From Wikipedia:

Piezoelectricity is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress.

The piezoelectric effect is a reversible process: materials exhibiting the piezoelectric effect also exhibit the reverse piezoelectric effect, the internal generation of a mechanical strain resulting from an applied electric field.

Last edited by samdypaulson. Register to edit

Tags: none

Remember:

series RLC + shunt capacitance.

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

Last edited by kf8bfm. Register to edit

Tags: arrl chapter 6 arrl module 6d

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.

Last edited by chevdor. Register to edit

Tags: arrl chapter 6 arrl module 6d

When a changing magnetic field interacts with a solid conductor, it induces circulating currents within the conductor. These currents are called eddy currents and they dissipate energy as heat. By using thin layers of magnetic material instead of a solid core, the path for eddy currents is significantly reduced. This is because the current tends to flow in loops, and the thin layers act like many smaller conductors, disrupting these loops and hindering the flow of eddy currents. By minimizing eddy currents, the core experiences less heat generation and overall power loss is reduced. This is crucial for efficient operation of inductors and transformers.

Last edited by senfo. Register to edit

Tags: none

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

Tags: arrl chapter 4 arrl module 4e

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

Last edited by k0llo. Register to edit

Tags: arrl chapter 4 arrl module 4e

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

Tags: arrl chapter 4 arrl module 4e

High temperature iron powder, as the name suggests, is a specialty powder able to withstand elevated temperatures without degrading. While ordinary iron powders may begin to oxidize or lose their magnetic abilities above 300-400°C, high temp powders resist these changes even beyond 1000°C.

Source: https://am-material.com/news/high-temperature-iron-powder/

Last edited by thesonicgod. Register to edit

Tags: none

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

Tags: arrl chapter 4 arrl module 4e

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

Tags: arrl chapter 4 arrl module 4e

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

Tags: arrl chapter 4 arrl module 4e

Saturation of a magnetic material occurs when the metal has absorbed as much of the magnetic field as it can. Thus, an inductor goes into saturation when there is too much magnetic flux for it to absorb.

The permeability of a material does not itself cause saturation, but only changes how much flux is required before it saturates. If you know your magnetic field will never get that strong, then you can safely use a core with a lower permeability.

Saturation is less common at higher frequencies, as the inductor has less time to absorb the magnetic field before the signal reverses. Permittivity is relevant to capacitors and electric fields and has no relevance here.

https://en.wikipedia.org/wiki/Saturation_(magnetic)

Last edited by ky1ff. Register to edit

Tags: none