The interest of the magnetic hysteresis graph is that it serves as an important characterization of a :This curve will also tell you how many turns of the coil will be needed to reach the required field.
- its area gives you the hysteresis loss of the transformer, which is a major cause of efficiency loss of the component
- some key points of the curve give important characterizations of the core/material:
- Saturation magnetisation
- magnetization strength without field
- how much field you need to demagnetize it
Theoretical magnetic hysteresis plot
. Source. 1989. 1989 and they were making such awesome materials. It is hard to understand why university still exists given this.
Shows how you can obtain the magnetic hysteresis curve with an AC source plus an oscilloscope in XY mode. youtu.be/pXukVix5Pcw?t=193 clearly shows the measurement circuit.
Magnetic hysteresis experiment by UNSW Physics.
Source. 2020, thanks COVID-19. Like other UNSW Physics YouTube channel videos, the experimental setup could be made clearer with diagrams.
But this video does have one merit: it shows that the hysteresis plot can be obtained directly with the oscilloscope XY mode by using an AC source. The Y axis is just a measure of the total magnetic field induced by the primary coil + the magnetization of the material itself.
The first application of mobile phones was in motor vehicles by 
Ciro Santilli 37 Updated 2025-06-17 +Created 2024-06-26
Ciro Santilli 37 Updated 2025-06-17 +Created 2024-06-26Early models were heavy and not practical for people to carry them, so the main niche they initially filled was being carried in motor vehicles, notably trucks where drivers are commercially driving all day long.
It also helps in the case of trucks that you only need to cover a one-dimensional region of the main roads.
Easy-to-Build Electromagnet lifts over 50 lbs by Dorian McIntire
. Source. Fun, but zero reproducibility.Solenoids are simpler to build as they don't require insulated wire as in modern electrical cable because as the electromagnetic coils don't touch one another.
As such it is perhaps the reason why some early electromagnetism experiments were carried out with solenoids, which André-Marie Ampère named in 1823.
But the downside of this is that the magnetic field they can generate is less strong.
Magnetic field lines around a solenoid cross-section
. TODO accurate simulation or not?Electromagnets allow us to create controllable magnetic fields, i.e.: they act as magnets that we can turn on and off as we please but controlling an input voltage.
Compare them to permanent magnet: on a magnet, you always have a fixed generated magnetic field. But with an electromagnet you can control the field, and even turn it off entirely.
This type of "useful looking thing that can be controlled by a voltage" tends to be of huge importance in electrical engineering, the transistor being another example.
electronics.stackexchange.com/questions/477264/spectrum-of-leds claims cheap LEDs have 20 nm width at 50% from peak, and cheap lasers can be 1 nm or much less
These were the earlier attempts at decision making systems that could replace intellectual jobs.
Their main problem is that it is very costly to acquire data, which is kind of the main issue that large language models address with their ability to consume natural language input.
www.reddit.com/r/Optics/comments/18f6bdt/comment/kcsiook/ mentions:
LEDs are broadband by nature, since the spontaneous emission broadly speaking reflects the overlap of the Fermi distribution and the density of states
Plaintext file of An English translation by Barbara Foxley from 1911 on Project Gutenberg: www.gutenberg.org/cache/epub/5427/pg5427.txt which is in the Public domain in the United States.
Can't find a French txt, fr.wikisource.org/wiki/Émile,_ou_De_l’éducation/Édition_1782 has a PDF though.
Good summary on the defunct Encyclopedia Britannica: www.britannica.com/topic/Emile-or-On-EducationAlso:
it is not specifically about schooling but about the upbringing of a rich man’s son, Émile, by a tutor who is given unlimited authority over him. Rousseau’s aim throughout Émile is to show how a natural education, unlike the artificial and formal education of society, enables Émile to become social, moral, and rational while remaining true to his original nature
Book 1:Source:
There are in several schools, and especially in the University of Paris, Professors whom I like, whom I esteem very much, and whom I believe very capable of instructing young people well, if they were not forced to follow established usage. I urge one of them to publish the reform project he designed. We will perhaps finally be tempted to cure the illness by seeing that it is not without a remedy.
Je n’envisage pas comme une institution publique ces risibles établissements qu’on appelle CollegesIl y a dans plusieurs écoles, & surtout dans l’Université de Paris, des Professeurs que j’aime, que j’estime beaucoup, & que je crois très capables de bien instruire la jeunesse, s’ils n’étoient forcés de suivre l’usage établi. J’exhorte l’un d’entre eux à publier le projet de réforme qu’il a conçu. L’on sera peut-être enfin tenté de guérir le mal en voyant qu’il n’est pas sans remède.
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