
Why is electricity so hard to understand? (1989) - Tomte
http://amasci.com/miscon/whyhard2.html
======
notalaser
I think more than half the time I spent earning my EE degree has been spent
unlearning the intuitive (but wrong) things that I was liberally taught. I was
fortunate enough to have an exceptional Physics teacher in high school, who
managed to avoid a lot of the bullshit that less fortunate students were fed;
sadly, I compensated that with some of my own (misguided) self-study.

This experience also taught me to actively mistrust "intuition" and "common
sense". Not that there isn't value in intuition (quite the contrary, it's
priceless, from design to maintenance), but it's only useful when it rests on
a solid theoretical foundation. _Prior_ to earning that foundation, it's
nothing but a (very bad) shortcut that people take because they want to feel
knowledgeable, but don't want to invest the effort of going through all that
math mumbo jumbo.

~~~
k__
I got it taught about 3 or 4 times, and every time I understood it less.

In middle school they told me, it's electrons moving at the speed of light
through a conductor.

In high school they told me, no no, they don't move at the speed of light,
just when one electron enters the conductor, another one on the other side
will leave the conductor, like with peas in a straw. And this enter/leaf is at
the speed of light.

At university they told me, no no, you got it all wrong, it's about the
electro static and electro dynamic fields which stand orthogonal on each other
and produce electro magnetic waves... what?!

I seriously have no idea anymore.

~~~
notalaser
As far as circuits go, this is about the closest high school Physics gets to
truth (and it's decently close, compared to how wrong it gets e.g.
capacitors):

> In high school they told me, no no, they don't move at the speed of light,
> just when one electron enters the conductor, another one on the other side
> will leave the conductor, like with peas in a straw. And this enter/leaf is
> at the speed of light.

although "entering" and "exiting" the conductor isn't really a good
description.

A better way to think about it is that "conductor" is really just slang for
"material that has a bunch of free electrons and very little room for more".
This is the "sea of electrons" that Beaty talks about. It makes sense that, if
all this sea flows _steadily_ (i.e. at the same rate throughout the
conductor), forcing a change in the rate of flow in one part of the conductor
will be felt almost immediately in another part of the conductor, no matter
how distant, even if the flow itself is extremely slow.

(If you're thinking that this is only true if the "pipe" through which the
"sea" flows is full, you're right, this is how free electrons behave in
conductors; that's why Beaty insists that a good analogy for a conductor is
"like a pipe which is already full of water".

> At university they told me, no no, you got it all wrong, it's about the
> electro static and electro dynamic fields which stand orthogonal on each
> other and produce electro magnetic waves... what?!

If they taught you _that_ , they are most definitely wrong, it sounds loosely
like induction, but with two strange names instead of "electric" and
"magnetic" :-).

This is a better description of the physical reality, and it does help you
understand circuits better if you think about it, but not in a very
_practical_ manner.

~~~
fzzzy
> If they taught you that, they are most definitely wrong, it sounds loosely
> like induction, but with two strange names instead of "electric" and
> "magnetic" :-).

I don't think "definitely wrong" is a good description. electrostatic and
electrodynamic are perfectly good, if somewhat archaic, terms for the electric
and magnetic fields. (E and H fields)

~~~
notalaser
_Ah_. That's a terminology fuck-up on my side, then. I've never encountered
this convention, but classical electromagnetism has almost two centuries of
history behind it. A lot of weird names have been used for a lot of things.

For what it's worth, though, these are terrible names, archaic or not :-D. If
they ever were in use, I'm glad we moved on.

~~~
fzzzy
I'm not sure they are terrible. Electrostatic describes charges at rest,
capable of inducing a voltage across a dielectric. Electrodynamic describes
charges in motion, capable of inducing a current across a conductor. They seem
like apt descriptions to me.

~~~
notalaser
It doesn't sound too bad when you put it that way, and it certainly made sense
back when Ampere introduced the term, but:

* It doesn't match the way we define electrostatics, magnetostatics and electrodynamics. What defines electrodynamics isn't the fact that charges are moving (they're moving if the currents are constant, too, but the magnetic fields produced by steady currents are in magnetostatics' yard) but the interaction of charges and currents (in more formulaic terms, when both charge densities and current densities are present, not only do you get both electric and magnetic fields, as in magnetostatics, but they also vary in time).

* Charges in motion still produce a voltage across a dielectric. Calling the electric field they produce "electrostatic" when the charges are moving and the field is certainly not static.

~~~
fzzzy
Thanks for writing that out! Very interesting.

I guess it all comes down to the fact that a magnetic field does not exist
without an electric current. One way of thinking about it sees it as charges
moving, and the other way of thinking about it sees it as a static magnetic
field.

I guess that's why the terms are archaic!

