speed of electricity

[bwanaaa]

It seems almost a reflex, when you ask someone 'what is the speed of electricity' they say 'the speed of light'. Why?

photons are not electrons. they travel in different media. photons travel slower through liquids and even slower through solids.

Are there any experiments that ascertain the speed of electricity?

is it possible to dramatically SLOW DOWN the speed of electricity?

I'd like to pour it out of a glass.

 

[CTho9305]

Electric fields => c. electrons => slowwwww.

 

[zephyrprime]

As I recall, electricity does travel at near the speed of light. But the electrons do not. I recall that the electrons in a automotive electrical system only travel a few centimeters/second.

 

[Geniere]

Bwanaaa, the speed of a photon is always = C. It doesn?t matter if it is traveling through a brick of lead or a vacuum, it always moves at C. The apparent slower propagation through a medium such as glass is because a photon interacts with electrons in the glass. A photon will be absorbed by an electron, and acquire higher energy. Almost instantaneously, the electron re-emits a different photon. The additional time required for this process of absorption and re-emission accounts for the observed decrease in speed.

Experiments determining speed of electrons were done over a hundred years ago and define the ampere which is a flow of charge i.e. electrons per second.

An individual electron in a circuit does not move very fast, it may go in the wrong direction, but the there is an average slow drift of electrons towards the positive charge.
What does move very quickly is the EM field that is responsible for the seeming high speed of electrons when turning on a light.

It is not possible to answer your question re: speed of electricity as electricity has no physical meaning. If you mean the speed of an electron, that can be answered. Any particle that has mass such as an electron can have zero speed. All particles that have zero mass, such as a photon, always move at the speed of light (C).

 

[PowerEngineer]

While it's certainly common to talk about electricity in terms of just the alternating voltages and currents, don't forget that that these set up alternating electric and magnetic fields. In fact, you can consider the conductors to be just a wave guide for these electromagnetic fields.

When we talk about the speed of light, it seems to me that we normally mean the speed of light in a vacuum. The speed of light through anything other than a vaccum is somewhat less depending on the characteristics of the materials involved.

So what I'm saying is that because electricity is electromagnetic waves (just like visible light), it does travel at the speed of light; however, that speed is less than the speed of light through a vacuum.

 

[Shalmanese]

An EM field in a copper wire is roughly 2/3 the speed of light. This is important to know when your sending signals down a wire. The speed on optical fibre is roughly 99% the speed of light.

 

[bwanaaa]

thank you for your replies.

Ah yes. I actually remember knowing this once, ages ago. Amazing feeling, remembering knowledge as if it were a friend, a person or a thing. Yes, in the context of physical chemistry and the velocity of ions through a solution. As I further recall, in a metal, electrons constitute a 'cloud'. As electromotive force is applied to one, its electrostatic force repels the one in front of it, nudges it closer to the electron in front of it, repelling that one. The chain reaction is similar to tugging on the end of a chain. though the chain moves slowly across the floor, the transmission of force through the links of the chain is 'instantaneous'. but it really isnt instantaneous. the first link pulls on the second link 'long' before the penultimate link pulls on the last one. in fact, doesnt the transmission of force through the chain travel at the speed of light? after all, the force is just the repulsion of electrons in adjacent atoms. the inference that 'electricity travels at the speed of light' derives therefore from the fact that we presume that the em field travels at that speed. But does it?

a photon is not an em field. as i recall, it is a disturbance in an em field. photons can travel through an absolute vacuum. there are no photons invloved in the transmission of electricity. my guess is that the transmission of voltage is slower than the speed of light because of the 'squishiness' of the electron cloud in the metal. someone told me about an analogy to a slinky. imagine the velocity of waves through a slinky , now imagine the slinky spring stiffer-the waves travel faster. this might predict the velocity of electricity in different metals would be different. any measurements here?

