Why electricity flows

Originally posted by PhoenixOD
Either way its the passing of excessive amounts of electrons that makes up the flow of electricity.

In some cases perhaps but not necessarily. In p-type semiconductors it can actually be a shortage of electrons that makes up the flow. These shortages are called "holes".

en.wikipedia.org...

When a doped semiconductor contains excess holes it is called "p-type", and when it contains excess free electrons it is known as "n-type", where p (positive for holes) or n (negative for electrons) is the sign of the charge of the majority mobile charge carriers.

Originally posted by winofiend
How fast is it?

Serious q??!!

How fast is what? There are two different things involved:

1. Electrons- they don't move very fast, in fact they are pretty slow. In an AC circuit with little or no load, they may hardly move at all but just oscillate.
2. Electromagnetic fields- They move at a the speed of light in a vacuum, but a little less than that in non-vacuum conditions like copper conductors. The exact fraction of the speed of light the fields travel at can vary depending on the conductor and the material surrounding the conductor, but 96% the speed of light may be a typical value for an unshielded copper conductor.

en.wikipedia.org...

The word "electricity" refers generally to the movement of electrons (or other charge carriers) through a conductor in the presence of potential and an electric field. The "speed" of this flow has multiple meanings. In everyday electronics, the signals or energy travel quickly, as electromagnetic waves, while the electrons themselves move slowly.

reply to post by intrptr


The root mean square (RMS) value of a alterating current voltage waveform AC voltage is the equivalent DC voltage that produces the same power dissipation in a load. So yes its ok to say light bulbs are powered by DC power.

reply to post by AthlonSavage


Thanks for helping me explore the issue...

www.physicsforums.com...

From comments section:

The designation of what is "high" and what is "low" is actually done by convention. Nature actually doesn't care what we call it. So assigning something to be + or - is also by convention (or in this case, tradition).

Would it help if you imagine positive charges to be globs of water, while negative charges to be air bubbles? The globs of water, such as water drops, will tend to fall to the ground, whereas air bubbles in water will tend to "fall" upwards.

The "energy" comes from the field, where the field does work on both + and - charges.

In physics, electrical current is considered to flow from the positive to the negative pole. This is known as theoretical current or conventional current. If you connect a light bulb to a battery, therefore, the theoretical current flows out of the positive terminal and into the negative terminal. But the electrons, which carry the charge, flow in the opposite direction, from negative to positive. This is the way engineers usually think about current."
Electricity Demystified by Stan Gibilisco

The electrons do move from the negative terminal to the positive terminal, if you're talking about DC current. However, they can't move unless there's a 'hole' to move to. Once they move, the 'hole' has moved to the slot the electron used to occupy. Either way you look at it, a charge has moved. The movement of the 'holes' is what you normally track, since that's the actual electrical energy.

With an AC signal, the electrons don't even move from the negative to the positive. They just move back and forth.

The best way to think of it is the motion and energy transferred by a wave. For example, sound requires air or some other material in order to be transmitted as a wave. It's the movement of the wave you're interested in, not the movement of the air molecules.

reply to post by AthlonSavage


So if it's so like water, why doesn't it fall out of wall sockets if nothing's plugged in?

Originally posted by nerbot
reply to post by AthlonSavage

 

So if it's so like water, why doesn't it fall out of wall sockets if nothing's plugged in?

LOL, surface tension.

Ok, so i know nothing about electricity. I still know about smart aleck replies.

reply to post by nerbot

So if it's so like water, why doesn't it fall out of wall sockets if nothing's plugged in?

This is good question. The easiest way to answer it is to say the output of the wall socket is seeing a very large resistance that prevents the electric current from flowing out.

Another way of looking at it is to say the air around socket face is a good insulator. The voltage that is required to break down air at normal room temperature and pressure is about 3000Volts per millmetre. At that point the air will begin to breakdown and become partially conductive. This is why in the design of electrical equipment installations a physical separation distances must be adhered to. For example there will be minimum physical separation air gap distance between the electrical circuit and the equipment enclosure metal frame. Air gap or another term voltage creepage distances are defined in engineering standards.

