ProductSum

Product Sum

Substitution Algebra

Product Sum

Cross Multiplication

Proportion

Efficiency

kW kVA pf

Inductance in Series

Inductance in Parallel

Capacitance in Series

Capacitance in Parallel

Powers Roots

Derivations

Reference Formulas Appendix

Formulas Home

Electrician Math Home

Electrician Education Home

Product Sum Calculation

More as a practice of mathematics manipulation of formulas, product sum is included in these electrician math web pages.

When thee are two resistances in parallel, the total resistance is the product of the two resistance values divided by the sum of the two values.

For example, if there are two resistors in parallel that are, say, 4 ohms each. The product of 4 times 4 is 16 divided by the sum of 4 + 4 which is 8.

So 16 divided by 8 is 2. Or to use the formula for when all resistors are the same value, the value of any resistor - 4 ohms - divided by the number of resistors - 2 - equals 4 divided by 2 or 2. Got it?

Here's the formula:

Rt = R1 times R2 / (R1 + R2)

Find practice problems HERE.

Find audio support HERE.

Another neat calculation for resistors in parallel deals with a circumstance when they all have the same value.

The formula for determining resistance total when all resistors are the same value is the value of any one of the resistors divided by how many there are.

Rt = R1 / N

where Rt is resistance total, R1 is the value of a single resistor, and N is how many there are all connected in parallel.

Find practice problems HERE.

Find audio support HERE.

Many electrician workbooks and practice exams are now available 
as digital downloads for immediate use. 
Click HERE to see what is available.

Products For Sale
2006-2011 David U. Larson
dularson@bellsouth.net
Companion Website to ElectricianEducation.com ,
2011NEC.com and
TechnicianEducation.com
Other websites by David U. Larson which may be of interest:
VisitEuropeOnline.com

OldPostcardsForSale.com
StampDealerLots.com 
HouseFlipGuide.com
SwedenRoots.com
GreenfieldVillageOnline.com
6901st.org