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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)

#91

Post by ambrop7 »

seiferteric wrote: post #49
justifier wrote: post #35

Earlier quoted context omitted.

From the linked notes: I never really understood capacitors until I started trying to construct proper water-analogies for them. Then I discovered that my electronics and physics classes had sent me down a dead-end path with their garbage about "capacitors store electric charge." Since my discovery, I've gained significantly more expertise in circuit design, which leads me to a sad thought. Maybe the more skilled of…

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)

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

#92

Post by syncsynchalt »

hyperliner wrote: post #21

Whaaat? Electricity does not flow at the speed of light? OH THE HUMANITY!!!!

Electric potential travels at nearly the speed of light, the electrons themselves do not (they flow at a rate proportional in some way to the amount of potential, iirc).

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

#93

Post by 127 »

WalterBright wrote: post #76

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.

As a hobbyist and a complete beginner, you can do surprising amount of stuff just by memorizing U=RI and P=UI. Through a closed loop current is always the same. Through a closed loop voltage drops must equal the voltage source.

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

#95

Post by esmi »

justifier wrote: post #35
notalaser wrote: post #16

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…

From the linked notes: I never really understood capacitors until I started trying to construct proper water-analogies for them. Then I discovered that my electronics and physics classes had sent me down a dead-end path with their garbage about "capacitors store electric charge." Since my discovery, I've gained significantly more expertise in circuit design, which leads me to a sad thought. Maybe the more skilled of…

People say "capacitors store electric charge" because that's how the integral form of the capacitor equation works. [1] When tutoring EEs in university I spent a lot of time getting them to unlearn water analogies. They break down in some very fundamental ways. [2] I agree the analogies are useful when introducing the concept of capacitance and inductance but to me the analogies are the dead-end path.

[1] http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capeng2....

[2] https://en.wikipedia.org/wiki/Hydraulic_analogy#Limits_to_th...

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

#96

Post by ghaff »

tantalor wrote: post #60
rubberstamp wrote: post #58

Earlier quoted context omitted.

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

Capital is what you owe your investors, eg "startup capital". Sometimes this is called equity.

That may well be true in some startup contexts but, more generally, capital (more typically called equity) is effectively whatever is left over after you subtract your liabilities (accounts payables, short- and long-term debt, etc.) from your assets. This number shows up on the same side of the balance sheet as liabilities.

A balance sheet doesn't really speak to who might have claims to ownership of the company under what terms and the dollar amount of equity on the balance sheet doesn't imply that investors are owed that specific dollar amount.

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

#97

Post by Asooka »

anu7df wrote: post #71
nilkn wrote: 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…

I am all for introducing things the correct way, but this example of yours just does not work for me. Fractions as equivalence classes? or as a solution to an equation. No. That might work for you. In fact I might even argue that it only works for you - the child idealization created by "current you". There are many things wrong with US education. But I do not think introducing fractions using concrete examples is on…

Children take a long time to realise that one half of pizza is the same as two quarters. In general you can give a child less pizza and as long as it's the same number of pieces, they can't tell the difference. The well-known experiment is with presenting two sets of pieces of chocolate, one with less chocolate but more pieces and most children say the one with more pieces has more chocolate.

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

#98

Post by palunon »

bandrami wrote: post #86
notalaser wrote: post #16

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.

Holy crap. It all make sense now. Thank you !

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

#99

Post by tantalor »

JadeNB wrote: post #87
tantalor wrote: post #72

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…

No, "they" is always the bank (or whatever business manages the account). By "they deposit into it", I meant the bank adds funds to your account.

It doesn't matter whether you are a business owner; your bank account is still an asset to you and a liability to the bank.

Personal & business accounting are the same, except your only investor is yourself, so you don't have to manage capital accounts.

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

#100

Post by fzzzy »

notalaser wrote: post #88
fzzzy wrote: post #48

Earlier quoted context omitted.

> 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)

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.

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.
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