~~~
notalaser
Indeed. That's why I think it might have made sense back in Ampere's time. The
classification of these regimes (electrostatic, magnetostatic, electrodynamic)
is more recent, and Ampere's own theory of electrodynamics deals more with
what we term "magnetostatic" today.

~~~
wbeaty
I suspect that it corresponds to Newtonian Statics, the study of mass and
forces. It's a subject area; an ignoring of changes. Not a state of nonmoving.
The Newtonian Statics viewpoint involves summation of forces. It may also
involve taking a snapshot at one point in time.

E.g., when a mass above Earth is in free fall, it still obeys Newtonian
Statics: the weight/attraction force, easily analyzed from moment to moment.
The resulting acceleration and trajectory then falls under "Dynamics."

In other words, electrostatics applies to capacitors and to the mechanical
forces produced by electric fields. Even if currents are also present, and
even if the e-fields are changing with time, electroSTATICS still applies. (A
high voltage, high-amperes power line is very "electrostatic," because of the
significant e-fields and resulting phenomena.)

Static Electricity then is a chapter title, with no existence in the real
world. Neither can we fill a box with Newtonian Statics. To be consistent, we
wouldn't say "electrostatic motor," instead call it a capacitor-motor, or an
e-field motor. (Heh, a stretched spring is statically charged! Full of
Newtonian-static energy!)

------
soneca
It looks like interesting content, but I got a little confused by the writing
style and general layout.

A more succinct, clearly defined structure would help me a lot. Each topic
could be clearer on what is wrong and how is the right way.

It would help a lot just to start with a clear: "What is the right definition
of the word electricity?". Then, maybe a "What is "electrical phenomena" and
some examples". "Correct definition and differences of electric charge, energy
and current".

For me personally, a structure that explains what is the right thing first,
then goes on about misconceptions and consequence of misconceptions is much
better.

I became lost while reading this and finished with basically the same confused
and mistaken understanding of what is electricity as I began.

~~~
mannykannot
It turns out that this is not a good link to be starting with: see
[https://news.ycombinator.com/item?id=12901346](https://news.ycombinator.com/item?id=12901346)

~~~
soneca
Much better. I'll spend some on it later

------
wiz21c
Could someone write the same kind of article for chemistry ? That would help
me to accept the fact that I didn't get it at all :-) Oh, while you're at it :
accounting :-)

~~~
tantalor
Accounting in 8 steps,

1\. Memorize this: Assets + Expenses = Liabilities + Capital + Income

2\. Everything is positive, no negative numbers!

3\. For every transaction, Total Debits = Total Credits

4\. "Credit" is source of money, "debit" is destination of money

5\. Assets and expenses increase with debits

6\. Liabilities, capital, and income increase with credits

7\. Expenses and income may only be increased (debited & credited
respectively)

8\. At the end of the accounting period, distribute income less expenses to
capital accounts

Example:

Your business buys a property for 90k with 50k cash down and 10k closing
costs.

Assets: 90k house (debit), 50k cash (credit)

Expenses: 10k closing cost (debit)

Liabilities: 50k mortgage (credit)

Total Credits: 100k

Total Debits: 100k

~~~
rubberstamp
shouldn't the cash be listed as capital instead of asset?

~~~
0x0
So the basic equation is "assets = capital + liabilities".

Capital+liabilities explain how your assets are "covered". Either you owe
someone for the assets (liabilities), or you own the assets yourself
(capital).

Sometimes it's easier to think of this as

"assets - liabilities = capital".

I.e. whatever is left after considering what you owe, you own.

If you have some cash (an asset), then you need to also list it either as a
liability or capital, simply because you must always be able to answer "where
did this cash from? did we borrow it (liability), or do we own it (capital)?"

~~~
rubberstamp
Thanks for explaining it well. I was caught up in the parent post's example
and tried to equate it with the equation given in it. How would the parent's
example look like in balance sheet? I looked at small business example given
in wikipedia, but failed at writing down parents example into assets and
liabilities balance sheet.
([https://en.wikipedia.org/wiki/Balance_sheet](https://en.wikipedia.org/wiki/Balance_sheet)).

------
amelius
Electromagnetics becomes much more elegant when cast in the language of
differential forms. See e.g. [1].

[1]
[http://www.uio.no/studier/emner/matnat/fys/FYS4160/v08/under...](http://www.uio.no/studier/emner/matnat/fys/FYS4160/v08/undervisningsmateriale/Kursmateriell/forms_teaching_warnick.pdf)

