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 Author Topic: I blew up the parallel resistor formula!  (Read 1160 times) 0 Members and 1 Guest are viewing this topic.
TX
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 « on: February 28, 2013, 08:20:13 am » Bigger Smaller Reset

I tried to use the parallel resistor formula -

1/Rt = 1/R1 + 1/R2 + 1/R3

to calculate a total of three resistors in parallel. One of them was a 270 ohm, and the other two resistors are shown in the attachment and the formula blew up!

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Leighton Buzzard, UK
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 « Reply #1 on: February 28, 2013, 12:49:24 pm » Bigger Smaller Reset

au contraire
1/r = infinity so R = 0
notaprob
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there are only 10 types of people
them that understands binary
and them that doesn't

Johannesburg UTC+2
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 « Reply #2 on: February 28, 2013, 12:59:22 pm » Bigger Smaller Reset

Bzzzzzzzzzzzzzzttttt....

1/0 is not infinity, it's undefined.
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Look here http://electronicsclub.info/ for basic electronics

Left Coast, CA (USA)
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Measurement changes behavior
 « Reply #3 on: February 28, 2013, 01:01:18 pm » Bigger Smaller Reset

I tried to use the parallel resistor formula -

1/Rt = 1/R1 + 1/R2 + 1/R3

to calculate a total of three resistors in parallel. One of them was a 270 ohm, and the other two resistors are shown in the attachment and the formula blew up!

As the teacher once told you in school, you must show your work! Blowing up is like saying your dog eat your homework.

Lefty

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Manchester (England England)
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Solder is electric glue
 « Reply #4 on: February 28, 2013, 01:08:42 pm » Bigger Smaller Reset

Bzzzzzzzzzzzzzzttttt....

1/0 is not infinity, it's undefined.

As the bottom number gets smaller the reciprocal gets bigger, as this number approaches zero the reciprocal approaches infinity. Only the purest of pure mathematicians would agree with you, engineers would say say it was infinity.

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and the formula blew up!
No it didn't.
Have you come across the term GIGO?
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TX
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 « Reply #5 on: February 28, 2013, 01:10:06 pm » Bigger Smaller Reset

As the teacher once told you in school, you must show your work! Blowing up is like saying your dog eat your homework.

You want a picture of my HP calculator display?

If I attempt the first 1/R1 it says Divide by Zero error.
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 « Reply #6 on: February 28, 2013, 01:13:47 pm » Bigger Smaller Reset

Quote
Only the purest of pure mathematicians would agree with you, engineers would say say it was infinity.

Well I am an engineer....

It's trivial to show that for a/b = c and therefore a =bc, if b = 0 there is no value of c which will satisfy the equation a =bc for the case or a <> 0....., not even infinity; all values of c will satisfy the case of a= 0... therefore undefined.

Slightly edited...
 « Last Edit: February 28, 2013, 01:20:43 pm by JimboZA » Logged

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Look here http://electronicsclub.info/ for basic electronics

Left Coast, CA (USA)
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Measurement changes behavior
 « Reply #7 on: February 28, 2013, 01:13:59 pm » Bigger Smaller Reset

As the teacher once told you in school, you must show your work! Blowing up is like saying your dog eat your homework.

You want a picture of my HP calculator display?

If I attempt the first 1/R1 it says Divide by Zero error.

That was simply a user input error, as there are no zero ohm resistor, certainly not a room temperature. Put in the real resistance values and it will work.

Lefty
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TX
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 « Reply #8 on: February 28, 2013, 01:36:53 pm » Bigger Smaller Reset

That was simply a user input error, as there are no zero ohm resistor, certainly not a room temperature. Put in the real resistance values and it will work.

Lefty! I took a picture of two of them so you wouldn't say that they didn't exist!
You mean the color code is wrong?
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Grand Blanc, MI, USA
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CODE is a mass noun and should not be used in the plural or with an indefinite article.
 « Reply #9 on: February 28, 2013, 01:53:08 pm » Bigger Smaller Reset

You mean the color code is wrong?

Absolutely! All color codes are wrong. I think I smell a conspiracy. Quick someone call Mulder and Scully.
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TX
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 « Reply #10 on: February 28, 2013, 02:08:38 pm » Bigger Smaller Reset

Wait till you see the Zero volt battery I have.
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Leighton Buzzard, UK
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 « Reply #11 on: February 28, 2013, 02:41:15 pm » Bigger Smaller Reset

b
Bzzzzzzzzzzzzzzttttt....

1/0 is not infinity, it's undefined.
but infinity is pretty close!
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there are only 10 types of people
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Manchester (England England)
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 « Reply #12 on: February 28, 2013, 04:21:49 pm » Bigger Smaller Reset

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I took a picture of two of them so you wouldn't say that they didn't exist!
It is simply a limitation of the algorithm that the calculator uses. A decent calculator would give you the right answer, however there are very few decent calculators. Ones that don't think a divide by zero is an error. One that had an IEEE maths standard package in it would not blow up.
I suspect you are very young if you believe calculators are the arbiters of what is possible in mathematics.
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TX
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 « Reply #13 on: February 28, 2013, 05:37:59 pm » Bigger Smaller Reset

I suspect you are very young if you believe calculators are the arbiters of what is possible in mathematics.

No, actually I'm 55.

But, now I know why you are called Grumpy Mike.

(pssst - it's a joke thread, that's why it's in the Bar Sport board)
 « Last Edit: February 28, 2013, 05:47:20 pm by modeller » Logged

Manchester (England England)
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 « Reply #14 on: February 28, 2013, 06:14:05 pm » Bigger Smaller Reset

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it's a joke thread, that's why it's in the Bar Sport board
Yes but it is such a bad joke.

Not as good as the way we used to wind up our purchasing department by insisting that they got 1% zero ohm links in place of the rubbish 5% ones they always bought.
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