#Magnetic cores
frosty vortex
It depends on what you learn best from. There are some good books and videos. This one is old, but gives a good foundation (and physics hasn't changed over the years): https://vimeo.com/292244109
If you prefer books, a really good one is "Learning the Art of Electronics: The X Chapters", which has excellent coverage of magnetics. Würth Elektronik also publishes a nice book called "The Trilogy of Magnetics"
This site is generally helpful as well: https://www.electronics-tutorials.ws/inductor/inductor.html
eager summit