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### Topic: I blew up the parallel resistor formula! (Read 2446 times)previous topic - next topic

#### modeller

##### Feb 28, 2013, 02:20 pm
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!

#### mmcp42

#1
##### Feb 28, 2013, 06:49 pm
au contraire
1/r = infinity so R = 0
notaprob
there are only 10 types of people
them that understands binary
and them that doesn't

#### JimboZA

#2
##### Feb 28, 2013, 06:59 pm
Bzzzzzzzzzzzzzzttttt....

1/0 is not infinity, it's undefined.
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### retrolefty

#3
##### Feb 28, 2013, 07:01 pm

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

#### Grumpy_Mike

#4
##### Feb 28, 2013, 07:08 pm

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.

Quote
and the formula blew up!

No it didn't.
Have you come across the term GIGO?

#### modeller

#5
##### Feb 28, 2013, 07:10 pm

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.

#### JimboZA

#6
##### Feb 28, 2013, 07:13 pmLast Edit: Feb 28, 2013, 07:20 pm by JimboZA Reason: 1
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...
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### retrolefty

#7
##### Feb 28, 2013, 07:13 pm

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

#### modeller

#8
##### Feb 28, 2013, 07:36 pm

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?

#### Jack Christensen

#9
##### Feb 28, 2013, 07:53 pm

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.

#### modeller

#10
##### Feb 28, 2013, 08:08 pm
Wait till you see the Zero volt battery I have.

#### mmcp42

#11
##### Feb 28, 2013, 08:41 pm
b

Bzzzzzzzzzzzzzzttttt....

1/0 is not infinity, it's undefined.
but infinity is pretty close!
there are only 10 types of people
them that understands binary
and them that doesn't

#### Grumpy_Mike

#12
##### Feb 28, 2013, 10:21 pm
Quote
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.

#### modeller

#13
##### Feb 28, 2013, 11:37 pmLast Edit: Feb 28, 2013, 11:47 pm by modeller Reason: 1

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)

#### Grumpy_Mike

#14
##### Mar 01, 2013, 12:14 am
Quote
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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