What Is Electricity? (2013)

https://learn.sparkfun.com/tutorials/what-is-electricity/

by calinf • 7 years ago

126 45 7 years ago

learn.sparkfun.com

dang• 7 years ago

A thread from 2015: https://news.ycombinator.com/item?id=10400123

javajosh3• 7 years ago

One aspect of electricity I think is useful to emphasize is that electrons in a conductor move more like the steel balls Newton's cradle (that toy you may have seen where a ball strikes one end of a line of balls, and nothing moves except the end ball, or you can pull back two balls and then only two balls will move, and so on). This can help with intuition about the distinction between "holes" and electrons, and how energy can flow with holes (which is quite counter-intuitive, I think). In terms of mental model, the ratio of holes to ambient electrons is sometimes useful to think about, as this is fundamental to computing current limits of conductors.

There is a diagram (an animated GIF) about half-way down that sort of implies the newton's cradle method of moving charge, but I don't like it because it's not clear enough. Also, I see current as more of a fixed cloud of valence electrons with holes moving through it - which is a very different intuition than what this diagram implies.

Koshkin3• 7 years ago

Looks like what you are describing is a model of the conductivity in the valence band (of a semiconductor). In the conduction band of a metal electrons move freely, their forward mobility being impeded only by heat.

javajosh3• 7 years ago

Well, maybe the part about the holes. But even wikipedia mentions newton's cradle! https://en.wikipedia.org/wiki/Electrical_resistivity_and_con...

nixpulvis• 7 years ago

The distinction is between the speed of propagation (e.g. how fast between a light switch flipping until lighting the room) and the physical movement of subatomic particles through the wire.

https://en.m.wikipedia.org/wiki/Drift_velocity

lilgreenland9• 7 years ago

Here's my take on a cartoony conductivity simulation. I've got three models: conductors, semiconductors, and semiconductors but with holes.

https://landgreen.github.io/physics/notes/electromagnetism/c...

dreamcompiler2• 7 years ago

I like these diagrams. Now I want to see what superconductivity looks like in your framework. An unimpeded stream of electrons flowing as if the red dots aren't even there?

javajosh3• 7 years ago

Yes, that looks much closer to what I have in mind, although I also tend to think of electrons as not visible individually and doing this as part of a large cloud over a 3-D crystalline substrate.

lilgreenland9• 7 years ago

I teach high school physics. Here's my notes/textbook on electricity with simulations and equations rendered in LaTex.

https://landgreen.github.io/physics/notes/circuits/electrici...

new4thaccount• 7 years ago

I haven't gone through all of your notes yet, but this would've been a godsend to go over in highschool before I started my EE classes in college. It was always obvious which students had been lucky enough to already cover the material.

jaequery• 7 years ago

This is amazing ! Really well put together!

montecarl• 7 years ago

Awesome notes. I haven't had my coffee yet so perhaps I'm just misreading this part:

"In 1746 Benjamin Franklin mistakenly assigned a negative value to the charge carriers that we now call electrons."

Shouldn't that read "mistakenly assigned a _positive_ value to the charge carriers that we now call electrons"?

lilgreenland9• 7 years ago

Nope! It's kinda silly. We all call electrons negative because of how they were labeled 250 years ago. If he had labeled them positive the math involving electric current would be a bit easier.

https://xkcd.com/567/

klyrs• 7 years ago

I ran into this recently with vacuum tube diodes. There's a cloud of electrons surrounding the heated ground-plate. The source plate is at high voltage. Increasing the voltage on the grid attracts electrons, which stream from the ground and fly towards the "source." And I'm calling it "source" because the stream of electrons flowing from ground to source is a positive current from source to ground. Thanks, Ben

aivisol2• 7 years ago

Your notes are awesome. One thing I never thought of (and still have a doubt): can you really say that adding more resistance physically slows down the electrons? I mean, how slow can you make them move then by adding mega or giga ohm resistors? In metres per second? Isn't it more like that by adding more resistors there are less electrons which are able to pass it, which makes current flow less (not slower)? Just a random thought, without research.

sandworm101• 7 years ago

Electrons move at the same speed. In a low-resistance material (metal crystal) they move in an almost strait line. In a higher resitance material they take a longer path, and must line up (stop) to make it through bottlenecks. They only seem to be moving more slowly at a macroscopic level.

lilgreenland9• 7 years ago

I'm also speculating here, but I think resistance can manifest as slower electrons or as fewer electrons moving at the same speed.

