The Electrical Contractor Network

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

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Sprinklered equipment 26-008
by bigpapa
Today at 04:24 PM
On Delay Relay with Auto Reset
by Potseal
Yesterday at 09:59 AM
Wow, that was close!
by jraef
11/28/16 07:06 PM
Earthquake in New Zeeland
by RODALCO
11/27/16 11:25 PM
Calling all Non-US members!! (Non-US only)
by Tjia1981
11/27/16 06:33 AM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 15
HotLine1 10
Texas_Ranger 8
Trumpy 8
sparkyinak 7
Who's Online
0 registered (), 218 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#127004 - 03/25/01 05:02 PM I gotta Ask?
old Appy Offline
Member

Registered: 03/18/01
Posts: 120
Loc: Auckland, New Zealand
I saw this asked in a newsgroup, it got me to thinking.
Simple circuit a source say 12v a light bulb and a switch, when turn on is it best described as:
The electrons being pushed thru the circuit.
The electrons being drawn thu the circuit.

Top
#127005 - 03/25/01 05:47 PM Re: I gotta Ask?
sparky Offline
Member

Registered: 10/18/00
Posts: 5545
Appy;

i'll go out on a limb here,

how about negative charges seeking positive
while positive seek negative simutanously


Top
#127006 - 03/25/01 08:53 PM Re: I gotta Ask?
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Steve,

Good call!!!
The main consideration would be that there's some opposite polarity involved, or difference in Potential, otherwise current would not flow.

Appy,

To amplify a bit on your message, the better way to word this would be Electrons [or total current flows] would be "pushed" through the connected load by the pressure of the voltage, not through the entire circuit.
EMF [voltage] is the pressure which moves charges through resistances.

Now I'll throw a real monkey wrench into everything

Why do Discharge Lamps [HID, Fluorescent, Neon] require a ballast??
To control the maximum current flowing in the lamp to a certain value.
Without the ballast, the lamp will draw as much current it can, before self destruction.

Here's the clincher - once the current starts to flow, the voltage at the lamp becomes real low - almost swings to negative voltage!!

How is this possible, when such a large amount of current is flowing across something that has no physical connection?? - there's no wire between the two ends of a Fluorescent lamp!!

This will make your head spin when you read about it!

BTW: Arc faults and lightning work this way also!!

Scott SET
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

Top
#127007 - 03/25/01 10:20 PM Re: I gotta Ask?
old Appy Offline
Member

Registered: 03/18/01
Posts: 120
Loc: Auckland, New Zealand
Okay, bear with me here please. saying EMF would infer force or pressure again infers force, while a potential difference would to me appear as something other than force like opposites looking to equal err.. almost a leveling kind of effect?

[This message has been edited by old Appy (edited 03-26-2001).]

Top
#127008 - 03/26/01 02:05 AM Re: I gotta Ask?
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Well, lets see if this makes any sense.

A difference in Potential Energy is needed from a power supply [or similar], in order to have a current flow. EMF, or Voltage, is a resulting effect of the Potential Energy available from the power supply.

The EMF becomes a pressure when applied to a Resistance - an opposition to current flow.

If there is absolutely no opposition to current flow, there will be no need to push current, or any way to build up a pressure in a conductor / circuit, because the charges will migrate and equalize by simple attraction / repulsion. If the source which supplies currents has a continuous amount of available charges [such as an alternator or a battery at full charge], it will allow as many charges to flow as can possibly flow, due to the regeneration of a potential difference.
When the potential difference no longer exists [like the battery completely discharges], the charges are equalized throughout the entire circuit and supply, which results in no voltage or moving currents [although this never will exist completely].

An opposite polarity is not the only thing which will compose a potential diference which causes a current flow - any lower / higher energy level will allow charges to flow, like points in a circuit having the same polarity, but a slightly different level of voltage. This in it's self would fill a 1000 word document to explain!!

The fact that the EMF is a component required to push charges through a resistance is why electrical circuits can be used to transmit Kinetic Energy from one place to another - or simply, electricity can do some work.
Applying the level of current flowing through a given load device [like an incandescent lamp] and at what pressure, is what composes the energy level "dissipated" into the load.
These two factors, figured over a certain time frame, results in the Work being done.

Voltage, or pressure, is built up at the load, so it's a component of resistance.

Going more in-depth from here would require a lot of typing.
I would suggest to you and others, which are having difficulty understanding my examples, obtaining some books in physics and study them for at least a few months, in order to help grasp the terms and details involved.
I do, and will continue to, enjoy discussing this stuff, but I do not want to make it so unreal, or complex, there is a difficulty in understanding stuff - resulting in persons becoming overly confused [not trying to baffle people with bulls--t ].

One great area which would be extremely helpful here would be Electronic component studies and Semiconductor theories.
Not only are they more closely related to the Electrical fields than their physics counter parts, but they make more sense to persons with electrical backgrounds, due to the use of familiar terms and examples.

This would be the most effective way to advance one's theory knowledge base.

Remember, this stuff takes time to understand, so try not to get discouraged if it takes you months, even years, to fully comprehend. It's a field which requires a constant updating of knowledge [plan to never stop studying ]

Hope this made a little more sense.

Scott SET
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

Top
#127009 - 03/26/01 02:40 AM Re: I gotta Ask?
old Appy Offline
Member

Registered: 03/18/01
Posts: 120
Loc: Auckland, New Zealand
Thanks for that Scott i am slowly getting it I think, i enjoy this extra study. In the mean time i will have a stab at ..
"How is this possible, when such a large amount of current is flowing across something that has no physical connection?? - there's no wire between the two ends of a Fluorescent lamp!!
I think its ionisation within the lamp that allows the current to flow.?

Top
#127010 - 03/27/01 06:10 PM Re: I gotta Ask?
Steve T Offline
Member

Registered: 02/14/01
Posts: 312
Loc: Oak Park, IL, USA
There is no "solid" physical connection to be more correct, right? Who said electricity can't flow thru a gaseous connection? It doesn't happen as easily because gaseous substances atoms tend to be farther apart but, when you pressurize gases, the atoms(molecules) are closer together right?
Scott, or anyone who may know, can the molecules of a gas be pressurized to a point that makes it's resistance equal to a solid, such as copper, at sea level pressure?

This is getting into chemistry a little bit but I found the basic college level chemistry I took helped me very much with understanding electricity a little better. It especially helped in understanding how chemical reactions work and how nothing is lost, just changes form.

Top



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals