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Why is electricity so hard to understand? (1989)

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Re: Why is electricity so hard to understand? (1989)

#101
post #80

Earlier quoted context omitted.

Cohesion is not an inverse-square field

gp> because water does not attract other water in any way though i was merely addressing this quote your comment confuses me both in fillip and content from cohesion wiki(o): Water, for example, is strongly cohesive as each molecule may make four hydrogen bonds to other water molecules in a tetrahedral configuration. This results in a relatively strong Coulomb force between molecules. from coulomb force wiki(i): Coul…

Yes I knew water attracts water, but it is not relevant to the capacitor analogy. You might as well have said water attracts water via gravity, it's just not relevant in this situation.

Re: Why is electricity so hard to understand? (1989)

#102
post #52

What's the difference between ionized hydrogen and electricity?

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.

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.

Re: Why is electricity so hard to understand? (1989)

#103
post #87

Earlier quoted context omitted.

For the "we debited your account" terminology to be correct, you must consider it from the perspective of the other party. For example, suppose you go into the bank and withdraw $10 and they charge a $1 fee. The transaction looks like this: * Credits: $1 (bank income), $10 (bank assets) * Debit: $11 (customer liability) So when you get your account statement, it will say "$11 debit", because from their perspective, i…

I know that this isn't the point of this thread, so I'll stop after asking one more question. (This may be a terminally wrong-headed question, and I apologise in advance if so.) Despite your very clear explanation, I'm still confused by: > > But it gets even more confusing when they say "we credited your account" or "your account was debited". > From your business's perspective, your bank account is an asset, so when…

The main source of confusion here is that "your bank account" is actually two different entities whose numeric value happens to be the same:

1) On your books, it is an asset account. 2) On the bank's books, it is a liability account.

When a bank says "your account was debited", they are talking about entity #2. That is, "the account on our books associated with 'you'".

But when you yourself think of the account, you think of thing #1.

Let's say you deposit some cash into your account at the bank. That means you are lending the bank the money (extending it credit). The bank records this as two transaction entries:

* A debit (receiving money) transaction which places more money into their general "money we have" pool: you gave them money.

* A credit (owing more money) transaction: they now owe you more money. This increases the amount of what the bank thinks of as "your account".

The statement they send you at the end of the month only shows the second transaction, because that's the one relevant to "your account" in the sense of #2 above.

If you were keeping books on your side, you would likewise record this as two transaction entries:

* A debit (receiving money) transaction for your bank account (now in the sense of #1 above).

* A credit (having less money in an asset account) transaction for your wallet.

So the upshot is that in the two entities that "your bank account" corresponds to, a debit for #1 is a credit for #2 and vice versa. And when the bank sends you a statement, it describes #2, not #1. Since most people don't interact with the terms "debit" and "credit" normally, this is the only exposure they have to those terms, so they learn them backward....

Re: Why is electricity so hard to understand? (1989)

#104

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.

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.

Re: Why is electricity so hard to understand? (1989)

#105

Earlier quoted context omitted.

i agree, I linked more for the similarity in experience between the gp and the author in regard their unlearning I prefer your clarifications when considering the function of capacitors That said, water does attract water.. the term used to describe the phenomena is cohesion https://en.m.wikipedia.org/wiki/Cohesion_(chemistry)

What if the iron sphere contained an osmotic membrane?

i think you could have some fun with this idea

the op author likens voltage to pressure(o)(i) within the water analogy and your osmotic membrane(ii) functions as a sort of pressure responsive valve

i'm sure there are some mental acrobatics to describe a capacitor's relationships: Q=CV; between charge(Q), capacitance(C), and pressure..er, voltage(V) using osmotic principles in place of the capacitance variable addressing the permittivity of the dialectric(iii)

but you'd have to describe osmotic pressure while waving away incongruencies between the two concepts and i think you'd end up so deep into enervated analogies it would just be better to explain in direct language ;P

(o) http://amasci.com/miscon/voltpres.html

(i) http://amasci.com/miscon/voltage.html

(ii) https://en.wikipedia.org/wiki/Osmotic_pressure

(iii) https://en.wikipedia.org/wiki/Capacitance

Re: Why is electricity so hard to understand? (1989)

#107

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 activel…

Intuitive but wrong (and doggedly persistent) idea #1: "electric current is moving electrons". It is moving photons, exciting (largely) stationary electrons. I can't stress how crucial overcoming that misconception was when I was doing EE.

Ehhhhh. Not really. It is the rate of charge passing through a cross-section. That's how it's defined, and as an EE student, what you're saying made little-to-no sense to me.

Re: Why is electricity so hard to understand? (1989)

#108
post #91

Earlier quoted context omitted.

Not really sure I like that link. He seems to suggest that capacitors store "energy" instead of charge, which is just as ambiguous really. It's not like there is some sort of energy particle either. Of course what's really happening is that you are creating an electric potential between two plates. It's true that the net charge is the same, but you are moving electrons from one plate and forcing them (doing work) int…

My water analogy for a capacitor is a piston with pipes attached to both ends, with a spring system that pushes the piston towards the center position. Is that not a mathematically correct equivalent? (in an idealized system with no water resistance/inertia and disregarding that the piston is of fixed length - not that real capacitors have zero resistence, inductance or can store infinite charge)

Or just a membrane between the two sides?

Re: Why is electricity so hard to understand? (1989)

#109
post #82
post #56

Earlier quoted context omitted.

I still remember struggling with fractions when I was young. The funny thing is that I ended up majoring in math in college (at a highly ranked one at that), and I did very well, even publishing research in differential topology as an undergrad. How can someone who struggled to even grok fractions end up being successful in pure mathematics? I think it's because all my teachers operated off the assumption that kids c…

You're pinning too much on supposed bad teachers, and not enough on your past-self's youthful incomplete understanding. 1/2 of a pie is 2/4 of a pie, 2 slices of four is the same fraction as 1 slice of 2. It's exactly the same idea as the equivalence classes, where the ratio matters but the description does not. You just didn't understand that at the time. > the very idea of discussing solutions to an equation will n…

Similar problem from a local school: "__ - 9 = 9"

The teacher would accept 9 or 0 as an answer, not 18. A parent (with math degree even) who was volunteering pointed out that 18 is correct. The teacher ruled against this, arguing that 18 was unacceptable because math with 2-digit numbers hadn't been covered yet.

This was at a "good" school, in a county full of nerds.

Such logic. Poor kids... and people wonder why kids hate math and give up on it.

Re: Why is electricity so hard to understand? (1989)

#110

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

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

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.
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