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Subel. E6
12 questions
Subelement E6

CIRCUIT COMPONENTS

Section E6D

Inductors and piezoelectricity: permeability, core material and configuration; transformers; piezoelectric devices

What is piezoelectricity?

  • The ability of materials to generate electromagnetic waves of a certain frequency when voltage is applied
  • A characteristic of materials that have an index of refraction which depends on the polarization of the electromagnetic wave passing through it
  • Correct Answer
    A characteristic of materials that generate a voltage when stressed and that flex when a voltage is applied
  • The ability of materials to generate voltage when an electromagnetic wave of a certain frequency is applied
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What is the equivalent circuit of a quartz crystal?

  • Correct Answer
    Series RLC in parallel with a shunt C representing electrode and stray capacitance
  • Parallel RLC, where C is the parallel combination of resonance capacitance of the crystal and electrode and stray capacitance
  • Series RLC, where C is the parallel combination of resonance capacitance of the crystal and electrode and stray capacitance
  • Parallel RLC, where C is the series combination of resonance capacitance of the crystal and electrode and stray capacitance

Remember:

series RLC + shunt capacitance.

The only answer that includes the mention of a shunt capacitor is the correct choice.

Last edited by w7fzy. Register to edit

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Which of the following is an aspect of the piezoelectric effect?

  • Correct Answer
    Mechanical deformation of material due to the application of a voltage
  • Mechanical deformation of material due to the application of a magnetic field
  • Generation of electrical energy in the presence of light
  • Increased conductivity in the presence of light

Ever used piezo ignition for your gas stove or oven? https://en.wikipedia.org/wiki/Piezo_ignition

This is using the same property: you press a button (usually hard!) to deform a crystal and as a result you get a nice little spark due to a (brief) high voltage.

So if you deform the crystal, you get a voltage. You can also apply a voltage to deform the crystal.

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Why are cores of inductors and transformers sometimes constructed of thin layers?

  • To simplify assembly during manufacturing
  • Correct Answer
    To reduce power loss from eddy currents in the core
  • To increase the cutoff frequency by reducing capacitance
  • To save cost by reducing the amount of magnetic material
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How do ferrite and powdered iron compare for use in an inductor core?

  • Ferrite cores generally have lower initial permeability
  • Ferrite cores generally have better temperature stability
  • Correct Answer
    Ferrite cores generally require fewer turns to produce a given inductance value
  • Ferrite cores are easier to use with surface-mount technology

Because ferrite toroids have a higher permeability than powdered-iron toroids, the inductance for a given number of turns is increased. Therefore, smaller inductors and inductors with fewer turns are possible using ferrite toroids.

Memory tip:
Ferrite Toroids = Fewer Turns

Hint: 'Inductor' is in the question and 'Inductance' only appears in the correct answer.

Last edited by kd7bbc. Register to edit

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What core material property determines the inductance of an inductor?

  • Permittivity
  • Resistance
  • Reactivity
  • Correct Answer
    Permeability

Permeability is a measure of the response of a given material to a magnetic field. The measure is relative to the magnetic field strength observed with no core. A higher permeability will result in a higher inductance for a constant number of turns on the toroid. It is measured in henries per meter. Air has a permeability of 1. So, the permeability of the material used in the core of the toroid will have the biggest impact on its inductance

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What is the current that flows in the primary winding of a transformer when there is no load on the secondary winding?

  • Stabilizing current
  • Direct current
  • Excitation current
  • Correct Answer
    Magnetizing current

Even if there is no load, a small amount of current flows through a transformer when AC is applied. This current creates a magnetic field, and is called the magnetizing current.

If there is a load on the secondary, it acts to deplete the magnetic field and generally increases the amount of current flowing in the primary beyond the magnetizing current.

Last edited by icee. Register to edit

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Which of the following materials has the highest temperature stability of its magnetic characteristics?

  • Brass
  • Correct Answer
    Powdered iron
  • Ferrite
  • Aluminum
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What devices are commonly used as VHF and UHF parasitic suppressors at the input and output terminals of a transistor HF amplifier?

  • Electrolytic capacitors
  • Butterworth filters
  • Correct Answer
    Ferrite beads
  • Steel-core toroids

The ferrite bead (small sphere of ferrite with a hole through it) is a very small core and acts as a filter to suppress higher frequency noise.

https://en.wikipedia.org/wiki/Ferrite_bead

Last edited by chevdor. Register to edit

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What is a primary advantage of using a toroidal core instead of a solenoidal core in an inductor?

  • Correct Answer
    Toroidal cores confine most of the magnetic field within the core material
  • Toroidal cores make it easier to couple the magnetic energy into other components
  • Toroidal cores exhibit greater hysteresis
  • Toroidal cores have lower Q characteristics

Because of the circular geometry of the toroidal core, it contains most of the magnetic field inside the core. This makes toroids well suited for use on circuit boards where magnetic field interference with other components is undesirable.

Hint: All answers start with "Toroidal cores". What is important is that the the correct answers' 3rd word comes first alphabetically among all the answers. The "C" in confines is the first alphabetically.

Another hint: the question has the word "core" twice and so does the answer.

Last edited by tycen. Register to edit

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Which type of core material decreases inductance when inserted into a coil?

  • Ceramic
  • Correct Answer
    Brass
  • Ferrite
  • Aluminum

Ferrite is found in many electromagnetic applications because it increases inductance, allowing smaller, lighter parts to do the same job. Powdered iron fits a similar role, also increasing inductance. Brass is pretty much only used in variable inductors because it reduces inductance compared to the air it displaces as you turn the slug. Normally you'd just make a smaller coil, but sometimes other constraints exist. Ceramic is inert and doesn't do anything.

Hint: Slug think bullet and brass is the common casing.

Last edited by michaelv. Register to edit

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What causes inductor saturation?

  • Operation at too high a frequency
  • Selecting a core with low permeability
  • Correct Answer
    Operation at excessive magnetic flux
  • Selecting a core with excessive permittivity
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