Basic Electrical Formula's

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Mar 11, 2006 | 09:51 PM

Greywolf

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From: Drummonds, TN USA

Basic Electrical Formula's

P=power, in watts
V=voltage (sometimes shown as "E" for Electromotive Force)
I=current in Amperes
R=resistance, in Ohms

(these are for DC circuits only)

Power Formula's:

P = I times V
P = (I squared) times R
P = (V squared), divided by R

Resistance Formula's:

R = V divided by I
R = (V squared) divided by P
R = P divided by (I squared)

Voltage:

V = I times R
V = P divided by I
V = the square root of (P times I)

Current:
I = V divided by R
I = the square root of (P divided by R)
I = P divided by V

I'll set up a graphic to make the math clearer at some point, but those are the basics.

I'd also like to post a PI chart, but not tonight.

If you think of a formula (such as series and parallel resistance) that would be helpful, please add on.

Please make this post sticky. It will be a fine reference some day...

Please post questions in a seperate thread or by PM so that this is a straight reference to be used by all.

Last edited by Greywolf; Mar 11, 2006 at 09:59 PM.

Mar 12, 2006 | 01:41 AM

Greywolf

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Total Power is additive, regardless if it is in series or parallel. Just add up everything.

WATTS are WATTS

Last edited by Greywolf; Mar 12, 2006 at 01:43 AM.

Mar 12, 2006 | 07:04 AM

Bob Ayers

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From: Durham, NC

Series & Parallel resistance:

Series:

Rtotal= R1 + R2 + R3........

Parallel:

Rtotal= (R1*R2)/(R1+R2)

Mar 13, 2006 | 04:22 PM

Bob Ayers

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Continuation of parallel resistors:

more than 2 resistors....

Rtotal = 1 / (1/R1)+(1/R2)+(1/R3)....+(1/Rn)

Mar 14, 2006 | 07:30 AM

projectSHO89

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From: St Louis

Kirchoff's Law

Kirchoff's Law states that the sum of all branch currents is equal to the total circuit current.

I(total)= I(1) + I(2) + I(3).......

Mar 14, 2006 | 08:05 AM

Bob Ayers

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From: Durham, NC

Thevenin and Norton's Theorem

Don't forget Thevenin and Norton's Theorem's:

http://hyperphysics.phy-astr.gsu.edu.../thevenin.html

http://hyperphysics.phy-astr.gsu.edu...ic/norton.html

Mar 14, 2006 | 10:42 PM

Bdox

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[QUOTE=Greywolf]Total Power is additive, regardless if it is in series or parallel. Just add up everything.

When I first glanced at this I thought you were saying 'power is addictive.' Doesn't that just fit in a lot of situations?