# Multiple choice question for engineering

## Set 1

1. The conduction band edge in the p material is not at the same level to that of conduction band edge in the n material. Is it true or false?

a) True

b) False

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2. Which of the following equations represent the correct expression for the shift in the energy levels for the p-n junction?

a) E_{o} = E_{cn} – E_{cp}

b) E_{o} = E_{cp} – E_{cn}

c) E_{o} = E_{cp} + E_{cn}

d) E_{o} = -E_{cp} – E_{cn}

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3. Calculate the E_{o} given that N_{d}=1.5*10^{10}cm^{-3}, N_{a}=1.5*10^{10}cm^{-3} at temperature 300K?

a) 1.5*10^{10}eV

b) 0.256eV

c) 0eV

d) 4.14*10^{-21}eV

### View Answer

_{o}=kTln((N

_{d}*N

_{a})/(n

_{i})

^{2}) Substituting k=1.38*10

^{-23}/K, T=300k and the values ofN

_{d},N

_{a}and ni, We get E

_{o}=0eV.

4. In a p-n junction, the valence band edge of the p material is greater than which of the following band?

a) Conduction band edge of n material

b) Valence band edge of n material

c) Conduction band edge of p material

d) Fermi level of p material

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5. Which of the following equations represent the correct expression for the band diagram of the p-n junction? (E1=difference between the fermi level of material and conduction band of n material and E2=difference between the conduction band of n material and fermi level of n material)

a) E_{cn} – E _{f} = (1/2)*E_{G} – E_{1}

b) E_{cn} – E _{f} = (1/2)*E_{G} – E_{2}

c) E_{f} – E_{cp} = (1/2)*E_{G} – E_{1}

d) E_{cn} – E_{f} = (1/2)*E_{G} + E_{1}

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6. Calculate the value of E_{o} when p_{no}=10^{4}cm^{-3} and p_{po}=10^{16}cm^{-3} at T=300K.

a) 1meV

b) 0.7meV

c) 0.7eV

d) 0.1meV

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_{o}=kTln(p

_{po}/p

_{no}) Substituting the values, we get E

_{o}=0.7eV.

7. Calculate the value of Dp when µp=400cm/s and V_{T}=25mV.

a) 1

b) 0.01

c) 0.1

d) 10

### View Answer

_{T}=400*10

^{-2}*25*10

^{-3}=0.1.

8. What is the value of kT at room temperature?

a) 0.0256eV

b) 0.25eV

c) 25eV

d) 0.0025eV

### View Answer

^{-23}*300K =4.14*10

^{-21}/ (1.6*10

^{-19}) =0.0256eV.

9. Is Vo depends only on the equilibrium concentrations. Is it true or false?

a) True

b) False

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10. Calculate Vo when p_{po}=10^{16}cm^{-3}, p_{no}=10^{4}cm^{-3} and Vt=25mV.

a) 69V

b) 6.9V

c) 0.69V

d) 0.069V

### View Answer

_{o}=V

_{T}ln(p

_{po}/p

_{no}) =25*10

^{-3}*ln(10

^{16}/10

^{4}) =0.69V.

## Set 2

1. Which states get filled in the conduction band when the donor-type impurity is added to a crystal?

a) Na

b) Nd

c) N

d) P

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2. Which of the following expression represent the correct formulae for calculating the exact position of the Fermi level for p-type material?

a) E_{F} = E_{V} + kTln(N_{D} / N_{A} )

b) E_{F} = -E_{V} + kTln(N_{D} / N_{A} )

c) E_{F} = E_{V} – kTln(N_{D} / N_{A} )

d) E_{F} = -E_{V} – kTln(N_{D} / N_{A} )

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3. Where will be the position of the Fermi level of the n-type material when N_{D}=N_{A}?

a) Ec

b) Ev

c) Ef

d) Efi

### View Answer

_{D}=N

_{A}, kTln(N

_{D}/N

_{A})=0 So, Ef=Ec.

