will be

A

\(4.425 \times 10^{-13}\) F and \(4.425 \times 10^{-12}\) C

B

\(8.850 \times 10^{-13}\) F and \(8.850 \times 10^{-12}\) C

C

\(4.425 \times 10^{-12}\) F and \(4.425 \times 10^{-11}\) C

D

\(8.850 \times 10^{-12}\) F and \(8.850 \times 10^{-11}\) C

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16

2009 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2009

Conductivity of Silicon at 300 K is \(3.16 \times 10^{-4}\) ohm⁻¹ m⁻¹ and that of Germanium is \(2.12\) ohm⁻¹ m⁻¹ at 300 K. At what temperature would the conductivity of intrinsic Silicon be the same as the conductivity of intrinsic Germanium at 300 K ? (Given: \(E_g\) of Silicon at 300 K = 1.12 eV, \(E_g\) of Germanium at 300 K = 0.72 eV)

A

\(\sim 506\) K

B

\(\sim 606\) K

C

\(\sim 726\) K

D

\(\sim 816\) K

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17

2009 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2009

The value of activation energy (J mol⁻¹) of lithium diffusion in silicon is

A

66086

B

66986

C

67086

D

67986

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18

2009 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2009

The value of jump frequency factor of lithium in silicon in m² s⁻¹ is

A

2.15 × 10⁻⁷

B

3.15 × 10⁻⁷

C

3.15 × 10⁻⁸

D

2.15 × 10⁻⁸

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19

2009 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2009

The number of free electrons per m³ of Aluminum at 300 K is

A

6.05 × 10²⁸

B

7.05 × 10²⁸

C

6.05 × 10²⁷

D

7.05 × 10²⁷

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20

2009 · Engineering Sciences · Properties and Applications of Materials · Electronic Properties

Engineering Sciences (XE) 2009

The conductivity of aluminum (ohm⁻¹ m⁻¹) at 300 K is

A

3.40 × 10⁶

B

4.40 × 10⁶

C

3.40 × 10⁷

D

4.40 × 10⁷

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