Semiconductor Devices and Logic Gates · Physics · COMEDK

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MCQ (Single Correct Answer)

1

The zener voltage in the circuit shown is $\mathrm{V}_{\mathrm{Z}}=20 \mathrm{~V}$. The load resistance $\mathrm{R}_{\mathrm{L}}=5 \mathrm{k} \Omega$ and the resistance $\mathrm{R}_{\mathrm{S}}=10 \mathrm{k} \Omega$. If the input voltage is $\mathrm{V} \mathrm{s}=100 \mathrm{~V}$, then the current through the zener diode in milliampere is:

COMEDK 2025 Evening Shift Physics - Semiconductor Devices and Logic Gates Question 1 English

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2
What is the dc component of the output voltage if a sinusoidal signal of 33 V peak voltage is the input of a half wave diode rectifier circuit?
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3
An intrinsic semiconductor has equal concentrations of hole and electron which is equal to $4 \times 10^8 \mathrm{~m}^{-3}$. During its conversion to extrinsic semiconductor, concentration of hole increases to $8 \times 10^{10} \mathrm{~m}^{-3}$. The new electron concentration is:
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4

COMEDK 2025 Afternoon Shift Physics - Semiconductor Devices and Logic Gates Question 4 English

Three ideal diodes and resistors connected to the cell of negligible internal resistance is as shown. Find the current passing through the $10 \Omega$ resistor.

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5
Diamond is considered as an insulator because
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6
What is the maximum wave length of EM radiation required to move an electron from the valance band to conduction band of a semiconductor? [Given :Energy gap $\mathrm{E}_{\mathrm{g}}=1.98 \times 10^{-19} \mathrm{~J}$; Planck's constant $h=6.6 \times 10^{-34} \mathrm{Js}$ ]
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7
A Si and a Ge diode has identical physical dimensions. The band gap in Si is larger than that in Ge. On applying identical reverse bias across these diodes,
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8
The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than $1.24 \mu \mathrm{~m}$ is incident on it. The band gap (in eV ) for the semiconductor is
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9

In the energy band diagram of a material shown below, open circles and filled circles denote holes and electrons respectively. The material is a

COMEDK 2025 Morning Shift Physics - Semiconductor Devices and Logic Gates Question 7 English

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10

The conductivity of a semiconductor increases with increase in temperature because

A) number density of free current carriers increases

B) relaxation time increases

C) both number density of carriers and relaxation time increase

D) number density of current carriers increases, relaxation time decreases but effect of decrease in relaxation time is much less than increase in number density

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11

COMEDK 2024 Evening Shift Physics - Semiconductor Devices and Logic Gates Question 11 English

The output of the given circuit is

A. Negatively rectified half wave

B. Positively rectified half wave

C. Negatively rectified full wave

D. Zero all times

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12

The following are the graphs of potential barrier versus width of the depletion region for a p-n junction diode.

COMEDK 2024 Evening Shift Physics - Semiconductor Devices and Logic Gates Question 10 English

Which of the following is correct?

I II III IV`
A - unbiased diode A - Forward biased diode A - unbiased diode A - unbiased diode
B - Reverse biased B - Reverse biased B - Forward biased B - unused diode
C - Forward biased C - unbiased C - Reverse biased C - Forward biased

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13

$$ \text { In a p-n junction, the depletion layer of thickness } 1 \mu \mathrm{m} \text { has } 0.05 \mathrm{~V} \text { potential across it. The electric field in } N C^{-1} \text { is } $$

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14

The mobility of the charge carriers increases with

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15

In intrinsic semiconductors at room temperature, number of electrons and holes are

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16

A semiconductor $$\mathrm{X}$$ is made by doping silicon with phosphorous. A second semiconductor $$\mathrm{Y}$$ is made by doping silicon with aluminium. The two are joined by a suitable technique to form a $$\mathrm{p}$$-$$\mathrm{n}$$ junction and is connected to a battery such that $$\mathrm{Y}$$ is joined to negative of the battery and $$\mathrm{X}$$ to the positive of the battery. Which of the following statements is correct?

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17

In a given semiconductor, the ratio of the number density of electron to number density of hole is $$2: 1$$. If $$\frac{1}{7}$$th of the total current is due to the hole and the remaining is due to the electrons, the ratio of the drift velocity of holes to the drift velocity of electrons is :

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18

An ideal diode is connected in series with a capacitor. The free ends of the capacitor and the diode are connected across a $$220 \mathrm{~V}$$ ac source. Now the potential difference across the capacitor is :

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19

Though $$\mathrm{Sn}$$ and $$\mathrm{Si}$$ are $$4^{\text {th }}$$ group elements, $$\mathrm{Sn}$$ is a metal while $$\mathrm{Si}$$ is a semiconductor because

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20

A transistor is connected in CE configuration. The collector supply is $$10 \mathrm{~V}$$ and the voltage drop across a resistor of $$1000 \Omega$$ in the collector circuit is $$0.5 \mathrm{~V}$$. If the current gain factor is 0.96 , then the base current is

COMEDK 2023 Morning Shift
21

Which logic gate is represented by the following combination logic gates?

COMEDK 2023 Morning Shift Physics - Semiconductor Devices and Logic Gates Question 25 English

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22

An LED is constructed from a $$p$$-$$n$$ junction diode using GaAsP. The energy gap is $$1.9 \mathrm{~eV}$$. The wavelength of the light emitted will be equal to

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23

The energy gap between valance band and the conduction band for a given material is $$6 \mathrm{~eV}$$, then the material is :

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24

In the given circuit the diode $$D_1$$ and $$D_2$$ have the forward resistance $$25 \Omega$$ and infinite backward resistance. When they are connected to the source as shown, the current passing through the $$175 \Omega$$ resistor is:

COMEDK 2023 Evening Shift Physics - Semiconductor Devices and Logic Gates Question 20 English

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25

The reverse current in the semiconductor diode changes from $$20 \mu \mathrm{A}$$ to $$40 \mu \mathrm{A}$$ when the reverse potential is changed from $$10 \mathrm{~V}$$ to $$15 \mathrm{~V}$$, then the reverse resistance of the junction diode will be :

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26

For CE transistor amplifier, the audio signal voltage across the collector resistance of 4 k$$\Omega$$ is 5 V. If the current amplification factor of the transistor is 100 and base resistance is 2 k$$\Omega$$, then input signal voltage is

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27

Which of the following gate give the similar output as the output of circuit diagram shown in the figure?

COMEDK 2022 Physics - Semiconductor Devices and Logic Gates Question 28 English

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28

Choose the incorrect statements.

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29

Find the logic gate, when both the inputs are high but the output is low and vice-versa.

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30

What is the minimum band-gap of the LED diode?

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31

When a $$p$$-$$n$$ junction diode is connected in forward bias, its barrier potential

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