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Subel. ZLB
20 questions
Subelement ZLB

Basic Electrical Theory

Section ZLB11

Semiconductors

The basic semiconductor amplifying device is a

  • diode
  • Correct Answer
    transistor
  • pn-junction
  • silicon gate
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Zener diodes are normally used as

  • RF detectors
  • AF detectors
  • current regulators
  • Correct Answer
    voltage regulators
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The voltage drop across a germanium signal diode when conducting is about

  • Correct Answer
    0.3V
  • 0.6V
  • 0.7V
  • 1.3V
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A bipolar transistor has three terminals named

  • base, emitter and drain
  • collector, base and source
  • Correct Answer
    emitter, base and collector
  • drain, source and gate
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The three leads from a PNP transistor are named the

  • collector, source, drain
  • gate, source, drain
  • drain, base, source
  • Correct Answer
    collector, emitter, base
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A low-level signal is applied to a transistor circuit input and a higher-level signal is present at the output. This effect is known as

  • Correct Answer
    amplification
  • detection
  • modulation
  • rectification
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The type of rectifier diode in almost exclusive use in power supplies is

  • lithium
  • germanium
  • Correct Answer
    silicon
  • copper-oxide

Correct answer: silicon

Modern power supply rectifiers almost exclusively use silicon diodes. Silicon devices offer:

  • low cost and wide availability
  • high reverse voltage ratings
  • good current handling capability
  • excellent reliability and long life
  • stable operation over a wide temperature range

These characteristics make silicon ideal for mains rectification and general power supply use.

  • lithium is not used as a rectifier material in practical power electronics.
  • germanium diodes were used in early electronics but have lower voltage ratings, higher leakage current, and poorer temperature stability than silicon.
  • copper-oxide rectifiers are obsolete and inefficient compared with modern semiconductor diodes.

Therefore, the rectifier diode almost exclusively used in power supplies is silicon.

Last edited by jim.carroll. Register to edit

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One important application for diodes is recovering information from transmitted signals. This is referred to as

  • biasing
  • rejuvenation
  • ionisation
  • Correct Answer
    demodulation
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In a forward biased pn junction, the electrons

  • flow from p to n
  • Correct Answer
    flow from n to p
  • remain in the n region
  • remain in the p region
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The following material is considered to be a semiconductor

  • copper
  • sulphur
  • Correct Answer
    silicon
  • tantalum
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A varactor diode acts like a variable

  • resistor
  • voltage regulator
  • Correct Answer
    capacitor
  • inductor

Correct answer: capacitor

A varactor diode is designed to operate in reverse bias, where the width of its depletion region changes with applied voltage. This change in depletion width causes the diode’s junction capacitance to vary as the reverse voltage changes.

As the reverse voltage increases, the depletion region widens and the capacitance decreases. As the reverse voltage decreases, the capacitance increases. This makes the device behave like a voltage-controlled variable capacitor.

  • resistor is incorrect because the diode is reverse biased and ideally conducts very little current.
  • voltage regulator is incorrect because the device does not regulate voltage, it varies capacitance.
  • inductor is incorrect because no magnetic field or inductive behaviour is involved.

Therefore, a varactor diode acts like a variable capacitor.

Last edited by jim.carroll. Register to edit

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A semiconductor is said to be doped when small quantities of the following are added

  • electrons
  • protons
  • ions
  • Correct Answer
    impurities
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The connections to a semiconductor diode are known as

  • cathode and drain
  • Correct Answer
    anode and cathode
  • gate and source
  • collector and base
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Bipolar transistors usually have

  • 4 connecting leads
  • Correct Answer
    3 connecting leads
  • 2 connecting leads
  • 1 connecting lead
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A semiconductor is described as a "general purpose audio NPN device". This is a

  • triode
  • silicon diode
  • Correct Answer
    bipolar transistor
  • field effect transistor
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Two basic types of bipolar transistors are

  • p-channel and n-channel types
  • Correct Answer
    NPN and PNP types
  • diode and triode types
  • varicap and zener types
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A transistor can be destroyed in a circuit by

  • excessive light
  • Correct Answer
    excessive heat
  • saturation
  • cut-off
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To bias a transistor to cut-off, the base must be

  • at the collector potential
  • Correct Answer
    at the emitter potential
  • mid-way between collector and emitter potentials
  • mid-way between the collector and the supply potentials
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Two basic types of field effect transistors are

  • Correct Answer
    n-channel and p-channel
  • NPN and PNP
  • germanium and silicon
  • inductive and capacitive
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A semiconductor with leads labelled gate, drain and source, is best described as a

  • bipolar transistor
  • silicon diode
  • gated transistor
  • Correct Answer
    field-effect transistor
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