Electronics

MoDulus · Joined: 04 Dec 2006 Posts: 7 Location: AZ

I just started learning the basics of electronics. I have a breadboard with (2) 10k resistors and (1) 1.5k resistor in parallel. Working on the math to figure out what should be measurable across them with a multi meter.

So Total Resistance = 1/r1 + 1/r2 + 1/r3

or R= 1/10 + 1/10 + 1/1.5

Being lazy I shift everything to the left one and have

R = 1/100 + 1/100 + 1/15

The LCD being 300
(skipping a lot of math here)

R = 3/100 + 3/100 + 20/15

so multiple the top add the bottom
R = 180/215

Now divide
180 divided by 215 = .83

is .83 the correct answer? or do I divide 215 by 180 to get 1.19?

Or have I really screwed everything up inbetween?

Shaun

MoDulus · Joined: 04 Dec 2006 Posts: 7 Location: AZ

Ok. I think I figured it out. For whatever reason when measuring with the multimeter the other day it wasn't giving me correct readings......so I probably was doing something wrong. I figured out my math is correct, and after taking a reading today they matched up. Hurray! anyways Thought I would say I answered my own issue.

Shaun

neon · Joined: 25 Feb 2006 Posts: 593

NO you din't 1/100+1/100+1/1.5=1.48 total resistance is 1/.686=1.48 1/r1+1/r2+1/3+...1/rxxxx= y total resistance is 1/y=resistance total in parallel.
two R =r1*r2/r1+r2

MoDulus · Joined: 04 Dec 2006 Posts: 7 Location: AZ

Ok...I'd say you totally confused me, but I was already confused in the first place. either way let's see if we can work this out.

Say I have 10k + 10k + 1.5k
putting them in parallel and testing with the multimeter it gave me 1.15 for resistance.

time for my math.

to make life simple I shift all 3 resistors 1 place to the right 10.0k = 100 now and 1.5k = 15.

So the total resistance equation should look like

R = 1/100 + 1/100 + 1/15

We need to find the Least Common Denominator(LCD) now.....right?

In this case 300 is the LCD

so The equation should now look like

R = 3/300 + 3/300 + 20/300

R = 26/300

Since we have been playing with the recipricals this whole time we then swap the places of the numbers

R = 300/26 or R = 11.53.........

Since we had shifted the number 1 place to the right. I now shift it back one place to the left.

R = 1.153

Since I have a cheap multimeter it only reads 2 decimal places so

R = 1.15

Am I missing something? It wouldn't be the first time....REALLY!
I don't have the best math skills and I haven't found anything that actually works through all the steps of having more then 2 resistors in parallel. Thank you for actually looking at this.

Shaun

neon · Joined: 25 Feb 2006 Posts: 593

You don't need a common denominator what for the number whatever it is decimal and that is finaly devided into [1] my confusion is it 1.5k or 1.5 ohms unless you decided to put a K it is 1.5 ohms. And mathematics is the mother of all science you should practice that. Even as i type the computers is concorting [0] ,[1] into somthing that you can understand.And finaly meters are indicators -/+ % acuracy never absolute. EVEN A $1000 DIGITAL METER HAS LIMITATIONS OFN ACURACY. MUST UNDERSTAND THIS.

MoDulus · Joined: 04 Dec 2006 Posts: 7 Location: AZ

First off....Thank you Neon for putting up with my incestant poking at this. I understand this to be a vital thing to understand, and I seem to be failing to totally grasp it. grrrrrrrrr

You said no need to have a common denominator. So to make life hopefully clearer. the resistors are 10,000 & 10,000 & 1500

Would that be

R = 1/10,000 + 1/10,000 + 1/1500

R = 3/21,500
or is it
R = 1/21,500

and from there then what? I could use a good swift kick in the right direction.

Shaun

neon · Joined: 25 Feb 2006 Posts: 593

I will hate for you to ask me about thevenin . it is very simple my resistors this time OK
1K||21K|33|=.001+.0000476+.0312=.03226
1/.03226=30.998 OHMS
22K|23k|24K|25K .0000454+.0000416+.0000416+.00004=.0001686 1/.0001686=5931.1981 OHMS OR 5.9Kgeneraly.
2 resistors can be calculated by simply r1xr2/r1+r2=r3

MoDulus · Joined: 04 Dec 2006 Posts: 7 Location: AZ

hahahahaha........You probably think I'm a complete moron......I do at the moment! Thank You for all your help. It finally makes sense! You breath a sigh of relief now. I have been looking at the 1/r1 as a fraction and not 1 divided by r1.......looking at your example helped it make so much more sense. Thank you for having patience and tolerating me. You have helped extremely.

neon · Joined: 25 Feb 2006 Posts: 593

Now is easy I must remark that i am glad that you follow trough. some else would not. they follow their own agenda and line of thinking and don't deviate.

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