Fundamentals of Electronics Semester III
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Questions and Answers

What characterizes an insulator's energy band structure?

  • High conductivity comparable to conductors
  • Full conduction band with free electrons
  • A very small forbidden band gap
  • A large forbidden band gap greater than 5 eV (correct)

    • Which of the following materials is classified as an insulator?

  • Aluminum
  • Copper
  • Glass (correct)
  • Gold

    • What is the typical resistivity level of an insulator?

  • 10^6 to 10^8 Ω-cm
  • 10^10 to 10^12 Ω-cm (correct)
  • 10^2 to 10^4 Ω-cm
  • 10^1 to 10^3 Ω-cm

    • What does the term 'forbidden band gap' indicate in semiconductors?

    <p>It is the energy required for a valence electron to become free</p> Signup and view all the answers

    Which statement is true regarding conductors?

    <p>Conductors support a generous flow of charge when voltage is applied</p> Signup and view all the answers

    Which of the following is a defining property of semiconductors?

    <p>Good conductivity only in certain conditions</p> Signup and view all the answers

    What happens to an insulator's conductivity with an increase in temperature?

    <p>It remains virtually unchanged</p> Signup and view all the answers

    Which element is not a typical example of a conductor?

    <p>Mica</p> Signup and view all the answers

    What type of semiconductor is formed by adding trivalent atoms?

    <p>P-type semiconductor</p> Signup and view all the answers

    In an N-type semiconductor, what is primarily responsible for the increase in conductivity?

    <p>The presence of excess electrons from donor atoms</p> Signup and view all the answers

    What is the relationship between majority and minority carriers in P-type semiconductors?

    <p>Holes are majority carriers while electrons are minority carriers</p> Signup and view all the answers

    What is the primary reason for the decrease in holes in N-type semiconductors?

    <p>The recombination of electrons with holes</p> Signup and view all the answers

    Which of the following impurities is NOT typically used to create an N-type semiconductor?

    <p>Boron</p> Signup and view all the answers

    What energy difference corresponds to freeing the fifth valence electron for silicon?

    <p>0.05 eV</p> Signup and view all the answers

    Which statement is true regarding the conduction band and donor energy levels in semiconductors?

    <p>The difference provides the energy needed to free electrons</p> Signup and view all the answers

    Which of the following statements about electron mobility in N-type semiconductors is accurate?

    <p>Electrons have greater mobility than holes</p> Signup and view all the answers

    What happens to the diode during the negative cycle of the input in the negative cycle of the input?

    <p>The diode becomes forward biased.</p> Signup and view all the answers

    What is characteristic of the voltage output across the load resistor during the negative cycle of the input?

    <p>It is equal to the applied input voltage.</p> Signup and view all the answers

    In the Positive Series Clipper with positive Vr, what occurs during the positive cycle of the input?

    <p>The diode gets reverse biased and the reference voltage appears at the output.</p> Signup and view all the answers

    What is the primary function of a Positive Series Clipper with negative Vr?

    <p>It attenuates the positive portions of the waveform.</p> Signup and view all the answers

    What causes the difference between the ideal output and the practical output waveforms?

    <p>The diode conduction voltage.</p> Signup and view all the answers

    What will the output signal look like if the input is greater than the negative reference voltage during the negative cycle?

    <p>It will appear as the full input waveform.</p> Signup and view all the answers

    What happens to the voltage across V0 in relation to the output load voltage in practical applications?

    <p>It is affected by the diode conduction voltage.</p> Signup and view all the answers

    What is the purpose of the current limiting resistor in an LED circuit?

    <p>To protect the LED from excessive current</p> Signup and view all the answers

    What happens to the LED when the output of the digital circuit is in a high state?

    <p>The LED receives no voltage and remains off</p> Signup and view all the answers

    During which cycle does the diode in a Positive Series Clipper with negative Vr conduct like a closed switch?

    <p>Only during the negative cycle.</p> Signup and view all the answers

    What is the primary function of the error amplifier in a SMPS?

    <p>To determine the switching frequency</p> Signup and view all the answers

    Which of the following is a key disadvantage of SMPS?