On the wire, away from the resistors, the number of electrons that can move should stay constant, so the election drift velocity should drop as resistance increases.

https://en.wikipedia.org/wiki/Drift_velocity

https://codepen.io/lilgreenland/pen/xprGvr (not a mobile friendly link)

One more thing to add. Electron drift velocity isn't the same as signal propagation speed. Wires can transmit information at around 2/3 the speed of light, but the drift velocity of an electron in a wire is around walking speed.

neuralk• 7 years ago

Beautifully presented! Thanks for sharing, these notes are inspiring, I especially like the simplicity of the presentation's design paired with interactive elements. Too often I find material with the latter to be extremely busy. As someone interested in instruction, I'm taking notes from this!

negamax• 7 years ago

Just amazing! Imagine all the physics and knowledge from multiple sciences, disciplines and fields are used when someone tells Amazon Echo to turn on a charger or socket that’s connected to a phone or laptop.

Echo -> ISP wires —> Undersea Cables —> Amazon Servers -> Back home -> Electricity flow

And this is so super high level

All of these devices on the way are powered by electricity from dams, solar, wind etc. Before voice to speech hits or data is read. Processors and hard disks must do so much heavy lifting

It’s surreal the level of abstraction we are surrounded by..

aaronblohowiak• 7 years ago

Quite fascinating and mind-boggling. What really blows my mind is that technology is still extraordinarily less complicated than (bi|ec)ology.

geggam• 7 years ago

It's interesting to me when I read it. We take it down to the proton neutron and electron stating they are charged with positive negative or neutral charge.... but what are they charged with ?

Electricity ? What is it made of ?

dreamcompiler2• 7 years ago

It's made of the electromagnetic force. We can measure it and characterize it very accurately with mathematics. We can say what it isn't (gravity or the weak force or the strong force), but we cannot say what the electromagnetic force is. Sorry. If you figure it out you'll get a Nobel Prize.

rnestler• 7 years ago

We can say what it isn't (gravity or the weak force or the strong force)

Isn't the electric and the weak force considered the same force these days? See also https://en.m.wikipedia.org/wiki/Electroweak_interaction

tntn• 7 years ago

They aren't "charged with" anything. Some elementary particles happen to interact with one another in a particular and consistent way, and we label them according to how they behave with something we call charge.

Electric charge is fundamental.

Koshkin3• 7 years ago

We say that a macroscopic body is “electrically charged” when there is an excess (or a lack) of electrons in it - which merely creates a disbalance between the electrons and the protons. We say that an elementary particle is electrically charged to indicate that there is a nonzero probability of it emitting or absorbing a photon (which leads to creation of the electromagnetic force).

asark• 7 years ago

Physics runs out of "why"s somewhere around the question-asking ability of a clever 5-year-old, and becomes "here's the math to describe what happens" the rest of the way. Electric charge and all the other forces (AFAIK) just are.

carapace• 7 years ago

For an exercise in clear (and perhaps provocative) thinking, try:

What is electricity? This question is impossible to answer because the word "Electricity" has several contradictory meanings. These different meanings are incompatible, and the contradictions confuse everyone. If you don't understand electricity, you're not alone. Even teachers, engineers, and scientists have a hard time grasping the concept.
Obviously "electricity" cannot be several different things at the same time. Unfortunately we've defined the word Electricity in a crazy way. Because the word lacks one distinct meaning, we can never pin down the nature of electricity. In the end we're forced to declare that there's no such stuff as "electricity" at all!

http://amasci.com/miscon/whatis.html

Koshkin3• 7 years ago

Analyzing the meaning of words is characteristic to philosophy and is not a sign of “clear thinking.”

HNLurker2• 7 years ago

This is trivial for somebody who studies electrical engineering in highschool

kalado• 7 years ago

Basic introductions of a topic are trivial for people that are studying that topic? Shocking!

What Is Electricity? (2013)

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