Ok. You have a voltage and a good current available. The electrons flow through a radiant (Bar) heater. Where does the heat come from. Consider before you reply, the electrons are not used up, they have not lost speed, they still measure 1eV on either side of the bar element. From every measurement we can make, nothing has changed.

P

reply to post by pheonix358


The heating effect in the resistive element is caused by the interaction of the moving electrons and the atoms which make up the resistive element. Some of the energy contained in the motion of the electron is given up to the atoms in the material. The atoms in the material absorb this interaction which causes them to vibrate. The vibration of the atoms produces the heat.

The 1eV across the resistive element will comply with the relationship V = I x R. The electrons are not used up or consumed, they only give up some motional energy due to kinetic interaction with atoms in the material. The thing to keep in mind is that energy cannot be created or destroyed in natured but only transformed from one form of energy to another. In this case we are seeing some of the motional energy of the electrons transferred and absored by the material itself, and the energy transformed is heat output.

reply to post by AthlonSavage


Sorry but I would dispute that. The electrons are still traveling at the same speed as they come out as when they went in. It is the same for any circuit. A transmitter does not send every second or third electron up the aerial. LOL.

I mean no disrespect, but the science you have been taught has never answered these questions to my satisfaction.

P

Originally posted by pheonix358
reply to post by AthlonSavage

 

Sorry but I would dispute that. The electrons are still traveling at the same speed as they come out as when they went in. It is the same for any circuit. A transmitter does not send every second or third electron up the aerial. LOL.

I mean no disrespect, but the science you have been taught has never answered these questions to my satisfaction.

P

Weird, because this is really basic stuff. The electrons are slowed down due to material resistance. To maintain a constant speed/current there has to be an external potential, the voltage difference measured between in and out.

This is analogous to viscous friction/drag.

reply to post by pheonix358

Sorry but I would dispute that. The electrons are still traveling at the same speed as they come out as when they went in. It is the same for any circuit. A transmitter does not send every second or third electron up the aerial. LOL.

I mean no disrespect, but the science you have been taught has never answered these questions to my satisfaction.

P

If a voltage source is placed in parallel to a resistor element, the voltage across the resistor will be the same as the source. The quantity of electrons flowing in and out is a measure of the rate at which charge flows past a given point in an electric circuit. . The rate and the in and out the resistor is the same because the voltage drop across a resistor circuit is equal to the constant DC voltage source which is connected across it. The Electric current is measured in Coulombs per second which is named Amperes

Originally posted by moebius

Originally posted by pheonix358
reply to post by AthlonSavage

 

Sorry but I would dispute that. The electrons are still traveling at the same speed as they come out as when they went in. It is the same for any circuit. A transmitter does not send every second or third electron up the aerial. LOL.

I mean no disrespect, but the science you have been taught has never answered these questions to my satisfaction.

P

Yes you understand it well.


Weird, because this is really basic stuff. The electrons are slowed down due to material resistance. To maintain a constant speed/current there has to be an external potential, the voltage difference measured between in and out.

This is analogous to viscous friction/drag.

Greetings. I applaud your effort and deep interest in natural sciences. Thank you.

At the same time, I think your exposition is flawed. See comments below.

Originally posted by AthlonSavage
Voltage is an electrical form of pressure and to understand this concept in the easiest of way is done by
considering its analogy to a fluid system. A simple form of fluid system is found in a rainwater tank. The Pressure inside the tank is greater than the ambient atmospheric pressure surrounding the tank. To release water from the tank into the external environment is controlled by opening a tap on the tank.

Here's the thing: pressure (as in hydrodynamics) is caused by the medium itself, its constituents. However, a charge can move under the influence of a field, produced externally by sources located at a distance -- sometimes quite large. Your model breaks way too soon when we start looking at electricity. You can't explain the transformer operation, for example.

The flow of water in this manner is analogous to the flow of current. The current flow is commonly referred in everyday terms as electricity.

