Shouldn't a wire (coil) just store energy and not give it away?

[ataskaita]

Hello, I was thinking about induced currents in a wire(coil). For example when a current from an external source passes through a wire - the changing magnetic field induces a current opposing the current applied (back emf) like a Newton's 3 law and nothing would ever pass through a wire, but the good part is that the magnetic field produces back emf only when the field is changing, which means that sooner or later there will be no change and no back emf. No back emf - current can flow. Which brings me to the things happening to the wire when the current is stopped: current is stopped, magnetic field collapses and produces current in the opposite direction, but then i think - shouldn't the current produced sort of oppose the collapse of the magnetic field? Or if it can't oppose the collapse of the magnetic field, maybe it can by being created by magnetic field create it's own magnetic field, which would create current, which would oppose the creation of the current creating it and so on, on and on creating back emf, which creates back emf and then a back emf creates again back emf and so on and nothing happens... The first part has some logic, at least for me, because when a current is applied by external source sooner or later the will be no change in magnetic field- hence no back emf and a flow of current, but in the case of a wire, which has energy induced in it in the form of the magnetic field, shouldn't the magnetic field just fight it self and nothing would happen, because of no external current source- any ideas?

 

[technician]

You need to get your logic sorted out.
A changing magnetic field produces an induced emf, (not a current), the direction of the induced emf opposes the change in the magnetic field (not the current applied).
Newtons 3rd law has nothing to do with induced emfs.

 

[Drakkith]

Which brings me to the things happening to the wire when the current is stopped: current is stopped, magnetic field collapses and produces current in the opposite direction, but then i think - shouldn't the current produced sort of oppose the collapse of the magnetic field?

This is incorrect. When the current begins to stop, the changing magnetic field generates an EMF that tries to keep the current flowing. Thus energy is stored in the magnetic field and delivered to the wire as EMF that causes current to flow after the external power source is removed.

 

[ataskaita]

This is incorrect. When the current begins to stop, the changing magnetic field generates an EMF that tries to keep the current flowing. Thus energy is stored in the magnetic field and delivered to the wire as EMF that causes current to flow after the external power source is removed.

OK, back to textbook:D

 

[PJC01]

I understand your thought process and concerns regarding induced currents in a wire. However, it is important to note that a wire (coil) does not just store energy, it also has the ability to transfer energy. This is due to the principles of electromagnetism, specifically Faraday's law of induction.

When a current from an external source passes through a wire, it creates a magnetic field around the wire. This changing magnetic field then induces a current in the opposite direction, which is known as back electromotive force (back emf). This back emf opposes the current applied and can limit the flow of current through the wire. However, this does not mean that the wire cannot transfer energy. In fact, the wire is still able to transfer energy in the form of the induced current.

Furthermore, when the external current is stopped, the magnetic field around the wire collapses and produces a current in the opposite direction. This is known as self-inductance. This current does oppose the collapse of the magnetic field, but it does not create a never-ending cycle of back emf. This is because the energy of the collapsing magnetic field is converted into electrical energy, and this energy is eventually dissipated as heat.

In short, a wire (coil) does have the ability to store energy in the form of a magnetic field, but it also has the ability to transfer this energy through induced currents. The back emf and self-inductance effects do not create an endless loop, as the energy is eventually dissipated. I hope this explanation helps to clarify any confusion you may have.

 

[PJC01]

I can provide some clarification on this topic. First, it is important to understand that a wire (or coil) does not just store energy - it also has resistance. This means that when a current flows through a wire, some of the energy is lost as heat due to the resistance of the wire. So, even if there is no back emf, the energy in the wire will eventually be dissipated as heat.

Secondly, the phenomenon you are describing is known as self-inductance. This is when a changing magnetic field induces a current in the same wire that produced the magnetic field. This current does indeed oppose the change in the magnetic field, but it does not necessarily stop it. Instead, it slows down the rate of change, allowing the magnetic field to dissipate more slowly.

In the case of a wire with no external current source, the self-inductance will eventually dissipate the energy in the wire as heat. This is because the magnetic field created by the induced current will eventually reach equilibrium and no longer change, resulting in no back emf and a flow of current. This process is known as self-discharge.

So, to answer your question, while it may seem like the wire is just fighting itself and nothing is happening, there is still a dissipation of energy occurring through self-discharge. This is a natural process that occurs in any circuit with self-inductance.

I hope this explanation helps to clarify the concept of self-inductance and the role of back emf in a wire.