Understanding Voltage: How Potentials Differ & Flow

[CuriousBanker]

The concepts of current and voltage are not difficult for me to understand. What I am having difficulty understanding, is what causes it? What causes there to be a potential difference so that when I plug my toaster in, electricity flows through it? How is there constantly a potential difference across my toaster?

 

[BvU]

You have the Lorentz force as source of emf, and in the Maxwell equations there is another (Faraday's law of induction) . I concede that they are not root causes but descriptions of behaviour. But they are at the basis of the work that is done to run your toaster.

 

[Baluncore]

Asking what causes voltage is like asking what causes height.
It takes energy to lift mass up a height, against the attraction of gravity.
Likewise, it takes energy to lift an electron up a voltage, against the attraction of an opposite charge.
When you allow the mass or charge to fall back, it releases the stored potential energy.

 

[Dale]

Summary:: What causes the EMF to push the current through the wire of the appliances at home?

What causes there to be a potential difference so that when I plug my toaster in, electricity flows through it? How is there constantly a potential difference across my toaster?

On the other end of the wires is a very large generator which uses some mechanical force to push a wire through a strong magnetic field. That mechanical force can come from any number of sources: burning fossil fuels in a heat engine, wind, flowing water, a steam turbine, etc. But the main thing is that the mechanical force pushes the wire through a magnetic field which by Faraday’s law produces the voltage across your toaster.

 

[PeroK]

Summary:: What causes the EMF to push the current through the wire of the appliances at home?

The concepts of current and voltage are not difficult for me to understand. What I am having difficulty understanding, is what causes it? What causes there to be a potential difference so that when I plug my toaster in, electricity flows through it? How is there constantly a potential difference across my toaster?

There must be lots on line explaining this. Try this, for example:

http://thecircuitdetective.com/bkgrd.php#sys"

 

[vanhees71]

On the other end of the wires is a very large generator which uses some mechanical force to push a wire through a strong magnetic field. That mechanical force can come from any number of sources: burning fossil fuels in a heat engine, wind, flowing water, a steam turbine, etc. But the main thing is that the mechanical force pushes the wire through a magnetic field which by Faraday’s law produces the voltage across your toaster.

I'm not sure about the conventions, but I'd be careful to call this particular technically very important example for providing electromagnetic energy "voltage". I'd reserve "voltage" only to magnetostatic situations, where $\vec{E}=-\vec{\nabla} \Phi$, i.e., where $\vec{\nabla} \times \vec{E}=0$.

A usual generator, i.e., moving a coil in a magnetic field, works precisely the way it does, because in this more general case $\vec{E}$ is not conservative, but according to Faraday's Law, which in its local form, $\vec{\nabla} \times \vec{E}=-\partial_t \vec{B}$ (SI units), is one of the fundamental Maxwell equations. Here I'd rather talk about electromotive forces (which is also somewhat unfortunate, because it's an ancient expression, where force doesn't mean force in our modern sense but rather an energy-like quantity).

 

[Dale]

I'd be careful to call this particular technically very important example for providing electromagnetic energy "voltage". I'd reserve "voltage" only to magnetostatic situations

I understand your hesitance, but it is measured by a voltmeter and is in units of volts so I am OK with the terminology. And the OP used the terminology rather interchangeably also.

 

[vanhees71]

Yes, sure, but I have some hard time with one forist in the PM, because he doesn't believe me that what a voltmeter measures are not only potential difference but any kind of electromotive force. That's the reason for my caution. The great trouble with Faraday's Law comes from the many sloppy uses of its integrated form and the negligence of the fact that electrodynamics (i.e., the dynamics of the electromagnetic field and charge-current distributions) is only consistent when treated relativistically, but that latter point is another story.

 

[CuriousBanker]

Asking what causes voltage is like asking what causes height.
It takes energy to lift mass up a height, against the attraction of gravity.
Likewise, it takes energy to lift an electron up a voltage, against the attraction of an opposite charge.
When you allow the mass or charge to fall back, it releases the stored potential energy.

If you asked me what causes humans to be lifted up a height in a skyscraper, I would tell you an elevator. I'm having trouble asking exactly what I mean, but how is there a constant voltage going through my house? Why are there always charges separated so that my appliances work? What causes this?

 

[CuriousBanker]

On the other end of the wires is a very large generator which uses some mechanical force to push a wire through a strong magnetic field. That mechanical force can come from any number of sources: burning fossil fuels in a heat engine, wind, flowing water, a steam turbine, etc. But the main thing is that the mechanical force pushes the wire through a magnetic field which by Faraday’s law produces the voltage across your toaster.

ah right. I learned about this years ago. i feel so foolish for forgetting. thanks

 

[kuruman]

Summary:: What causes the EMF to push the current through the wire of the appliances at home?

The concepts of current and voltage are not difficult for me to understand. What I am having difficulty understanding, is what causes it? What causes there to be a potential difference so that when I plug my toaster in, electricity flows through it? How is there constantly a potential difference across my toaster?

Although your toaster at home runs on electricity produced by generators as previously pointed out, it can also run (in principle) on batteries. Your toaster doesn't care if the voltage across its heating element is maintained by a power plant, a battery or whatever. Batteries involve electrochemical separation of charges that accumulate on the battery terminals. The "voltage" of a battery is the electric potential difference between the terminals that is maintained by the separated charges. You can find out more about this including the answer to "what keeps the current flowing?" if you do a bit of web search. There is tons of stuff out there.