 

[uart]

Hi bwanaaa, a good analogy to the difference between the speed of the E-M wave which carriers the energy (or signal) and the speed of the individual charge carriers would be to compare it with pumping water through a pipe. The bulk speed the water in the pipe may be relatively slow but if we abruptly change the speed of the pump then the induced pressure wave will travel at the speed of sound in the media - several km per second for water.

The speed of the actual electrons (or charge carrier drift velocity) depends on the ratio of the current density to that of the charge carrier density. Higher current denity to carrier density ratios give higher drift velocities and lower current density to carrier density ratios give lower drift velocities.

In most metallic conductors the carrier density is extremely high, so that from most usable curret densities the drift velocity is seldom more than a few mm per second, and often even less. Semiconductors on the other hand frequently have carrier densities that are up to 10 orders of magnetude (10^10) less than metals and so the drift velocity can be very much higher, though still less than c of course

 

[bwanaaa]

hahaha, the speed of sound!!! that'll be another whole dissertation-why pressure waves travel through water att the speed of sound, not the speed of light.

 

[Lonyo]

Originally posted by: Shalmanese
An EM field in a copper wire is roughly 2/3 the speed of light. This is important to know when your sending signals down a wire. The speed on optical fibre is roughly 99% the speed of light.

In optical fibres, it's light that's sent down them, so it must travel at the speed of light (although because it's not a straight line down the cable, it can't quite reach 100% of the speed of light). The electrical signals are changed into light pulses, then changed back at the other end.

 

[glugglug]

Is it possible that the reason light is slower when not traveling through a vacuum is because it is not travelling in a straight line? (or rather, not radiating out in a perfect sphere...). The gravitational field near an atomic nucleus is extremely strong. Perhaps the extra time to travel through glass or other materials is from the amount of redirection that occurs near each atom before the light finally makes it out the other side, which just appears to pass straight through and come out at one point on the other side because of the law of averages?

 

[Geniere]

Light always, always, always travels at exactly the speed of light. It never varies. It always propagates at exactly C. Every measurement made in every imaginable circumstance yields the same result i.e., light propagates at exactly C. It might be easier to understand this if one realizes that light always travels in a vacuum. It is impossible for light not to travel in a vacuum. If it is passing through lead it moves at the speed of light until an electron absorbs it. Remember the voids between atoms even in a dense substance are vacuums. A photon having sufficient energy, such as x-rays, may seem to pass through but it is not the same photon that entered. The exit photon is the result of many absorptions and re-emissions.

 

[imgod2u]

Erm, no, c is the speed of light in a *vacuum*. You can certainly slow light down. Put stuff in its way. Atoms absorb photons all the time (effectively bringing their speed down to 0) and release electrons (electrons hit by photons gain enough energy to break its bond).
The speed of light, however, does not vary with the *frame of reference*. That is, if you were traveling at 5000 km/s away from someone else and you shot a beam of light forward, both you and the person you're moving away from will see the photon go at 300,000 km/s.

 

[Geniere]

Quote: ?Erm, no, c is the speed of light in a *vacuum*. You can certainly slow light down. Put stuff in its way. Atoms absorb photons all the time (effectively bringing their speed down to 0) and release electrons (electrons hit by photons gain enough energy to break its bond).?

Imgod2u:

That statement is incorrect. When a photon interacts with an atom it is either absorbed or scattered. If it is scattered, it can impart some of its energy to the atom. There are many types of scattering events, the most common of which for lower energy photons is called Compton scattering. The effect on the photon is to reduce its energy (increase its wave length). The photon continues to propagate at the speed of light albeit at a lower energy. An atom can absorb the photon. If it has very high energy, say about 15mev, it may be absorbed by the nucleus. The interaction with the nucleus because of the high energy required is much less likely than for the photon to be absorbed by an electron orbiting the nucleus. This orbiting electron can occupy various shells depending on the electrons energy. QED tells us that an electron can only absorb a photon having a specific energy. If the electron interacts with a photon of the correct energy, it will absorb it. The photon is annihilated, it ceases to exist, it is kaput. The speed of the photon is NOT ?effectively brought down to 0?, the photon, as I stated, is annihilated. The electron having acquired the photon?s energy then moves to higher energy shell. Almost instantaneously, it falls back to a lower energy shell. To fall back it must emit a photon to shed its excess energy. This newly created photon then propagates at the speed of light. Never does a photon propagate at a speed different than C.

