# Electromagnetic induction (1 Viewer)

#### NexusRich

##### New Member
I am still struggling to understand the concept of EMF.
So my understanding of EMF is that it will be produced when there is a relative motion between the magnet and the coil, and that this electromotive force is measured in volts.

But I really dont understand how the relative motion creates the EMF in the first place ( i.e. what is going on on the molecular level that produces a 'voltage', and also why is EMF measured in voltage (what does it have to do with the potential difference in terms of particles etc.)

Could someone please explain this, thank you !

#### tito981

##### Active Member
So there is a current carrying wire which produces its own magnetic field. Relative motion between a electromagnet and a wire causes emf, the direction can be calculated through Fleming’s left hand rule, where the index finger is the direction of the magnetic field from the electro magnet and the thumb is the force which is the direction of the relative motion, therefore a current is induced in the direction of the middle finger.

The production of emf is the same thing that creates a resistive force when dropping a bar magnet through a magnetic conducting tube.

The explanation for the molecular level is quite complex even the simple idea of what actually cause a magnetic field from a current carrying wire is not taught nor assessed in the hsc.

#### Qeru

##### Well-Known Member
But I really dont understand how the relative motion creates the EMF in the first place ( i.e. what is going on on the molecular level that produces a 'voltage', and also why is EMF measured in voltage (what does it have to do with the potential difference in terms of particles etc.)

Could someone please explain this, thank you !
This is an excellent video related to your problem of 'satisfication' of learning:
. Simply put Faraday's law states an EMF is produced when a coil experiences a change in flux, any further 'whys' will simply leave you unsatisified as they simply aren't at an HSC level.

#### idkkdi

##### Well-Known Member
So there is a current carrying wire which produces its own magnetic field. Relative motion between a electromagnet and a wire causes emf, the direction can be calculated through Fleming’s left hand rule, where the index finger is the direction of the magnetic field from the electro magnet and the thumb is the force which is the direction of the relative motion, therefore a current is induced in the direction of the middle finger.

The production of emf is the same thing that creates a resistive force when dropping a bar magnet through a magnetic conducting tube.

The explanation for the molecular level is quite complex even the simple idea of what actually cause a magnetic field from a current carrying wire is not taught nor assessed in the hsc.
gang sign hand rule yikes.

use right hand palm rule lol.
I am still struggling to understand the concept of EMF.
So my understanding of EMF is that it will be produced when there is a relative motion between the magnet and the coil, and that this electromotive force is measured in volts.

But I really dont understand how the relative motion creates the EMF in the first place ( i.e. what is going on on the molecular level that produces a 'voltage', and also why is EMF measured in voltage (what does it have to do with the potential difference in terms of particles etc.)

Could someone please explain this, thank you !
electromotive force is just a name for the 'voltage' induced by changing magnetic flux. Only with voltage can you have an induced current. V = IR.

Now, electromotive forces arise from the interaction of magnetic fields.
If magnetic flux per time is changing, the magnetic fields are interacting differently.
Faraday's law is kind of like Newton's 3rd law. Basically if something does something to you, you do something to that thing.
If something does something harder to you, you do something harder to that thing.
As the interaction of magnetic fields changes with changing flux, the coil has to do something. So it gets an induced EMF changing its own magnetic field which does something to the other magnetic field which is changing its magnetic flux and doing something.

P.S.
technically the - sign on faraday's law is lenz's law and faraday just refers to the variation of magnitude.

#### idkkdi

##### Well-Known Member
So there is a current carrying wire which produces its own magnetic field. Relative motion between a electromagnet and a wire causes emf, the direction can be calculated through Fleming’s left hand rule, where the index finger is the direction of the magnetic field from the electro magnet and the thumb is the force which is the direction of the relative motion, therefore a current is induced in the direction of the middle finger.

The production of emf is the same thing that creates a resistive force when dropping a bar magnet through a magnetic conducting tube.

The explanation for the molecular level is quite complex even the simple idea of what actually cause a magnetic field from a current carrying wire is not taught nor assessed in the hsc.
On the molecular level, in metals, the moving electrons generate a current where each individual electron's magnetic field superimposes with each other to generate a net magnetic field.
You could break down the magnetic field interactions into sub-interactions between the external field and the electrons and sum up all these, but that's pointless.

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#### idkkdi

##### Well-Known Member
I am still struggling to understand the concept of EMF.
So my understanding of EMF is that it will be produced when there is a relative motion between the magnet and the coil, and that this electromotive force is measured in volts.

But I really dont understand how the relative motion creates the EMF in the first place ( i.e. what is going on on the molecular level that produces a 'voltage', and also why is EMF measured in voltage (what does it have to do with the potential difference in terms of particles etc.)

Could someone please explain this, thank you !
for why an electric field creates a magnetic field,

you would have to look at mod 7, which basically just recites stuff like Ampere's law and Maxwell's equations, which has maths likely too hard for you to deal with lol.

Another approach is general relativity, considering length contraction, which is probably a yikes as well.