Semiconductors MCQ Quiz - Objective Question with Answer for Semiconductors - Download Free PDF

Calculation:

The diode with reverse bias acts as an open circuit due to its infinite backward resistance, so no current flows through that branch.

The current flows only through the branch containing the forward-biased diode and the 100 ohm resistor.

Effective resistance of the path is: 50 Ω (diode) + 150 Ω + 100 Ω = 300 Ω

Using Ohm's law: I = V / R = 6 / 300 = 0.02 A

Answer: Option (B)

​Calculation:

Given inputs: A = 1, B = 1

Top AND gate

Input: 1, 1 ⇒ Output = 1

NOT gates

NOT(1) = 0 for both A and B

OR gate before P

Inputs to final OR gate (for P): 1 (from AND gate), 0 (from NOT) ⇒ Output = 1 OR 0 = 1

Then passed through final AND with another input 0 ⇒ 1 AND 0 = 0

⇒ P = 0

For Q

Inputs to OR gate before Q: 0 (NOT A), 0 (NOT B) ⇒ Output = 0

AND gate with inputs 0 and 0 ⇒ 0

⇒ Q = 0

Final Answer: P = 0, Q = 0

Hence, the correct option is (2).

Explanation:

Statement – I is correct.

When a P-N junction is formed, an electric field is generated from the N-side to the P-side. This electric field creates a barrier potential at the junction. Due to this barrier potential, the majority charge carriers (electrons in the N-side and holes in the P-side) cannot flow through the junction on their own. As a result, the current is zero unless a forward bias voltage is applied to the junction, which allows the charge carriers to overcome the barrier potential and flow across the junction.

Explanation:

Photodiodes are operated in reverse bias condition.

For a P-N junction, current in forward bias (for V ≥ V₀) is always greater than current in reverse bias (for V ≤ V_Z).

Hence Assertion is false but Reason is true.

Correct option is: (2) D₁ is reverse biased, D₂ is forward biased

V_in = 220 × sin(100πt) volt

Given: t = 15 ms = 0.015 s

ω = 100π

2π / T = 100π

⇒ T = 1 / 50 s

⇒ T = 0.02 s

Now, t = (3T / 4)

i.e., the signal is in the negative half cycle.

So now the negative half cycle is fed to the circuit, making D₁ reverse biased and D₂ forward biased.

CONCEPT:

• Logic gate: The digital circuit that can be analysed with the help of Boolean algebra is called a logic gate or logic circuit.
• A logic gate has two or more inputs but only one output.

EXPLANATION:

• NOR gate: It is a digital circuit having two or more inputs but only one output.
• It gives a high output if either input A or B or both are low (0) otherwise it gives a high output (1).
• It is described by the Boolean expression: \(\overline {A + B} = Q\)
• The above logic gate is the NOR gate.

Truth table for NOR gate:

CONCEPT:

• Semiconductors: The materials that have a conductivity between conductors and insulators are called semiconductors.
  • Even though carbon lies in the same group of the periodic table as germanium and silicon, it is not a pure or an intrinsic semiconductor.

EXPLANATION:

• When the external voltage becomes greater than the value of the potential barrier for the diode the potential barriers opposition will be overcome and the current will start to flow. This is the conventional current.
• The potential barrier is approx 0.3 volts for germanium and 0.7 volts for silicon while for the carbon it is 7eV.
• This is far much higher for Carbon to make it a semiconductor that has lower forbidden energy gaps (Si and Ge).
• This is why Carbon is not a semiconductor.
• So the correct answer is option 1.

​Additional Information

The correct answer is option 2 i.e. Silver.

Concept:

Alloy:

• A metal made by combining two or more metals to obtain few desirable qualities such as more strength, resistance to corrosion.
• Some Properties of metals for which they are widely used are because they have-
• High melting points.
• Good conductors of electricity.
• Good conductors of heat.
• High density.
• Malleability.
• Ductility

Explanation:

Few examples of alloys, their composition, and their uses are as follows:

• Solder, brass, and bronze are alloys but silver is pure metal.

Hence, silver is NOT an alloy.

Additional Information

Amalgam

• Amalgam is an alloy of mercury and one or more other metals likes silver, tin, copper and zinc etc.
• Amalgams are crystalline in structure, except mercury which is liquid.
• An amalgam of silver and tin, with minor amounts of copper and zinc, is used to fill teeth.
• A sodium amalgam is formed during the manufacture of chlorine and sodium hydroxide by the electrolysis of brine in cells wherein a stream of mercury constitutes the negative electrode.
• The reaction of the amalgam with water produces a solution of sodium hydroxide and regenerates the mercury for reuse.

• Valance electrons are responsible for electrical conductivity of an element
• The outermost shell for a given atom is called the valence shell
• The valence shell of an atom can contain up to eight electrons
• The conductivity of the atom depends on the number of electrons that are in the valence shell

Important:

Based on electrical conductivity, the elements are divided into three groups:

Conductors:

All metallic substances are a good conductor of electricity. it has less than 4 electrons in its outermost shell that means it has less than four valence electrons.

