Spectophotometry Updated +Created
Video 1.
Donated Eskalab Spectrophotometer by CuriousMarc
. Source.
Single-mode and multi-mode optical fiber Updated +Created
From a practical point of view single-mode:
  • upside: can go further without a repeater. In multi-mode optical fiber, different modes travel at different speeds, and start interfering with each other at some point
  • downside: lower bandwitdh, because we can fit less modes into it
As such, typical applications are:
From a mathematical point of view:
Saturation magnetisation Updated +Created
Light source characteristic Updated +Created
Ethernet over fiber Updated +Created
Ethernet over twisted pair Updated +Created
Magnetic hysteresis Updated +Created
To understand the graph, first learn/remember the difference between the magnetic B and H field.
The interest of the magnetic hysteresis graph is that it serves as an important characterization of a :
  • 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:
This curve will also tell you how many turns of the coil will be needed to reach the required field.
Figure 1.
Theoretical magnetic hysteresis plot
. Source.
Video 1.
Measurement of B-H characteristic
. 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.
Video 2.
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.
Ice Ih Updated +Created
The first application of mobile phones was in motor vehicles Updated +Created
Early 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.
For example, this niche was the original entry point of companies such as:
History of mobile phone Updated +Created
Ethernet physical layer Updated +Created
Lifting electromagnet Updated +Created
Video 1.
Easy-to-Build Electromagnet lifts over 50 lbs by Dorian McIntire
. Source. Fun, but zero reproducibility.
Solenoid Updated +Created
Solenoids are a type of electromagnet coil of helical shape.
Solenoid means "tubular" in Greek.
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.
Figure 1.
Illustration of a solenoid
.
Figure 2.
Magnetic field lines around a solenoid cross-section
. TODO accurate simulation or not?
Picturephone Updated +Created
ethw.org/Picturephone good article!
Video 1.
AT&T Picturephone Model 2
. 1969
Public domain in the United States Updated +Created
Oscilloscope XY mode Updated +Created
Electromagnet Updated +Created
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.
Laser spectrum vs LED spectrum Updated +Created
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

There are unlisted articles, also show them or only show them.