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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)

#71

Post by anu7df »

nilkn wrote: post #56
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…

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 one of the problems. Of course for each his own and in all fairness it is also how the analogy is worded exactly. If I explain 1/2 and 2/4 using pie or pizza slices and ask you how "much" pizza did you get, I think the equivalence idea clears up quite nicely.

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

#72

Post by tantalor »

JadeNB wrote: post #68
tantalor wrote: post #30

Earlier quoted context omitted.

Yes, that is a prime source of confusion for those terms! The problem is all about perspective. From the perspective of the bank, your account is a liability , so when they deposit into it, then its value increases, hence "credit". When they say "your account" they actually mean "the account where we track how much money we owe you". From your business's perspective, your bank account is an asset , so when they depos…

> > 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 they deposit into it, then its value increases, hence "debit". But what you're describing (a business depositing money into your account) is not what I, as a non-business owner, understand by "your account was debited". Businesses with w…

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, it was a debit, i.e., their liability went down. If that doesn't make sense, think about how you pay your own credit card bill (a liability): you take money from (credit) your checking account and send it (debit) to your creditor.

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

#73

Post by mjevans »

Animats wrote: post #69
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…

A practical impact of this - tool users from metric countries don't think in fractions. The notion that the next larger wrench after 1/8 is 5/32 is alien to people brought up with the metric system. Metric bolt heads are integral numbers of millimeters.

The irrational part of this is that the 'wrench system' is actually sized in 32nds of an inch, and thus would be much easier to comprehend with 'improper fractions'.

4/32, 5/32, 6/32, 8/32 ... etc

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

#74

Post by 0x0 »

rubberstamp wrote: post #58
tantalor wrote: post #22

Earlier quoted context omitted.

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 & cre…

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

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)?"

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

#75

Post by kmill »

nilkn wrote: post #56
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…

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 have some memories from first grade in a California public school (in Santa Cruz) of "finding a number we can put in place of x so that x + 2 = 4" and how "at some point you will learn how to deal with x + 4 = 2". In 3rd grade we explored prime factorizations, and I also remember an emphasis on clearing out greatest common divisors for fractions -- so, while it didn't encourage thinking of fractions as equivalence classes, it at least encouraged comparing things by canonical forms. I even remember around then an introduction to base four representations, probably to illustrate the "carry the ten" when adding.

My experience, in contrast to yours, was well-meaning teachers drilling the algorithms while hinting at some underlying structure. I suppose it was enough inspiration to figure out what math was about, and I eventually found myself in a math PhD program. (Despite the fact I had a hard time remembering the so-called "math facts." During competitions, I would try to calculate, slowly, something like 7 x 9 using something like (8 - 1) x (8 + 1) = 8 x 8 + 8 - 8 - 1, since the only "facts" I ever remembered were multiples of five, 6 x 8 and 8 x 8. Those competitions did make me think I was a bit bad at math!)

Though, let me share my story about fractions. In fifth grade, I got a day planner because the school pushed for everyone to get one, and in the front leaves there were various references, like a periodic table, lists of equations, etc., and one which caught my eye was "a/b + c/d = (ad+bc)/bd". For some reason I thought "oh, that is what fractions are" and I tried to explain to a teacher how this defines fraction addition, how finding a common denominator is just a way to calculate this, but instead I was told I was incorrect, and you just find common denominators. I can't say I didn't feel somewhat vindicated when I learned, much later, about the Grothendieck construction.

I also remember trying to find a formula for triangular numbers in sixth grade, and I will never forget the look of horror on my "home-room" teacher's face as she backed away while I explained what I was trying to do.

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

#77

Post by gohrt »

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.

those cards are jokes, right?

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

#78

Post by nilkn »

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…

It's fine if this wouldn't work for you. Nothing works for everyone, and that's sort of the point. Kids are funneled through an extremely rigid sequence of topics focusing entirely on rote application of manipulative techniques. Anyone who doesn't conform to this sequence is just left to painfully deal with it on their own.

I remember a bit later in school I discovered algebra on my own and became really interested in it. I asked if I could take a class on algebra ahead of schedule and was virulently refused by the school counselor, who scoffed at the very notion and declared it to be impossible. Her response was so indignant that it offended me very deeply and caused me more or less to rebel against school in general. I ended up turning away from math completely for many years and didn't come back to it with any real interest or passion until I was about to graduate high school.

> If I explain 1/2 and 2/4 using pie or pizza slices and ask you how "much" pizza did you get, I think the equivalence idea clears up quite nicely.

Sort of. But childhood me would have just told you that, no, in one case I got one big piece and in the other case I got two smaller pieces. Combined they might have the same mass or the same number of calories or the same area, but the numbers you just gave me don't have units and can't be measures of area since they're independent of the radius of the pizza.

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

#79

Post by gohrt »

robbrown451 wrote: post #50
seiferteric wrote: post #49

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…

I think you are missing the point of the water analogies. It is what made electricity make sense to me as well. But don't take it too literally, it's an analogy, not an identity. If you start with things like "a motor is like a turbine, a generator is like a pump, a battery is like an elevated tank", a lot of things can fall into place. The point is you can visualize it.

It's hardly fair to say that water analogies are good but "capacitors store charge" is bad, they are both weak analogies

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

#80

Post by gohrt »

justifier wrote: post #64
seiferteric wrote: post #49

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…

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)

Cohesion is not an inverse-square field
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