The flow of electricity is an effect caused by electrical pressure of voltage. To increase the magnitude effect of the flow in electricity (electric current) requires increasing the voltage pressure.

Your definition of "magnitude of flow" is imprecise. For example, does it include the speed at which the charges are moving? Or just the current? Unclear. If it's about velocity, a small potential can obviously accelerate the charges to a higher speed than a high potential, depending on the system.

Therefore think of Volts as electrical pressure.

I can't, it's just wrong.

To explain Resistance I will go back to the analogy to a fluid system and a rainwater tank. Imagine now that a hose is connected to the outlet tap on the tank. When the tap opened the water will flow from the tank via the tap and through the hose. The hose itself is physical a Resistance element in the flow path of the fluid; in that it slows down the rate of fluids flow from the tap. Without the hose connected to the tap the water fluid flows out of the tap at a faster rate compared to it the hose is connected.

True, but it makes you wonder what the resistance of the tap itself is due to... Which again hurts the analogy. The electron flow doesn't really have viscosity in most cases (I may be wrong in which case correct me).

A hot iron is the best example as because altering the temperature control has the actual result of altering the resistance in the circuit.

This is simply wrong. Temperature control in hot iron (both used for hair, and the pressing iron) is achieved by a thermostat, which is a form of pulse control, i.e. the current is pulsed to keep the temps as the desired level. I thought you'd figure this out because passing a current that big through a variable resistor would cause energy dissipation in that element comparable to the iron itself, or even larger.

reply to post by buddhasystem

Poiseuille's law for fluids:
volume flow rate = (pressure in - pressure out) / flow resistance

Ohm's law for electric circuits:
current = (voltage in - voltage out) / electrical resistance

This is called water circuit analogy.

Originally posted by moebius
reply to post by buddhasystem

 

Poiseuille's law for fluids:
volume flow rate = (pressure in - pressure out) / flow resistance

Ohm's law for electric circuits:
current = (voltage in - voltage out) / electrical resistance

This is called water circuit analogy.

I first did an experiment using the Poiseuille law when I was 15, and since then I remember that the viscosity is in that equation. That's important, I already mentioned that in my previous post. There is no viscosity in the flow of electrons, so the analogy is quite superficial. The physics is different. I know one can construct an equivalent of resistance out of the parameters like viscosity, diameter and length of the pipe etc, but that's just superficial afaimc. So what's left is just a linear dependence, which is quite common in nature and no illuminating at all. I'm not even talking about the limits of Poiseuille law.

If you guys who are asking questions, ever need to figure out wattage (P) for a given device, simply mulitply your amperage (I) by your voltage.

Everyone loves P=IE

Electrical theory is yummy too


Posted Via ATS Mobile: m.abovetopsecret.com

Originally posted by spinalremain
If you guys who are asking questions, ever need to figure out wattage (P) for a given device, simply mulitply your amperage (I) by your voltage.

As the OP correctly pointed out, this doesn't quite work this way for AC.

reply to post by buddhasystem

[edit]: Nevermind, you were talking about inductive/capacitive/efficiency, I´m going into the wrong direction in
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hm if you think the generator as a turbine pushing the water in different directions with 50/60 Hz, you can explain the heating the same way as with electron just in a larger scale. the water molecules (=electrons) will heat the pipe because energy is lost when colliding at the walls. This must be compensated by the pump. They will draw more energy from their source of power.

Tiny dents inside the pipe -> greater resistance -> energy converted by resistance -> heat.
Really high pressure and no resistance -> fast flow -> almost shortcut -> heat.

Originally posted by StareDad
hm if you think the generator as a turbine pushing the water in different directions with 50/60 Hz, you can explain the heating the same way as with electron just in a larger scale. the water molecules (=electrons) will heat the pipe because energy is lost when colliding at the walls.

This is wrong. Energy dissipation happens in bulk fluid as well on the boundary, and the bulk loss can be larger (and I think usually is in the laminar flow case). Again, it's not the matter of the pipe itself.

Viscous fluids will dissipate energy within themselves. This is another factor that makes the electron analogy unsuitable.