current flow question

Thread Starter

learneager

Joined Jan 19, 2024
17
Hello, I'm a student and still don't get this. I've learnt that a current flow between 2 points of different electric potential, but I also read that the current only flows in a closed path. I guess the latter is for true only for steady currents, doesn't it? but in the case of AC, will the current flows in an non closed path but between two points of different potential? for example touching an energized metal with AC when I have another potential
thanks
 

BobTPH

Joined Jun 5, 2013
9,149
What is an “energized metal?”

How does one “connect it to an AC?”

You will have to be much more clear in your example.
 

Thread Starter

learneager

Joined Jan 19, 2024
17
for example a faulty line wire inside a toaster that touches the metal frame of it.. that would energize the toaster metal frame
 

ericgibbs

Joined Jan 29, 2010
18,997
for example a faulty line wire inside a toaster that touches the metal frame of it.. that would energize the toaster metal frame
Hi l_e.
The toaster metal work should already be connected to Earth, which should blow the fuse with that faulty wire.

If the toaster was not Earthed, the metal work would discharge through you to ground and back to the mains alternator, you would receive an electrical shock.

E
EG57_ 1416.png
 

crutschow

Joined Mar 14, 2008
34,689
the current only flows in a closed path. I guess the latter is for true only for steady currents, doesn't it? but in the case of AC, will the current flows in an non closed path
The path is always closed for current to flow.
Makes no difference whether it is AC or DC.
 

Thread Starter

learneager

Joined Jan 19, 2024
17
But what if the AC power comes from an unearthed floating-ground generator? there should be no closed path in that case, right? 'my ground' would not be connected to the generator's ground
 

nsaspook

Joined Aug 27, 2009
13,426
Does that apply to an antenna?
Don't open that can of electrons to make some point. :eek:

Antennas are not really a special case in EM. It's just a launcher of the electrical energy away from the guided path of fields surrounding the conductors of flowing charge/currents.

The 'path' doesn't need to be directly associated with the physical charge of a conductor. The electrical energy path is the universe between local currents causing remote currents via fields that self propagate in space or are local reactive fields.
 

ElectricSpidey

Joined Dec 2, 2017
2,834
Don't open that can of electrons to make some point. :eek:

Antennas are not really a special case in EM. It's just a launcher of the electrical energy away from the guided path of fields surrounding the conductors of flowing charge/currents.

The 'path' doesn't need to be directly associated with the physical charge of a conductor. The electrical energy path is the universe between local currents causing remote currents via fields that self propagate in space or are local reactive fields.
I'm not trying to make any damn point.

I'm trying to understand why electrons/charge moving back and forth in a conductor in alternating current is considered "current" but the same movement in an antenna is not.
 

crutschow

Joined Mar 14, 2008
34,689
I'm trying to understand why electrons/charge moving back and forth in a conductor in alternating current is considered "current" but the same movement in an antenna is not.
There is current in an antenna, why do you think there is not?
The current equals the radiated power divided by the antenna RF voltage applied, so that current can be large for a high power radio/TV transmitter.
The antenna appears as a resistive load with the energy radiated as an EM wave.
 

ElectricSpidey

Joined Dec 2, 2017
2,834
I know there is current in an antenna.

But you said the path must always be closed for current to flow.

Maybe closed path means something different to you and me.
 

Thread Starter

learneager

Joined Jan 19, 2024
17
The path is always closed for current to flow.
Makes no difference whether it is AC or DC.
mmm but this is not the case with static current or any DC current.. they just need two points of different potential to flow.. not any closed circuit. Thinking about it, AC current doesn't make any sense if it's not in a closed circuit.. AC won't flow without a closed loop, doesn't it?

You should not be shocked.
I should only be shocked if I touch the 'live' toaster frame and the generator chassis at the same time, right? or if the voltage is high enough to break the separation of the 'two grounds', which is not the case of line voltages

Please correct me if I'm wrong
 

WBahn

Joined Mar 31, 2012
30,243
But what if the AC power comes from an unearthed floating-ground generator? there should be no closed path in that case, right? 'my ground' would not be connected to the generator's ground
For an example, look up any of the many videos of linemen inspecting high-tension power lines by being brought into contact with it via helicopter and then transferring to the line and moving along the line inspecting the cable until they are picked back up by the helicopter.
 

WBahn

Joined Mar 31, 2012
30,243
I know there is current in an antenna.

But you said the path must always be closed for current to flow.

Maybe closed path means something different to you and me.
Imagine breaking a wire and connecting each wire to a plate and positioning the plates facing each other and close, but not touching. Is there a closed path between them?

If not, then what about a circuit branch containing a capacitor, since it is the same thing?

Read up on Maxwell's Displacement Current.

One way to think of it is that changing electric and magnetic fields are a form of propagation medium.
 

nsaspook

Joined Aug 27, 2009
13,426
I'm not trying to make any damn point.

I'm trying to understand why electrons/charge moving back and forth in a conductor in alternating current is considered "current" but the same movement in an antenna is not.
I think you're hung on the mental picture of closed path being a circuit theory conductor wire loop.
1705682072814.png

Eddy currents flow in a closed path.
1705681908503.png
Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field.
 

ElectricSpidey

Joined Dec 2, 2017
2,834
Well by that definition a single electron orbiting a proton is a "closed path".

And I don't see the relevance to the OPs query.
 
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nsaspook

Joined Aug 27, 2009
13,426
Well by that definition a single electron orbiting a proton is a "closed path".

And I don't see the relevance to the OPs query.
Well they don't orbit but if they did ...

Nor do I see the relevance of antennas to the OPs query.

To the OP, a part of the closed loop can be your body capacitance coupling AC/Pulse electrical energy into you, resuling in ionic current flows that can hurt or kill you.

From a truly open to closed path are varying degrees of isolation that depend of several factors.
 
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