4. When the temperature of either n-type or p-type increases, determine the movement of the position of the Fermi energy level?

a) Towards up of energy gap

b) Towards down of energy gap

c) Towards centre of energy gap

d) Towards out of page

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5. Is it true, when the temperature rises, the electrons in the conduction band becomes greater than the donor atoms?

a) True

b) False

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6. If the excess carriers are created in the semiconductor, then identify the correct energy level diagram.

a)

b)

c)

d)

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7. If excess charge carriers are created in the semiconductor then the new Fermi level is known as Quasi-Fermi level. Is it true?

a) True

b) False

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8. Ef lies in the middle of the energy level indicates the unequal concentration of the holes and the electrons?

a) True

b) False

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9. Consider a bar of silicon having carrier concentration n0=10^{15} cm^{-3} and ni=10^{10}cm^{-3}. Assume the excess carrier concentrations to be n=10^{13}cm^{-3}, calculate the quasi-fermi energy level at T=300K?

a) 0.2982 eV

b) 0.2984 eV

c) 0.5971 eV

d) 1Ev

### View Answer

^{-23}*300*ln(10

^{13}+10

^{15}/10

^{13}) =0.2984 eV.

10. From the above equation, assuming the same values for the for ni, n= p and T. Given that p0=10^{5}cm^{-3}. Calculate the quasi-fermi energy level in eV?

a) 0.1985

b) 0.15

c) 0.1792

d) 0.1

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Substituting the respective values,
E_{Fi} – E_{Fp}=0.1792 eV.

## Set 3

(Q.1-Q.3) A parallel resonant circuit has a resistance of 2k ohm and half power frequencies of 86 kHz and 90 kHz.

1. The value of capacitor is

a) 6 µF

b) 20 nF

c) 2 nF

d) 60 µF

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2. The value of inductor is

a) 4.3 mH

b) 43 mH

c) 0.16 mH

d) 1.6 mH

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^{(0.5)}or L = 0.16 mH.

3. The quality factor is

a) 22

b) 100

c) 48

d) 200

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(Q.4-Q.5) A parallel resonant circuit has a midband admittance of 25 X 10^{(-3)} S, quality factor of 80 and a resonant frequency of 200 krad s.

4. The value of R (in ohm) is

a) 40

b) 56.57

c) 80

d) 28.28

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5. The value of C is

a) 2 µF

b) 28.1 µF

c) 10 µF

d) 14.14 µF

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6. A parallel RLC circuit has R 1 k and C 1 F. The quality factor at resonance is 200. The value of inductor is

a) 35.4 H

b) 25 H

c) 17.7 H

d) 50 H

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^{0.5}.

7. A parallel circuit has R = 1k ohm , C = 50 µF and L = 10mH. The quality factor at resonance is

a) 100

b) 90.86

c) 70.7

d) None of the above

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^{0.5}.

8. A series resonant circuit has L = 1 mH and C = 10 F. The required R (in ohm) for the BW = 15 9 . Hz is

a) 0.1

b) 0.2

c) 0.0159

d) 500

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9. For the RLC parallel resonant circuit when R = 8k, L = 40 mH and C = 0.25 F, the quality factor

Q is

a) 40

b) 20

c) 30

d) 10

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^{0.5}.

10. A series resonant circuit has an inductor L = 10 mH. The resonant frequency w = 10^6 rad/s and bandwidth is BW = 10^{3} rad/s. The value of R and C will be

a) 100 F, 10 ohm

b) 100 pF, 10 ohm

c) 100 pF, 10 Mega-ohm

d) 100 µF, 10 Meg-ohm

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## Set 4

1. Consider a voltage amplifier having a frequency response of the low-pass STC type with a dc gain of 60 dB and a 3-dB frequency of 1000 Hz. Then the gain db at

a) f = 10 Hz is 55 db

b) f = 10 kHz is 45 db

c) f = 100 kHz is 25 db

d) f = 1Mhz is 0 db

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2. STC networks can be classified into two categories: low-pass (LP) and high-pass (HP). Then which of the following is true?

a) HP network passes dc and low frequencies and attenuate high frequency and opposite for LP network

b) LP network passes dc and low frequencies and attenuate high frequency and opposite for HP network

c) HP network passes dc and high frequencies and attenuate low frequency and opposite for LP network

d) LP network passes low frequencies only and attenuate high frequency and opposite for HP network

