This is an old revision of the document!
Table of Contents
Conceptual Electronics Videos
I just found a series of videos that animate various physics concepts. The first one I found was on the concept of impedance:
But this was #15 in a series of 24 videos. I just finished watching the first few and they basically managed to start from scratch and work their way up to Electro-Magnetism pretty much without math. One thing they could have improved though is the labelling. So while you watch these, keep in mind that:
- Red particles are positive charges
- Blue particles are negative charges
- Purple arrows are electric fields
- Green arrows are magnetic fields.
Here's the first video:
This first video can seem pretty overwhelming, with all these fields creating each other, but there's really only four rules that govern it all:
Name | Math | Description |
---|---|---|
Gauss' Law | $$\vec{\nabla} \cdot \vec{E} = \frac{\rho}{\varepsilon_0}$$ | An electric charge (right) creates an electric field that points away from the charge and “disperses” to infinity (left) |
Gauss' Law of Magnetism | $$\vec{\nabla} \cdot \vec{B} = 0$$ | A magnetic field (left) can not “disperse” to infinity the way an electric field can. In other words: “magnetic charges” don't exist the way electric charges do. |
Faraday's Law of Induction | $$\vec{\nabla} \times \vec{E} = -\frac{\partial \vec{B}}{\partial t}$$ | A changing magnetic field (right) creates a “curly” electric field (left) and vice-versa. |
Ampere's Law | $$\vec{\nabla} \times \vec{B} = \mu_0 \Big(\vec{J} + \varepsilon_0 \frac{\partial \vec{E}}{\partial t} \Big)$$ | An electric current and/or a changing electric field (right) creates a “curly” magnetic field (left) |
Together, these four equations (known as Maxwell's Equations) account for all the electromagnetic phenomena we observe:
- [4:00] Magnetic fields exerts a force on moving charged particles because a moving charged particle creates curly magnetic field around it (Ampere's Law) so the particle behaves like a magnet. This is the principle behind old Cathode Ray Tube TVs: send electrons flying toward a screen that can image them, and adjust their deflection using a magnetic field.
- [4:16] A charged particle moving in a loop creates a magnetic field (Ampere's Law) which is the same for a spinning electric charge, which is the what permanent magnets are made of. Notice how the magnetic field lines form closed loops (Gauss' Law of Magnetism).
- [5:20] Magnetic fields can be created by a current through a wire (Ampere's Law)