Power Division

Lets see: first add R1 and R2 (Rtotal) secondly find E/(R1+R2) (I) thirdly square the above (I^2) fourthly multiply the result by R1 to get P1 fiftly , do it again using R2 to get P2 To find P1 using your formula requires 1 addition, 2 multiplications( including the squaring), and 1 division.

To find P2- you are explicitly repeating the whole process to double the effort.

- , (as I would expect you to do) you keep the intermediate results -particularly I^2 (whether or not you name them, or not, you put them away where you can get them when needed) All that I have done is to give names to the intermediate results. This requires no mathematical, numerical, or mental, effort (but helps to indicate what they really are). .

As for memorization- when it takes less effort and time to work it out from scratch (using either fundamental principles or more broadly useful expressions) than to look up or memorise a formula- why bother with the latter? That is the case here where a specific formula saves no effort computationally at the cost of loss of understanding and an additional rote item to memorise. Your best tool is your mind, why waste it on rote memorisation of trivia?

You seem to have found my first response confused. To quote:

"Ptotal =I^2(R1 +R2) =I^2R1 +I^2R2 =P1 +P2 so P1/Ptotal =R1/R1+R2 Without knowing I (=V/R1+R2) at least you get a ratio Is this what you want?"

It was not intended as a canned formula but simply to point out an approach- It is now obvious that you wanted a canned formula which avoids any need to understand the bases for the formula- your loss. I could have supplied this but chose not to do so as it was a useless exercise. Note that others had the sense not to bother. Good on them.

Note that the first line says I^2R1 + I^2R2 =P1 + P2 and the second defines I- how is this confusing when it is so obvious? Since it appears to be so -my loss as you apparently had problems with this.

As to math - use what is necessary and no more as you say but in order to get your simple canned formula, someone has to use the math and understand what is going on. I have used no more math (and actually a bit less algebra, because of less algebraic massaging) than you have. I have simply named the intermediate steps which are an integral part of the solution process even if not explicitly set out as such. Unfortunately, circuit analysis IS applied mathematical modelling and mathematics is the language of science -that is a fact of life. One uses the mathematical model which most closely meets the required balance between complexity and accuracy in the particular situation that is being considered.

You might wonder (or not) why I am suspicious of "canned" formulae. It is because I have seen too many cases where people plug numbers into such formulae and believe the results even when they have used an inapplicable formula (Not to mention the tendency to slavishly believe the output of their calculators without remembering GIGO).

I did not say that we had gone beyond elementary DC analysis - we haven't even got off square one in that respect.

I'm not intending to be provocative but, if I am, then be provoked into really thinking and questioning the familiar rote formulae--disagree with me- that's how we both learn and evade Alzeimer's. It is also more fun.

The above answer is, as I expect, confusing -try thinking.

If you want to get into the meat of circuit analysis, fine. otherwise say so. If not, then MYST 4 awaits me-more challenge.

Don Kelly @shawcross.ca remove the X to answer

Don...why bother even to get involved in this..

A guy asks a question...you answer in good faith...and then get criticised for it!

JClause, get off Dons back. After quoting Prof Einstein (not Mr) time and time again out of context I'd think you also would have better things to do than argue over trivia. Don's got more in his little finger methinks than you have in your entire body... enuf said

A cover up by implying I had problems. You clip and rewrite history.

No but you imply so, just as you imply above that I had problems with elementary theory.

See what I mean? Try thinking yourself - about being less provocative. But I suspect that's what you're here for - to show your store of knowledge (which is good) and to imply others can't think, (with the hidden implication that you can), which is not good.

Your challenge is to be less provocative.

JC the elder.

Feel better now?

JC the elder

PS - You said:

"You might wonder (or not) why I am suspicious of "canned" formulae."

But you used two "canned formulae": P1/Ptotal =R1/R1+R2 I (=V/R1+R2)

So then, is it OK to use them in pairs? Or does it depend on who's using them?

JC the elder

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Thanks for the advice.

Note Daniel Indyk misspells *criticized* above same as you. Is this coincidence, since you have a problem with the words criticize and criticized.

From google:

"You have a concept- I have criticised it"

- Feb 2 2004, 7:01 pm by Don Kelly

"I have given you specific targets to criticise"

- Feb 1, 8:15 am by Don Kelly

"If you find fault with the work I have shown, then criticise it"

- Feb 4 2004, 3:10 am by Don Kelly

"It is easy to criticise on the basis of extended knowledge"

- Sep 11 2001, 1:42 am by Don Kelly

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In any event, it is your provocation that I criticize. How about being accountable and comment on the following?

You said: "You might wonder (or not) why I am suspicious of "canned" formulae."

However you used two "canned formulae": P1/Ptotal =R1/R1+R2 I (=V/R1+R2)

So then, is it OK to use them in pairs? Or does it depend on who's using them?

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You said: "you went on about the complexity of Ohms law"

No, this is untrue.

I said "Sorry but this was strung out, messy, and no provision for current"

I did not say ohms law was complex.

You clip and rewrite history.

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Also you said: "Note that the first line says I^2R1 + I^2R2 =P1 + P2 and the second defines I- how is this confusing when it is so obvious? Since it appears to be so -my loss as you apparently had problems with this."

This is a cover up for your messy notation.

Again, you clip and rewrite history.

JC the elder

Simply UKUS. "Criticise" = UK. "Criticize"= US. It's not unusual for right-pondians to use an 's' where left-pondians use a 'z'.

I was going to respond to the question when I first sq it. Then I saw that it was answered well. I thought to myself that that should put an end to the thread. Now, it seems that not only is the horse being beat after it is dead, but the horse's flesh is rotting while enduring continued beatings.

Bill

Thank you.

JC the elder