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3. Single-time-constant (STC) networks are those networks that are composed of, or can be reduced to

a) One reactive component (L or C) and a resistance (R)

b) Only capacitive component (C) and resistance (R)

c) Only inductive component (L) and resistance (R)

d) Reactive components (L, C or both L and C) and resistance (R)

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4. The signal whose waveform is not effected by a linear circuit is

a) Triangular Waveform signal

b) Rectangular waveform signal

c) Sine/Cosine wave signal

d) Sawtooth waveform signal

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5. Which of the following is not a classification of amplifiers on the basis of their frequency response?

a) Capacitively coupled amplifier

b) Direct coupled amplifier

c) Bandpass amplifier

d) None of the mentioned

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6. General representation of the frequency response curve is called

a) Bode Plot

b) Miller Plot

c) Thevenin Plot

d) Bandwidth Plot

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7. Under what condition can the circuit shown be called a compensated attenuator.

a) C1R1 = C2R2

b) C1R2 = C2R1

c) C1C2 = R1R2

d) R1 = 0

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8. When a circuit is called compensated attenuator?

a) Transfer function is directly proportional to the frequency

b) Transfer function is inversely proportional to the frequency

c) Transfer function is independent of the frequency

d) Natural log of the transfer function is proportional to the frequency

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9. Which of the following is true?

a) Coupling capacitors causes the gain to fall off at high frequencies

b) Internal capacitor of a device causes the gain to fall off at low frequencies

c) All of the mentioned

d) None of the mentioned

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10. Which of the following is true?

a) Monolithic IC amplifiers are directly coupled or dc amplifiers

b) Televisions and radios use tuned amplifiers

c) Audio amplifiers have coupling capacitor amplifier

d) All of the mentioned

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## Set 5

1. What is the range of the carrier lifetime?

a) Nanoseconds to microseconds

b) Nanoseconds to hundreds of microseconds

c) Nanoseconds to tens of microseconds

d) Nanoseconds to milliseconds

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2. What is the process number of Schokley-Read-Hall Theory processes?

Process-‘ The capture of an electron from the conduction band by an initially neutral empty trap’

a) Process1

b) Process2

c) Process3

d) Process4

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3. Calculate the recombination rate if the excess carrier concentration is 10^{14}cm^{-3} and the carrier lifetime is 1µseconds.

a) 10^{8}

b) 10^{10}

c) 10^{20}

d) 10^{14}

### View Answer

^{14}/ 10

^{-6}R=10

^{20}.

4. Calculate the capture rate where Cn=10, Nt=10^{10}cm^{-3}, n=10^{20} and f_{F} (Et)=0.4.

a) 6*10^{30 }

b) 5*10^{30}

c) 36*10^{30}

d) 1.66*10^{29}

### View Answer

_{cn}=C

_{n}*N_t*(1-f

_{F}(Et))*n Substituting the values, R

_{cn}=6*10

^{30}.

5. Calculate the emission rate where En=2.5, Nt=10^{10}cm^{-3} and f_{F} (Et)=0.6 .

a) 15*10^{10}

b) 1.5*10^{10}

c) 15*10^{11}

d) 1.5*10^{11}

### View Answer

_{en}=E

_{n}*N

_{t}*(f

_{F}(Et)) Substituting the values, R

_{en}=1.5*10

^{10}.

6. At what condition, the rate of electron capture from the conduction band and the rate of the electron emission back into the conduction band must be equal?

a) Thermal equilibrium

b) At room temperature

c) T=250K

d) At boiling temperature

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7. Calculate the carrier lifetime when Cp=5 and Nt=10^{10}cm^{-3}.

a) 2*10^{11}

b) 2*10^{-11}

c) 20*10^{-11}

d) 20*10^{11}

### View Answer

_{p}=1/(C

_{p}*N

_{t}) =1/(5*10

^{10}) =2*10

^{-11}.

8. The number of majority carriers that are available for recombining with excess minority carriers decreases as the excess semiconductor becomes intrinsic. Is it true?

a) True

b) False

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9. Which of the following is used as the recombination agent by semiconductor device manufactures?

a) Silver

b) Gold

c) Platinum

d) Aluminium

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10. The rate of change of the excess density is proportional to the density. Is it true of false?

a) True

b) False