~~~
bsder
You can also go the fields route like Feynman would:

[https://mitpress.mit.edu/books/collective-
electrodynamics](https://mitpress.mit.edu/books/collective-electrodynamics)

------
bronlund
In fact, it isn't so hard that they would like you to believe - it just seems
that way when they remove the best parts due to national security :D

You would have to go back to James Clerk Maxwell's original 20 equations to
see what it's all about. Okey, quaternions are kind of hard, I'll admit to
that, but all in all it makes much more sense.

~~~
pjc50
Like QM, doing it analytically clears away misconceptions and gives a
consistent view - but it isn't exactly something you can teach to children.

It's useful to be able to explain things to laypeople and the not
mathematically inclined, which means tightening up the metaphors.

~~~
bronlund
You have a good point, but still, it's easier to explain to children stuff
that makes sense.

I teach my children that we live in a sea of energy and that you can feel it
when you move. It makes much more sense to them than trying explain inertia.

I tell them that of you rotate something, it will make an energy vortex making
stuff seem heavier - and I show them with a gyroscope.

Then I explain that electrons are just like little gyroscopes, but of only
energy. And it all makes sense to them. They don't think it's hard at all.

~~~
pjc50
Those are excellent metaphors which I've never heard anywhere else.

~~~
matthewmcg
They're reminiscent of Feynman's anecdote about his father explaining inertia:

[https://www.youtube.com/watch?v=Zjm8JeDKvdc](https://www.youtube.com/watch?v=Zjm8JeDKvdc)

~~~
phee
"That - he said - nobody knows". It's kind of different from "we live in a sea
of energy". I honestly think inertia is a lot easier to grasp than energy.
It's a phenomenon you can experiment, describe and name, energy is more
abstract.

------
overcast
The real question is, why is this website so hard to understand? Publishing
what looks like someones personal notebook isn't helping the cause here.

~~~
feedjoelpie
Poor selection of link. Fortunately the author saw us and pointed us toward
the articles instead of the raw notes:
[http://amasci.com/miscon/whyhard1.html#def](http://amasci.com/miscon/whyhard1.html#def)

~~~
mannykannot
I am not sure that is a big improvement. I dipped in here, and what I found
was mostly a repetitive litany of complaints.

~~~
wbeaty
The entire essay-collection is a critique of grade-school electricity textbook
chapters, in the USA. (I don't know if the texts in other countries are
promoting the same misconceptions.) To avoid reading critiques/corrections, go
to any other site except mine. Also see:

Am I just a pedantic nitpicker?

[http://amasci.com/miscon/nitpik.html](http://amasci.com/miscon/nitpik.html)

To deeply grasp physics, often one must UN-learn the common misconceptions
which were acquired in our early school careers. The misconceptions in this
list are the ones believed by educators, and taught to students.

------
farright
Like incompressible fluids, electricity is hard to reason about because we
work in a limit that does not obey local causality.

The entire system must be solved simultaneously, and there is not a well
defined "input" or "output". This can be seen from the fact that when we
analyze a circuit we also include the model the power source and the load.

The combination of non-locality and complex boundary conditions makes it hard
to apply ordinary intuition. We would like to say that the power source "does
something" to the circuit but causality actually runs both ways. E.g. if we
have a constant voltage source, then the circuit will determine how much
current flows through the source. If we have a constant resistance load, then
the load will determine how much power the circuit applies to it.

~~~
msie
Thanks+++ I think you nailed my frustrations with electricity!

------
roel_v
Maybe this is the right occasion to re-ask a question I asked some years ago
on stack exchange, but (despite several people trying their best to explain)
still failed to understand the answer to.

So: does electricity have 'mass'? What I mean is, when current flows, is there
a transfer of electrons (or something else) from the power source to whatever
it is send to? And is there a difference between AC and DC?

The context of this question is that the core argument of a legal paper (of
all things) I was reading at the time (on property rights of virtual goods)
hinged on there being a transfer of mass, however small. I wasn't so sure.

(my SE question devolved into a semi-legal argument - I have a law degree, the
context of the question is a lot more nuanced still than the above
description, and is very much tied to some specific 80 year old Dutch case law
- just saying that to point out that a legal argument on whether or not the
question matters won't add much to the discussion.)

~~~
VLM
Information has mass. Not much. Surely charge on a dram capacitor is s bit (oh
the pun) of energy and energy is mass.