AS far as the electron breaking its ?bond?, that is a possible occurrence. It is more likely that the orbital electron will simply be moved to a higher energy shell. If the incident photon has sufficient energy, it may impart enough energy to the electron (a scattering event), that the electron is freed from its atomic association. The atom then has a net positive charge and becomes an ion. This process is called ionizing radiation. Some uses of ionizing radiation are for cancer therapy and food sterilization

One should not adhere to physics principles generally taught in grades K-12, which may seem to support your concepts. Many HS physics teachers have provided this erroneous information on web sites. Don't confuse wave front propagation with the speed of a photon. A wave front can be the result of the total summation of all photon interactions and as such, wave front propagation can be less than C. The speed of wave front propagation accounts for the seeming slowing of the speed of light in a fiber optic cable and in an electrical circuit.

Quote: ?The speed of light, however, does not vary with the *frame of reference*. That is, if you were traveling at 5000 km/s away from someone else and you shot a beam of light forward, both you and the person you're moving a way from will see the photon go at 300,000?

This statement is correct as far as it goes, but the observer will see light of a different color i.e., it will appear to be ?red shifted?, have lower energy. If you were moving toward the observer, it will appear to be ?blue shifted?, have higher energy. You will not note any energy change.

 

[bwanaaa]

light that we observe is a macroscopic event-the statistical average of countless photons. Although photons never slow down, the speed of light can be seen to be less than c if the photons are interfered with-bent, absorbed and emitted, etc. A similar paradox is illustrated by the concept of light reflection. We all know the angle of reflection is equal to the angle of incidence. is it because photons are billiard balls? Feynemann however had something quite different to say about this. When he looked at the behavior of individual photons his theory of QED poses a very different behavior of indiividual photons but the 'average of those behaviors' appears as the reflection law we know.

 

[PowerEngineer]

Slow Light

Light moves with speed c in a vacuum. But light can move with a speed less than c, when it passes through some material. The table shows the speed of light when it goes through glass, water, and air. Note that in this table the speed of light in each material is given as a decimal times the speed of light in a vacuum.

Material Speed of light in this material

Glass .66c
Water .75c
Air .9997c

(from PhysicsCentral)

 

[Geniere]

Power Engineer:

Please be aware of the difference between wave front propagation and the speed of the individual photons contributing to the wave front. Your table is correct insofar as the speed of the wave front. However each photon does travel at exactly C.

As you know, the only physical force that can alter the speed of a photons is the force of gravity. Gravity from a massive object such as a star can bend light or curve space making the light appear to bend. The gravitational force of a single atom is so small that it has no effect on a photon. I've described in my previous post two possible interactions of a photon with an atom, there are other possible interactions, but while some alter the frequency (energy) of a photon, none alter its speed

 

[Geniere]

Bwanna, your very basic questions in the original are in stark contrast to your last post. That post indicates a level of understanding that makes me wonder why you asked the questions in the first place.

Feynman's book, QED is excellant reading for anyone interested in light and electron phenonema. In that book Feyman assigns vectors of a length porportional to the probability of an event. With that basic premise, he explains the processes quickly and clearly without the drudgery of complex math. It's a small book, when you finish it, you will wish it were longer.

 

[PowerEngineer]

Geniere:

As my previous posts indicate, my thinking goes more to the light's wave nature than its particle (i.e. photon) nature. Grappling with this duality makes clear thinking difficult (for me) and clear communication even more difficult.

