# Semiconductor Electronics: Materials, Devices And Simple Circuits

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| By Tanmay Shankar
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Tanmay Shankar
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Time: 30 Minute

• 1.

### What is the possible number of crystal system?

• A.

5

• B.

7

• C.

14

• D.

16

B. 7
Explanation
There are seven possible crystal systems: cubic, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal, and rhombohedral. Each crystal system is defined by the symmetry of the crystal lattice and the angles between its crystallographic axes.

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• 2.

### With fall of temperature, the forbidden energy gap of a semiconductor:

• A.

Increases

• B.

Decreases

• C.

Remains unchanged

• D.

Sometimes increases and sometimes decreases

C. Remains unchanged
Explanation
The forbidden energy gap of a semiconductor refers to the energy range that electrons cannot occupy. It is determined by the material's properties and temperature. In a semiconductor, as the temperature decreases, the atoms vibrate less, causing the forbidden energy gap to remain unchanged. This is because the energy required for an electron to move from the valence band to the conduction band remains the same, regardless of temperature. Therefore, the correct answer is that the forbidden energy gap of a semiconductor remains unchanged with the fall of temperature.

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• 3.

### What would be the fundamental frequency in the ripple, if a half wave rectifier circuit is being operated from a 50 Hz mains frequency?

• A.

25 Hz

• B.

50 Hz

• C.

70.7 Hz

• D.

100 Hz

B. 50 Hz
Explanation
The fundamental frequency in a ripple of a half wave rectifier circuit is the same as the mains frequency. In this case, the circuit is being operated from a 50 Hz mains frequency, so the fundamental frequency in the ripple would also be 50 Hz.

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• 4.

### At absolute zero, Si acts as a:

• A.

Non - metal

• B.

Metal

• C.

Insulator

• D.

None of these

C. Insulator
Explanation
At absolute zero, Si (silicon) acts as an insulator. This is because at absolute zero temperature, all thermal energy is removed from the material, causing the atoms to come to a complete stop. In the case of silicon, its valence electrons are tightly bound to the atoms and not able to move freely. This lack of mobility prevents the flow of electric current, making silicon behave as an insulator rather than a conductor.

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• 5.

### What is the equivalent resistance of the circuit across AB?

• A.

• B.

• C.

• D.

Explanation
The equivalent resistance of the circuit across AB can be either 4 Î© or 13 Î©. This is because the circuit consists of two resistors in parallel, one with a resistance of 4 Î© and the other with a resistance of 13 Î©. When resistors are connected in parallel, the total resistance is given by the formula 1/RTotal = 1/R1 + 1/R2. In this case, 1/RTotal = 1/4 + 1/13, which simplifies to RTotal = 4 Î© or 13 Î©.

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• 6.

### The graph shown represents the I – V characteristics of a Zener diode. Which part according to you operates as a voltage regulator?

• A.

Ab

• B.

Bc

• C.

Cd

• D.

De

D. De
Explanation
In the given graph, the part "de" represents the voltage regulator region of the Zener diode. In this region, the diode operates in the reverse breakdown region, where a small change in voltage results in a large change in current. This characteristic allows the Zener diode to maintain a constant voltage across its terminals, acting as a voltage regulator.

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• 7.

### For a transistor if the parameters β = 99, then the value of parameter α is:

• A.

0.9

• B.

0.99

• C.

1

• D.

9

B. 0.99
Explanation
The value of parameter Î± in a transistor is given by the formula Î± = Î² / (1 + Î²). In this case, Î² is given as 99. Plugging in the value, we get Î± = 99 / (1 + 99) = 99 / 100 = 0.99. Therefore, the correct answer is 0.99.

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• 8.

### In the ratio of concentration of electrons that of holes in a semiconductor is 7/5 and the ratio of currents is 7/4 then what is the ratio of their drift velocity?

• A.

4/7

• B.

5/8

• C.

4/5

• D.

5/4

D. 5/4
Explanation
The ratio of the concentration of electrons to holes in a semiconductor is 7/5, and the ratio of currents is 7/4. This implies that there are more electrons than holes in the semiconductor, and the current carried by electrons is greater than that carried by holes. Since drift velocity is directly proportional to current, the ratio of their drift velocities can be determined by the ratio of their currents. The ratio of currents is 7/4, which means that the drift velocity of electrons is 7/4 times that of holes. Therefore, the ratio of their drift velocities is 7/4, which is equivalent to 5/4.

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• 9.

### What will be the output voltage of the amplifier, if in an npn transistor at common emitter configuration the current gain is given as β = 100.

• A.

10-3 V

• B.

10-1 V

• C.

100 V

• D.

10 V

C. 100 V
Explanation
In a common emitter configuration, the output voltage of the amplifier is determined by the current gain of the npn transistor. The current gain, represented by Î², is given as 100. This means that for every 1 unit of input current, the transistor will produce an output current that is 100 times larger. Since the output voltage is directly proportional to the output current, the output voltage will also be 100 times larger than the input voltage. Therefore, the correct answer is 100 V.

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• 10.

### In the given figure, the current through the Zener diode is:

• A.

10 mA

• B.

6.67 mA

• C.

5 mA

• D.

3.33 mA

D. 3.33 mA
Explanation
The correct answer is 3.33 mA because the Zener diode is connected in parallel with the resistor, which creates a parallel circuit. In a parallel circuit, the current is divided among the different branches based on their resistance. Since the Zener diode has a lower resistance compared to the resistor, it will draw more current. The total current through the circuit is 10 mA, so the current through the Zener diode can be calculated using the formula: Current through Zener diode = Total current * (Resistance of Zener diode / Total resistance). Plugging in the values, we get: Current through Zener diode = 10 mA * (5 Î© / (5 Î© + 10 Î©)) = 3.33 mA.

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• 11.

### The relation between α and β parameters of a transistor is given by:

D.
Explanation
The relation between Î± and Î² parameters of a transistor is given by Î² = Î± / (1 - Î±). This equation represents the relationship between the current gain factor Î² and the common base current gain factor Î± in a transistor. It shows that Î² is directly proportional to Î±, but also depends on the reciprocal of (1 - Î±). This equation is important in transistor analysis and design, as it allows for the calculation of one parameter based on the value of the other.

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• 12.

### In the figure of the circuit the output y becomes zero for the inputs:

• A.

A = 1, B = 0, C = 0

• B.

A = 0, B = 1, C = 1

• C.

A = 0, B = 0, C = 0

• D.

A = 1, B = 1, C = 0

D. A = 1, B = 1, C = 0
Explanation
When A = 1, B = 1, and C = 0, the output y becomes zero.

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• 13.

### The figure shows a logic gate circuit with two inputs A and B and the output Y. The voltage waveforms of A, B and Y are given: The logic gate is:

• A.

NAND Gate

• B.

OR Gate

• C.

AND Gate

• D.

NOR Gate

A. NAND Gate
Explanation
Based on the given voltage waveforms, we can observe that the output Y is low (0) only when both inputs A and B are high (1). This behavior is consistent with the logic of a NAND gate, which produces a low output only when both inputs are high. Therefore, the correct answer is a NAND gate.

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• 14.

### The circuit diagram shows a logic combination with the states of outputs X, Y and Z given for inputs P, Q, R and S all at state 1. When input P and R change to state 0 with inputs Q and S still at 1, the states of outputs X, Y and Z change to:

• A.

1, 0, 0

• B.

0, 1, 0

• C.

0, 0, 1

• D.

0, 1, 1

B. 0, 1, 0
Explanation
When input P and R change to state 0 while inputs Q and S remain at 1, the circuit diagram indicates that the states of outputs X, Y, and Z change to 0, 1, and 0 respectively.

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• 15.

### Two ideal diodes are connected to a battery as shown in the figure. The current supplied by the battery is:

• A.

0.75 A

• B.

Zero

• C.

0.25 A

• D.

0.5 A

D. 0.5 A
Explanation
In the given circuit, two ideal diodes are connected in parallel to a battery. An ideal diode allows current to flow in only one direction. When the battery is connected, one of the diodes will be forward biased and the other will be reverse biased. The forward biased diode will allow current to flow through it, while the reverse biased diode will block the current. Therefore, the current supplied by the battery will be determined by the forward biased diode, which is 0.5 A.

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• Current Version
• Sep 04, 2023
Quiz Edited by
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• Jan 30, 2014
Quiz Created by
Tanmay Shankar

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