An excellent example of electron movement is a DC current in a metal plating
tank or refining tank. Every atom of aluminum or copper or plated anything
took the movement of precisely one electron (simplification because there are
some non-electroplating methods for some base/plate combos, but yeah pretty
much aluminium is a block of solidified electricity)

~~~
roel_v
So take one RAM stick and another, with the exact same physical makeup (I know
this is impossible, but for argument's sake). Now I put some information on
the one, and random noise on the other. Both will have different mass, right
(because there are different amounts of electrons in the capacitors of both)?
Now I put valuable information on one, and I charge all capacitors of the
other (so the second one has very information density, because it can be
'compressed' trivially by saying '4GB of high bits'). The second one will be
'heavier' than the first, right? And then I copy something over that second
one. It's not like there is a 'transfer' of mass from the other medium to the
RAM stack, because there is a net _outflow_ of electrons, right?

------
pjc50
Very comprehensive!

I've occasionally tried to clear up misunderstandings of this kind on
[https://electronics.stackexchange.com/](https://electronics.stackexchange.com/)
, they're a common stumbling point for beginners. Especially speed of
electrons vs. speed of signals.

------
sgdread
I wish academia took more time to explain things in digestible way instead of
dumping loads of dry papers in rigorous form. For instance, my life would be
so much easier if I saw just this thing below [1]. Alternating current
described in complex numbers has so much sense after going through that
material.

[1] [https://acko.net/blog/how-to-fold-a-julia-
fractal/](https://acko.net/blog/how-to-fold-a-julia-fractal/)

------
Tomte
Also (same site): Misconceptions –
[http://amasci.com/miscon/elect.html](http://amasci.com/miscon/elect.html)

------
sunstone
It gets even more fun in semiconductors when the 'particles' become virtual
but no one bothers to mention that part.

~~~
venomsnake
The way holes move in the semiconductor is the pointers of EE.

~~~
simonbarker87
Adding very little to the conversation here but having done a Ph.D. in high-
temperature semiconductors this made me chuckle and is nicely apt. Just like
pointers, though, you can kind of get by with only a very thin understanding
of them for a surprisingly long time.

------
WalterBright
I've always been bemused by EE wallet cards that contain:

    
    
        V = IR
        I = V/R
        R = V/I
    

If an EE does not know this formulas, he isn't an EE. If he understands so
little about algebra that he needs the three forms, he's going to be misusing
the formula.

~~~
phee
Guess like all engineering jobs, sometimes your job is so far from practice
and so involved in regulations, meetings, standards, bureaucracy, reports, a
little refcard with the most basic things can help to quickly reset your brain
for the rare occasion where you need to actually do something.

------
javajosh
Hmm. I learned about E&M theory from Halliday and Resnick, and the practical
stuff from Horowitz and Winfield (The Art of Electronics) and they were pretty
precise about distinctions between electrons, holes, charge, flow of charge,
and so forth. Sounds like I dodged a bullet by _not_ being drawn too much to
electronics as a youth, waiting instead to learn about it as a college physics
major.

~~~
dboreham
Ah, memories of those books too. My Dad was an EE and so I also have memories
of him, on parent-teacher evenings at school, arguing with the physics teacher
about whatever was on the blackboard from the day's lesson..

------
lawpoop
I think the main reason is that we can't physically interact with it with our
hands. We don't play with it as children, the same way we do running water,
throwing rocks, etc. Anything that you can't manipulate or play around with is
very hard to develop an intuitive sense of. It takes a lot of study and
imagination.

~~~
rootbear
I a sense, I DID play with electricity as a kid. My father was an Electrical
Engineer and a Ham Radio operator, so we had "stuff" around the house. I
learned to solder at a young age. Some time ago, I realized that one of the
best toys I had as a kid was the controller for my HO train set. It had a
Speed (voltage) lever and a Forward/Reverse lever. Basically, it was a safe,
variable voltage DC power supply. I could play with switches and flashlight
bulbs and small motors and learn how they work. I've recently gotten back into
Electronics as a hobby and I'm having all sorts of fun with Arduinos and Pis
and such.

~~~
gozur88
But even then it's not the same because you can't actually see the
electricity. You can only see second order effects.

------
mihau
This article is amazing. It helped me to understand things that I were
confused about years ago. Whole website is filled (!) with these kind of
articles [http://amasci.com/ele-edu.html](http://amasci.com/ele-edu.html) !

------
stuartaxelowen
Electricity doors mean one thing: the movement of electrons. There are a lot
of significant ways it manifests, like in static charge and power systems, and
there are a lot of insignificant ways it manifests, but it's still just
electrons moving around.

------
snarfy
I actually like the water model. Here is a transistor:

[http://imgur.com/a/vhrmR](http://imgur.com/a/vhrmR)

It breaks down as an analogy as soon as magnetic fields come in to play, which
is pretty much any AC circuit.

------
LgWoodenBadger
What's the difference between ionized hydrogen and electricity?