Semiconductors:

Semiconductors are materials that have a conductivity between conductors (generally metals) and non-conductors or insulators. It has 4 valance electrons in the outermost shell.

Insulators:

CONCEPT:

• When a p-type semiconductor crystal is brought into close contact with an n-type semiconductor crystal, the resulting arrangement is called p-n junction diode.

EXPLANATION:

Forward Bias:

• When the negative terminal of the battery is connected to the N – side and the positive terminal to P –side, then the connection is called forward bias.
• In forward biasing, the applied voltage V of the battery mostly drops across the depletion region and the voltage drops across the p-side and n-side of the p-n junction is negligibly small.
• It is because the resistance of the depletion region is very high as it has no free charge carriers.
• A p - n junction diode allows electric current in one direction and blocks electric current in another direction.
• It allows electric current when it is forward biased and blocks electric current when it is reverse biased.
• An actual diode offers a very small resistance (ideally zero but actually very low) when forward biased and is called forward resistance. Therefore option 3 is correct.

• In forward biasing the forward voltage opposes the potential barrier Vb. As a result of it, the potential barrier height is reduced and the width of the depletion layer decreases.
• As forward voltage is increased, at a particular value the depletion region becomes very much narrow such that a large number of majority charge carriers can cross the junction.

• On the basis of the relative values of electrical conductivity (s) or resistivity, the solids are broadly classified as:

1. Metals: They possess very high conductivity or low resistivity.
2. Semiconductors: They have conductivity or resistivity intermediate to metals and insulators.
3. Insulators: They have high resistivity (or low conductivity).

EXPLANATION:

• Semiconductors have resistivity between metals and insulators.
• By doping an intrinsic semiconductor, we can modulate its electrical properties.
• So the correct answer is option 1.

CONCEPT:

Logic Gates:

• The logic gates are used in electronic circuits that give a certain output for a given set of Inputs.
• and which is based on a certain logic. 
• Input and output are in binary form that is 1 and 0.
• It is based on certain Logic.
• Some basic logic gates are AND gate, OR gate, NOT gate. 
• To build digital logic we develop a combination of these gates. 

AND Gate:

•  If both the inputs are high, it produces a high output.
• The Boolean algebra for AND gate is X = A. B
• It means that if any of the input of A and B is zero, the output will be zero.
• If both are one, the output will be one.

NOT gate: 

• It inverts the input. Whatever the input is given, it changes its value at the output.
• The Boolean algebra for NOT gate is X = X̅

EXPLANATION:

NAND Gate:

• The NAND Gate is formed by the combination of AND gate and NOT gate. 
• The output obtained from AND Gate is simply reversed. 

• The output of the NAND Gate is similar to the output in the question.

So, the correct option is NAND Gate.

Additional Information

OR gate: 

• If any of the input is high, it produces a high output.
• The Boolean algebra for OR gate is X = A + B

CONCEPT:

Forward Bias: 

• When the negative terminal of the battery is connected to the N - side and the positive terminal to P - side the connection is called forward bias.

EXPLANATION:

• In forward biasing, the applied voltage V of the battery mostly drops across the depletion region and the voltage drops across the p-side and n-side of the p-n junction is negligibly small.
• It is due to the fact that the resistance of the depletion region is very high as it has no free charge carriers.
• Due to concentration difference, holes try to diffuse from p-side to the n-side.
• But the electric field at the junction exerts a force on the holes towards left as they come to the depletion larger. Only those holes which start moving towards the right with a high kinetic energy are able to cross the junction.
• Similarly diffusion of electrons takes place from right to left. This diffusion results in an electric current from the p-side to the n-side known as diffusion current. Therefore option 3 is correct.

Additional Information

• In forward biasing the forward voltage opposes the potential barrier Vb. As a result of it, the potential barrier height is reduced and the width of the depletion layer decreases. 
• As forward voltage is increased, at a particular value the depletion region becomes very much narrow such that a large number of majority charge carriers can cross the junction.

CONCEPT:

• The material which is not a good conductor or a good insulator is called as a semiconductor. For example: Silicon, Germanium, etc.
• The semiconductor device which is used to control the flow of electric current is called a p-n junction diode.

• The depletion region/layer is an area at the junction where a field is formed because of the formation of a negative charge layer on the p side and a positive charge layer on the n side

EXPLANATION:

• The holes and electrons formed because of doping or impurities, diffuse to the other side respectively.
• So when a hole diffuses across the junction, it leaves a negative donor ion and the electron leaves a positive charge on the n side.
• These oppositely charged layers form a field due to the potential difference between the points which form the depletion region.
• All of the stated points contribute to the formation of the depletion region at the junction. So option 4 is correct.

The correct answer is option 1, i.e. LED.

• LED is the best source of light that consumes the least amount of energy.
  • LED is Light Emitting Diode which emits light when current flows through it.
  • It releases energy in the form of photons.
• The filament in an incandescent filament lamp is made of tungsten.

• The compact fluorescent lamp is a low-pressure mercury-vapour gas-discharge lamp that uses fluorescence to produce visible light.

  • It produces short-wave ultraviolet light.