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Self Induction explanation #128938 04/29/04 01:32 PM
Joined: Feb 2004
Posts: 115
Haligan Offline OP
In voltage induced in an AC circuit, the C-EMF is moving 90degrees out of phase with the applied current.
Voltage leads current.

Here's where I've hit a brick wall. The analogy I learned a long time ago is- voltage is like the water pressure in a pipe, and current is the speed of the flow.

How can pressure (voltage) lead speed (current)? Speed and pressure are both acting on the same electrons. To me, the "charge" can only be in one place at a time. If the inductive reactance creates a new row of balls that are out of phase then okay, but I still can figure out how you can separate Voltage and Intensity.

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Re: Self Induction explanation #128939 04/29/04 05:23 PM
Joined: Jan 2004
Posts: 79
cavo148 Offline
I would think in that analogy that current is the volume or amount of water where voltage is the pressure or force moving it. Also, anything that would constrain the flow of the water would be resistance. Now, take another shot at that brick wall.

Re: Self Induction explanation #128940 04/29/04 06:30 PM
Joined: Feb 2004
Posts: 115
Haligan Offline OP
Now let's figure out how voltage can lead current in an AC circuit with inductive reactance.

Re: Self Induction explanation #128941 04/29/04 06:39 PM
Joined: Dec 2001
Posts: 300
maintenanceguy Offline
The water pressure/flow rate analogy is a pretty rough anology...I wouldn't depend on it being more than a general guide.

However, in a pipe, changes in flow rate will lag behind changes in pressure because of the momentum of the water. When I stomp on the gas, it takes a few moments for my truck to get up to the corresponding speed. It takes a few moments for the water in a pipe to accelerate to the flow rate that matches the pressure too.

The lag between voltage and current is mostly a result of magnetic fields being created by the current flow and those magnetic fields fighting changes in the current that created them. Ufortunately this is one of those areas you just have to take on faith unless your math skills are a whole lot better than mine.

Re: Self Induction explanation #128942 04/29/04 09:38 PM
Joined: Feb 2004
Posts: 115
Haligan Offline OP
Hey, thanks. The car analogy helped. It kinda picks up where the water pipe left off.

One of these days I'm going to take my top 3 head-scratching questions to an electrical engineering professor at the university down the street. Maybe we can go for a beer. Or tea.


Re: Self Induction explanation #128943 04/30/04 06:35 AM
Joined: Dec 2001
Posts: 300
maintenanceguy Offline
Edit: repeated info. wasted space.

[This message has been edited by maintenanceguy (edited 04-30-2004).]

Re: Self Induction explanation #128944 06/24/04 04:50 AM
Joined: Jun 2004
Posts: 176
PEdoubleNIZZLE Offline
Current is how many electrons flow through the circuit. I believe 1 Ampere is 6,280,000,000,000,000 (6.28 quadrillion) electrons per second.

Voltage is the potential difference from 2 reference points in a circuit (usually the leads of a component or power supply). This is the force that pushes the electrons through a resistance. The more force, the more electrons. I can't go into any more detail from here, except for ohm's law.
Hope this helps!


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