ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

ECN Shout Chat
Top Posters(30 Days)
Admin 19
Recent Posts
fuse rejectors
by NORCAL. 03/29/17 01:44 AM
Old decora style outlets
by NORCAL. 03/29/17 01:41 AM
NFPA stuff
by gfretwell. 03/28/17 08:08 PM
Anyone hiring inspectors?
by HotLine1. 03/27/17 08:03 AM
ESA Arc flash course
by TheShockDoctors. 03/24/17 10:15 AM
New in the Gallery:
SE cable question
Popular Topics(Views)
231,865 Are you busy
166,747 Re: Forum
160,870 Need opinion
Who's Online Now
0 registered members (), 82 guests, and 9 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#212745 - 02/09/14 10:20 PM Electrical math problems  
kenanderson  Offline
New Member
Joined: Feb 2014
Posts: 4
Florida
Need help with some electrical math. I can't figure out how to insert a scan of my math book to show the problem.

the two resistors in branch A-B of the circuit are of equal value

[img]https://www.facebook.com/photo.php?...2.100000843173265&type=1&theater[/img]

Last edited by kenanderson; 02/09/14 10:35 PM.

Tools for Electricians:

#212748 - 02/09/14 11:12 PM Re: Electrical math problems [Re: kenanderson]  
kenanderson  Offline
New Member
Joined: Feb 2014
Posts: 4
Florida
Ok let's try again, can't edit previous post....
FB won't allow URL linkage I guess....so let's try angelfire

http://www.angelfire.com/fl4/onemininut/num_nine.jpg

problem #9 on the pic


#212749 - 02/09/14 11:30 PM Re: Electrical math problems [Re: kenanderson]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,803
Brick, NJ USA
Ken:
OK the second link works...
You have 5 Ohms written as an answer.

The resistors are of equal value, they are parallel, and 5 ohms is correct.

5 + 7 in series = 12
12 & 12 parallel = 6
(Use two of eq value equals value of one divided by 2)
12/2 = 6

6 +4 in series = 10
10 & 10 in parallel = 5 ohms as answer



John

#212750 - 02/09/14 11:59 PM Re: Electrical math problems [Re: kenanderson]  
kenanderson  Offline
New Member
Joined: Feb 2014
Posts: 4
Florida
i am working on number 9 also. The rest of the question is as follows:What is the value of each resistor it the ammeter indicates 8 amps?


#212751 - 02/10/14 12:29 AM Re: Electrical math problems [Re: kenanderson]  
Tesla  Offline
Member
Joined: Jun 2004
Posts: 1,273
Sacramento, CA
V = IR

Treat the resistors as if they were one unified value...

I = 8 amps, per your post...

What was the voltage?

Now figure out what your algebra indicates must be the equivalent circuit...

See John's calc's above.^^^

You ought to have Ugly's to hand...

And plainly need to hit the books on first semester algebra.

All electrical problems take these forms.

You might benefit by going to Kahn Academy.

It's free, on the Web, and self-paced.

https://www.khanacademy.org/math/algebra

Perhaps a bit too much at first:

http://www.smps.us/references.html

This is the diagram that's on the cover of Ugly's:

http://www.sengpielaudio.com/FormulaWheel-ElectricalEngineering.htm

I always is used for current ( Unless you're in Physics... then the professor likes to use j.)

R always is used for resistance.

V for voltage is dominant in American usage, E is dominant elsewhere -- again both mean the applied voltage.

For Alternating Current, the voltage always refers to the RMS (Root Mean Square) voltage of the AC waveform.

{ the RMS Voltage x Current in an AC scheme is equal in power to the DC Voltage x Current in a DC scheme. }

Consequently, when these two schemes first met the marketplace, Tesla and Westinghouse pitched the RMS voltage so as to simplfy field calculations -- such as yours.

It was slow going for AC until Tesla published all of the math. Overnight, AC took over long distance distribution. It all came down to the V = IR equation.


Tesla

#212766 - 02/10/14 10:28 PM Re: Electrical math problems [Re: kenanderson]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,803
Brick, NJ USA
As Tesla suggests, you should buy an Uglys book.

Under $20, available at the ECN store right here.

It has all the formulas and 'how to'; you should also have it in the text fromyour class.

Math is very important. 'Basic Electricity' is one of the courses that I used to teach at a County Vo-Tech. I had Uglys as a class mandatory textbook.



John


Member Spotlight
mersadrad
mersadrad
Montreal, Quebec, Canada
Posts: 28
Joined: March 2011
Show All Member Profiles 
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.013s Queries: 15 (0.003s) Memory: 0.7764 MB (Peak: 0.9239 MB) Zlib enabled. Server Time: 2017-03-30 14:41:30 UTC