    <p>Electromagnetic interference</p> Signup and view all the answers

    Which layer is NOT mentioned as part of the basic LCD structure?

    <p>Electromagnetic field</p> Signup and view all the answers

    What is the role of the polarizing filters in an LCD?

    <p>They block light entirely without liquid crystals</p> Signup and view all the answers

    What is one main type of SMPS used for obtaining regulated DC output?

    <p>AC to DC Converter</p> Signup and view all the answers

    Which statement correctly describes the operational mode of the switching device in SMPS?

    <p>It operates in saturation or cut off mode.</p> Signup and view all the answers

    What effect does adjusting the voltage on the electrodes in an LCD have?

    <p>It varies the twist of the liquid crystal</p> Signup and view all the answers

    What is a primary application of SMPS?

    <p>Motor vehicles</p> Signup and view all the answers

    Why is the alignment layer important in an LCD structure?

    <p>It facilitates proper orientation of liquid crystal molecules</p> Signup and view all the answers

    Which component allows displays to be used in ambient light conditions?

    <p>Reflector</p> Signup and view all the answers

    Which type of converter in SMPS is primarily used for low power applications?

    <p>Fly back Converter</p> Signup and view all the answers

    What range does the efficiency of SMPS typically fall within?

    <p>80 to 90%</p> Signup and view all the answers

    In an LED circuit, what does a low output in a digital circuit indicate?

    <p>The LED is forward biased and will light up</p> Signup and view all the answers

    Which of the following factors contributes to the high efficiency of SMPS?

    <p>Switching the input to control the output</p> Signup and view all the answers

    Study Notes

    Semiconductor Devices Overview

    • Materials categorized as insulators, semiconductors, and conductors based on electrical conductivity.
    • Insulators: Very low conductivity; resistivity ranges from 10^10 to 10^12 Ω-cm. Example materials include paper, mica, glass, and quartz.
    • Energy Bands:
      • Valence band: Electrons are bound to atoms, do not conduct electricity.
      • Conduction band: Electrons free to move, allowing current flow.
      • Forbidden band gap: Energy needed for an electron to transition from valence to conduction band; large gap (>5 eV) in insulators results in poor conductivity.

    Conductors and Semiconductors

    • Conductors: High conductivity materials like copper, aluminum, silver, and gold. Rarely have a band gap, allowing excellent conductivity.
    • N-Type Semiconductors: Created by doping with pentavalent impurities (e.g., phosphorus). Increased conduction electrons dominate current flow; holes become minority carriers due to electron recombination.
    • P-Type Semiconductors: Formed by doping with trivalent impurities (e.g., boron). Introduces holes as majority carriers and reduces electron concentration; these impurities are termed acceptors.

    Circuit Behavior

    • Diode Functionality:
      • Forward bias: diode conducts, acts as a closed switch.
      • Reverse bias: diode does not conduct; output voltage reflects the input.
    • Positive Series Clipper: Either positive or negative reference voltage alters signal peaks based on diode biasing.

    Switched Mode Power Supply (SMPS)

    • Operates by switching to regulate voltage, achieving high efficiency (80-90%).
    • Advantages: Compact design, reduced heat generation, minimized harmonic feedback.
    • Disadvantages: Complexity, electromagnetic interference, and noise from high-frequency switching.
    • Common applications: Computer motherboards, chargers, power distribution, motor vehicles, and consumer electronics.
    • Types include DC to DC Converter, AC to DC Converter, Flyback Converter, and Forward Converter.

    Liquid Crystal Display (LCD) Basics

    • Composed of polarizing filters, transparent electrodes, liquid crystal material, and reflector/light source.
    • Light modulation occurs by adjusting voltages which control the twist of liquid crystals, allowing variable light passage.
    • Key components include layers of indium-tin-oxide (ITO), glass, alignment layers, and polarizers, potentially arranged to optimize performance.
    • Reflective surfaces enable usage in ambient light conditions, enhancing visibility and functionality.

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    Fundamental Of Electronics (Unit 1) PDF

    Description

    This quiz covers the basics of semiconductor devices, focusing on their electrical conductivity and classification. Learn about insulators, semiconductors, and conductors as you test your understanding of this essential topic in computer engineering.

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