Can a LRC circuit produce a net magnetic field with zero net charge flow?

AI Thread Summary
The discussion centers on whether an LRC circuit can produce a net magnetic field with zero net charge flow. The initial analysis suggests that alternating current can create a time-averaged squared magnetic field, potentially allowing for work without net charge movement. However, participants point out mathematical errors in the calculations regarding the squared magnetic field, specifically the treatment of negative currents. The conversation also touches on the implications for systems like AC induction motors, which operate effectively despite zero net charge flow. Ultimately, the consensus leans towards the idea that a system with zero net charge flow can indeed perform work, countering the original claim.
kmarinas86
Messages
974
Reaction score
1
Let's say for the:

First 10 milliseconds: Current is 1 milliamp. The squared magnetic field resulting we will call "default".

1 millisecond following, last millisecond: Current is -10 milliamps. The squared magnetic field is -100 * "default".

The time average square of the magnetic field corresponds to: 10 * 1 - 1 * 100 = -90

One could then imagine the ability for an electromagnetic field made this way to do net work with zero net charge flow, provided that the time constant of the wire is larger than 10 milliseconds. Capacitors could easily increase the time constant of the circuit. The capacitors could be lined up in circuit with a low voltage battery. The circuit could intermittently connect and disconnect a higher voltage, higher current battery with the opposite polarity for a fraction of the time. If timed precisely, the charges would travel back in forth through the wire in a linear way while producing time-average squared magnetic field that is positive.

Something is wrong.
 
Engineering news on Phys.org
kmarinas86 said:
Current is -10 milliamps. The squared magnetic field is -100 * "default".

The time average square of the magnetic field corresponds to: 10 * 1 - 1 * 100 = -90

Something is wrong.

One thing that is wrong is that the square of -10 is +100, not -100.

The rest of your post is difficult to follow. I can't tell what you're trying to say.

Does this have something to do with an earlier post where you were putting the primary and secondary of a transformer in series with a motor and commutator?

It would help if you would provide a schematic (not a picture, but a regular schematic) and tell us what you're trying to do.
 
The Electrician said:
One thing that is wrong is that the square of -10 is +100, not -100.

Right. But this misses an important part of my point of flipping the sign. Let's go with the positive sign and see what happens:

kmarinas86 said:
Current is -10 milliamps. The squared magnetic field is -100 * "default".

The time average square of the magnetic field corresponds to:

10 * 1 + 1 * 100 = 110

To take the average we get:

110/11 = 10

So we get a net squared magnetic field without a net flow of charge.

The Electrician said:
Does this have something to do with an earlier post where you were putting the primary and secondary of a transformer in series with a motor and commutator?

No

The Electrician said:
It would help if you would provide a schematic (not a picture, but a regular schematic) and tell us what you're trying to do.

Right now I'm not trying to do anything. I just need proof that a system that has 0 net charge flow can't do net work.
 
kmarinas86 said:
So we get a net squared magnetic field without a net flow of charge.


Right now I'm not trying to do anything. I just need proof that a system that has 0 net charge flow can't do net work.

You won't find any such proof because it isn't true. In fact, it would appear that you have just proved that it isn't true.

If it were true, then AC powered induction motors wouldn't work.
 
Very basic question. Consider a 3-terminal device with terminals say A,B,C. Kirchhoff Current Law (KCL) and Kirchhoff Voltage Law (KVL) establish two relationships between the 3 currents entering the terminals and the 3 terminal's voltage pairs respectively. So we have 2 equations in 6 unknowns. To proceed further we need two more (independent) equations in order to solve the circuit the 3-terminal device is connected to (basically one treats such a device as an unbalanced two-port...
suppose you have two capacitors with a 0.1 Farad value and 12 VDC rating. label these as A and B. label the terminals of each as 1 and 2. you also have a voltmeter with a 40 volt linear range for DC. you also have a 9 volt DC power supply fed by mains. you charge each capacitor to 9 volts with terminal 1 being - (negative) and terminal 2 being + (positive). you connect the voltmeter to terminal A2 and to terminal B1. does it read any voltage? can - of one capacitor discharge + of the...
Thread 'Weird near-field phenomenon I get in my EM simulation'
I recently made a basic simulation of wire antennas and I am not sure if the near field in my simulation is modeled correctly. One of the things that worry me is the fact that sometimes I see in my simulation "movements" in the near field that seems to be faster than the speed of wave propagation I defined (the speed of light in the simulation). Specifically I see "nodes" of low amplitude in the E field that are quickly "emitted" from the antenna and then slow down as they approach the far...
Back
Top