~~~
pjc50
As mentioned in the article, referring to "electricity" is kinf of vague.
Ionized hydrogen floating about is a _plasma_ ; a collection of particle with
a positive net charge. Therefore if some H+ ions move in a particular
direction, that will be a flow of charge: an electric current.

Similarly H+ ions in aqueous solution can carry a current, as in electrolysis.

~~~
brandmeyer
No, it doesn't have a positive net charge. In a plasma, the electrons are
still part of the substance, but they are no longer bound to the nuclei, and
are free to move about. Similar to current in an electrolyte, current in a
plasma is the result of electrons moving one direction, while the nucleii are
moving in the opposite direction.

------
syncsynchalt
All those words and it doesn't even entertain my favorite if-i-had-a-time-
machine scenario: EE would be a bit easier if Franklin had swapped positive
and negative.

~~~
wbeaty
Sure it does. You just have to look at the list of articles, not the giant
pile of random notes.

BEN FRANKLIN SHOULD HAVE SAID ELECTRONS ARE POSITIVE? Wrong.
[http://amasci.com/miscon/eleca.html#frkel](http://amasci.com/miscon/eleca.html#frkel)

EE would be much HARDER if Franklin had swapped positive and negative, since
then our confusion wouldn't lead us to shatteing our own misconceptions. We'd
never sit down and figure out what "conventional current" actually is. No,
it's not backwards. And no, electricity is not made of electrons. In acids,
the electric current is entirely a flow of protons. In dirt, oceans, and human
bodies the current is at least two separate flows: clouds of positive ions
passing forwards through clouds of negative ions travelling backwards. With
two opposite charge carriers, what then is the "true" direction of electric
current? What if there are five: +Na, +K, +H, -OH, -CL ?

Cute notion: Ben Franklin's kite string was an acidic conductor, a piece of
twine which becomes insulating in dry conditions, so it's an electrolyte. And
acid conductors have mobile +H ions to carry the current. (What's a hydrogen
atom, with one missing electron?)

In other words, Ben Franklin's kite string is a Proton Conductor.

SO HE GOT THE DIRECTION RIGHT!!!!

:)

He only was wrong in the case of metal wires. In his day, a typical
"conductor" was a small boy hired to hang from silk ropes, to connect the
Leyden Jar to the "Electrical Machine." Or rather than commoners, sometimes
they used chains of Elizabethan royalty, all standing upon insulating stools.

------
carapace
[http://amasci.com/ele-edu.html](http://amasci.com/ele-edu.html) There's more,
lots more. ;-)

------
QuantumGravity
Perhaps Quantum Mechanics has an answer to that question. And if we can deeply
understand our body, we perhaps have understood electricity.

------
m23khan
wish there was a similar website I knew of when I was a EE student -- them
misconceptions were crazy enough that they led me to drop out of EE and move
into comp. science :)

------
hyperliner
Whaaat? Electricity does not flow at the speed of light?

OH THE HUMANITY!!!!

~~~
pjc50
EM radiation moves at the speed of light; electrical fields and signals move
_near_ the speed of light, depending on the surrounding dielectric properties;
electrons in conductors move fairly slowly. Yes, this is kind of confusing.

------
Aardwolf
Dear author of the website: Nice article. Please fix the TOC links on
"whyhard2.html" to point to "whyhard2.html" and not to "whyhard1.html", and
remove the huge whitespace between TOC and content. This was a very confusing
experience and likely others will fall in this trap. Thanks!

~~~
wbeaty
DOH!

Fixed now.

I messed it up last time I was getting slashdotted by reddit and ycombinator,
and everyone was complaining that the raw unedited notes were just a bunch of
raw unedited notes.

Heh, it's still a 1995 gopher-era design, back when we put all our chapters on
a single long page, to compensate for 300/2400b modem speeds. If it was broken
up into many separate pages, you'd be waaaaaaiting for the text to finally
appear.

~~~
Aardwolf
Thank you very much :)

------
selimthegrim
Wires may not be hollow tubes but surely as a EE he knows that most current
flows through the outer shell of the wire?

E: Yes, I was thinking standard AC for household appliances, my bad

~~~
andars
This is not true for low frequency current.

