Another noob physics question

[Davros]

Imagine you have a device connected to a battery with wires
like so


I'll get this out of the way first, no I cant come and work for your company as an artist

back to the question
Obviously the current flows through the wires to the device powering it

If you measure an electron at point A and measure it again at point B how has it changed and if it hasnt where did the power come from

 

[AlNom]

B is at a lower electric potential.

edit:

Battery has an electric potential, say 1.5V. When you complete the circuit, some rate of electrons flow (current) depending on the resistance of the device (there's also the battery's internal resistance, but we can ignore that for the example). Electric potential of the battery decreases over time as the device uses up the potential energy. Eventually, the voltage supply is insufficient for the device to operate normally.

 

[Davros]

B is at a lower electric potential.

Can you explain that afaik an electron normally has a charge of 1 electron volt
does the electron at B have less than that ?

 

[pcchen]

A more detailed explanation:

Let's talk about electric current in metal wires first (the most common case). The outer most electrons in a metal atom are rather "loose," and in a solid metal, they generally move around more or less freely, jumping from one atom to another. Normally, they move in random directions. However, if there's an electric potential (such as a electromagnetic field), it will force those electrons to move in one direction, thus creating an electric current. It's not unlike a water pipe. Even water in a leveled water pipe flows if you pour water from one end, as the water molecules push other water molecules forwards.

So the key point of creating an electric current is to create an electric potential. A changing electromagnetic field is one way, which is how an electric generator generates electricity. In the case of chemical batteries, the electric potential is created by chemical process. For example, in a traditional "lemon battery," two metal pieces are inserted into a lemon to generate electricity. One metal piece is zine, which oxidizes in acid so it loses some electrons. Another metal piece is copper, where protons capture those electrons to form molecular hydrogen, thus creation an electric potential (as the electrons flow from zinc to copper). When most of the surface of zinc piece is oxidized (or when there's no enough acid in the battery), it can't oxidize anymore so the flow of electrons eventually stops. That's when the battery is "dead."

Can you explain that afaik an electron normally has a charge of 1 electron volt
does the electron at B have less than that ?

The electric charge of an electron never changes. It's approximately 1.6x10^-19 C. An eV (electronvolt) is an unit of energy, not electric charge. An electron gains 1 eV energy when in 1 volt electric potential.

 

[Davros]

Thats a great examination pcchen, but not quite what i'm after
I'll try to explain better
a device needs energy to function, and it must be getting this energy from the electrons, so the electrons at point B must have less energy than the ones at point A
we know that e=mc2 so are the electrons at point b lighter ? do they spin slower ? do they move slower ?

 

[AlNom]

The energy is from the EMF generated by the transfer of electrons.

 

[Grall]

As I understand it, and from the question you ask, nothing really changes about the electrons per se pre- and post-device. Instead, the circuit as a whole changes when you connect a device, or devices to it. The electrons don't get "spent" just by passing through the device, instead you spend the BATTERY, pushing electrons through the device...

Well, that's my layperson's understanding of it anyway.

 

[Davros]

I looked into emf and it appears to be part of the answer.
I did some searching and as b3d readers who read my destroying of XXX's theory that spinning produces anti gravity
http://forum.beyond3d.com/showthread.php?t=58132&highlight=deductive&page=2
a thesis that puts me side by side with the great minds of physics
Newton, Einstein, Dr Bunsen Honeydew
I am indeed the master of deductive reasoning

It appears to be the transfer of momentum from the electrons (via an exchange of virtual force carrier particles in quantum mechanics)

 

[Mendel]

My super layman analogy is as follows: that battery is a pump and device is a waterwheel...
Obviously water runs through the waterwheel, turning it.(rotating? revolving? sorry my nonenglishness is failing me to find the correct word)
If you measure a water particle at point A and measure it again at point B, how has it changed?


To me the question is irrelevant as the power comes from the pump (battery), not from the water particle (electron). I know it maybe somewhat flawed comparison but the big picture should be pretty much the same...

 

[Davros]

that is the answer in a way Mendel
If the device in question is a lightbulb it makes it easier to think about

 

[Gubbi]

As Mendel says, think of the electricity as water flowing downwards.

Current flow, measured in amperes, then equates to water flow (ie. volume).
Electric potential, measured in volt, equates to the height the water.

Cheers

 

[liolio]

The waterfall comparison is good the funny thing is that "electricity" actually moving electrons would be moving from the ground to the top of the waterfall. Still they are negative charge and we measure a intensity as a positive value so intensity goes like a waterfall but there are no moving positive charges.

The most easy mental representation for me was to consider electrons, they move in the proper way accordingly with the U (vector), then it's just a matter to consider intensity (positive charge) moving in the opposite direction as electrons (/and up the waterfall).

 

[Mize]

It's not an electron, it's an electron in a potential field. Like a rock (or water) in a gravitational field...the closer it gets to (the) ground, the less potential energy it has.

 

[liolio]

I'm not sure about what is your point?
I'm just saying that i (which is the arrows on the drawing) is in the opposite direction of the actual electrons flow. U(vector) is indeed a 1d field (weird) a difference in potential point, when you represent U(as vector) it points to the highest potential to the lower, electrons move in that direction (defined by the difference in potential) but i (intensity as a vector) goes in the opposite direction.
In the drawing above if one put the generator on the left, the direction of if the "device" in on the right will be downward, whereas the direction of U is upward.
I'm not sure if 'I'm clear huge vocabulary lacking here

 

[Mize]

What I wrote wasn't directed at you liolio. We have Ben Franklin to thank for electrons running the opposite direction as current - he assumed the charge carriers were positive.

 

[RudeCurve]

*cough*

Conventional Current Flow vs Electron Flow

http://www.rare-earth-magnets.com/t-conventional-vs-electron-flow.aspx

I remember learning this while taking Circuit Analysis class...

You will find conventional flow notation followed by most electrical engineers, and illustrated in most engineering textbooks. Electron flow is most often seen in introductory textbooks (this one included) and in the writings of professional scientists, especially solid-state physicists who are concerned with the actual motion of electrons in substances. These preferences are cultural, in the sense that certain groups of people have found it advantageous to envision electric current motion in certain ways. Being that most analyses of electric circuits do not depend on a technically accurate depiction of charge flow, the choice between conventional flow notation and electron flow notation is arbitrary . . . almost.

As one might guess, polarized device symbols typically contain an arrow within them, somewhere, to designate a preferred or exclusive direction of current. This is where the competing notations of conventional and electron flow really matter. Because engineers from long ago have settled on conventional flow as their "culture's" standard notation, and because engineers are the same people who invent electrical devices and the symbols representing them, the arrows used in these devices' symbols all point in the direction of conventional flow, not electron flow. That is to say, all of these devices' symbols have arrow marks that point against the actual flow of electrons through them.

As to the OP's question the answer is called Potential Difference which is just another term for Potential Energy but measured in Volts. The higher the PD the higher the V the more pressure pushing the current through the wire.

Power = Current x Voltage

If you had two vertical columns of water one with a height of 3ft the other with a height of 6ft, the latter has a higher Potential Difference ie 6ft vs 3ft so the bucket at 6ft has higher water pressure (Volts). Now if the colums of water had different diameters you would add in R which is resistance to current flow.

Volts = Current x Resistance

In other words the "Power" comes from current and voltage or the tendency for electrons to want to move from one point to another when you have a PD "voltage" source in a closed loop.

http://www.physicsclassroom.com/class/circuits/u9l1c.cfm

http://en.wikipedia.org/wiki/Voltage

 

[Davros]

So are electrons negative just because once upon a time some bloke decided to label them as such
It seems counter intuitive if you discovered something carrying a charge you would automatically think it was positive

edit: my google-fu found this explanation

Benjamin Franklin decided there was just one kind of electrical fluid in nature. He opined that wool rubbing wax took electricity away from the wax. The wool ended up with a surplus of electricity and the wax ended up with a deficit of electricity. Therefore, he described the surplus as + and the deficit as -, in analogy to credits and debits of money. This somehow became the usual designation.

The choice became questionable in the nineteenth century. In electrolysis experiments with charged electrodes in beakers of metal salt solutions, metal would deposit on the - electrodes but not on the +. Odd that the deficit electrical part would get more (interesting) activity than the surplus electrical part. This was resolved by Faraday (I think) proposing that metal atoms already have surplus electricity and naturally migrate to the - electrode, being mobile in the solution. He called charged atoms "ions". He found that the quantity of deposited metal could be predicted accurately by current times time.

Later in the nineteenth century, cathode rays were produced and studied assiduously. If the cathode (- terminal) of a cathode ray tube is heated, then cathode rays are produced (a glow occurs). If the anode (+ terminal) is heated instead, this doesn't work. By this time probably nobody cared about which ought to be called + and which ought to be called -. There are cations (+ charged) and there are anions (- charged). The important thing is that the product Q1Q2 is positive when the charges are both + or both - (which means a repulsive force) and the product is negative when the charges are +- or -+ (which means an attractive force).

It must have also set people back in their chairs when Rutherford, Geiger and Marsden in 1911 showed the electrical charge distribution within the space of atoms. Almost all of the space is where the - charged electrons dwell*. All of the + charge (and also the main part of the atomic mass) is concentrated into a very tiny part of of the atomic space, what we call the "nucleus".

*A LITTLE CORRECTION: They thought that some electrons were in the nucleus too. The neutron had not been conceived yet.

 

[AcceleratorX]

Well, I'd like to think of it as having something to do with electromagnetism. The "other end" of the battery is attracting the electron due to a strong electro-magnetic force. Thus, it moves towards it, losing kinetic energy as it works against the system. As soon as kinetic energy is lost, potential energy is gained.

And this potential energy, IMO, is the real electric potential, even though it would be negative from an engineer's point of view due to sign conventions. However you do it, you'll end up the same way in the circuit, though the differences of analysis between and engineer and a physicist are interesting to say the least when it comes to circuits.....

Also note: Total energy=kinetic energy+potential energy. At any point of the circuit, the total energy of the electron will remain the same (not accounting for losses due to surroundings etc.).