If I understand you correctly, you are saying that an individual photon always travels at the speed of light (as measured in a vacuum and putting aside the gravitational effects). To the extent that photons traveling through a material interact with that material through absorption and reemission, then the time it takes for a photon to pass through the material is lengthened by the time these absorptions and reemissions take. The result is that it takes longer for photons (i.e light) to travel through the material (I realize that the photons entering the material are not the same as the ones leaving it), and therefore the photons seem to be moving at a slower speed. I believe this is what you mean by slower wave front propagation.

I've done a little more quick reading and have a couple of additional links:

Ruby Slows Light at Room Temperature

Is It Possible To Slow Light Down?

So I agree with you that photons always travel at the speed of light as measured in a vacuum. The speed at which light (i.e. the swarm of photons) propagates through a material can be much slower than the speed of light as measured in a vacuum. Shifting to my more comfortable wave language, that's also true for all electromagnetic radiation, including our 60 Hz electricity, although I don't think Bwanaaa will be pouring it out of a glass anytime soon.

:beer:

 

[rjain]

As before, you need to distinguish between the speed of light and the speed of a photon. Also, the speed of the propagation of EM impulse can be different (and can be different for the direction vs. the magnitude).

The speed of a photon is c, as far as we know.

The speed of light is the speed of a group of photons interfering with each other. The front of that waveform can propagate at no more than c, but the peak can propagate at any of a variety of speeds. That is the "speed of light" that is affected by refraction. In particular, the bending of the light wave is a result of this interference among the photons.

The next one is my conjecture. The speed of the propagation of the magnitude of the EM impulse would be the speed of propagation of the photons involved. The speed of propagation of the direction of the EM impulse would be the speed of propagation of the decoherence, which necessarily must be "infinite" in that it propagates from source to sink in 0 time in Lorenzian Relativity. Note that in General Relativity as well as Non-Quantum Electrodynamics, we propagate the field strength at infinite speed.

 

[TTM77]

Light and Electricity are two different things. I'm sure everyone agree on that.

Lets talk about light first.
==================
Light is proton and it has frequency which is called wavelength. The thing that answer most of your questions is a glass triangle with a beam of white light stricking it and it created the rainbow. The question is how does that rainbow got created? Imagine a fast car making the turn with distance X and a slow car making the same turn with same distance X. The slow car will make the turn better while the fast car hit the curve. So the light with slow wavelength will make better turn when it hit that triangle glass. The fast wavenlength won't be able to turn as fast and it got redirected at a different location. Now there is a crytical angle, if the angle get less then that then the light will bounce right off (call deflect not reflect).

Can we change the light direction? Yes, we can use deflect and reflect and gravity to change the direction of light.
Can we slow light down? Yes, the medium is the key but once it pass that medium it will go back to it's orginal speed.

Now this question is questionable:
How does light travel through the medium? From what I understand light travel pass the molecular that make up that medium but it does get affect by the medium because the medium has it's own energy to slow down the light. When the light hit the molecular that's when it excite that molecular and create warmth.

Electricity
=======
Electricity is electron. The magnetic field strip the most outter electron to pass to the next nuclearious. So basically the generator pushes the electron to one side which get push onto the wire and since the electron want to go back to the nuclear that have less electron they would have to travel through all those wires to get back because the generator keep pushing them one way. The generator and the motor are very similar. Imagine the generator is built to push the electron while the motor built to get push by the electron. since the electron have to jump from one nuclearious to the next, it will be slower then light.

 

[rjain]

Light is not a proton, TTM77.
It is a wave of photons. The frequency and wavelength of a wave are related by the wave's speed. They are not the same thing. Its speed is 3x10^10 m/s (relative to the local gravity field in Lorentzian Relativity).

Light travels through a medium by simply existing. It doesn't need any molecules. Photons are first-class citizens of the particle zoo, except that they don't have mass like some other particles. It is the interactions with the other (electrically and, to a lesser extent, weakly and, to a lesser extent, gravitationally charged) particles that causes the photons to be "sidetracked" into interactions with those other particles. Sometimes those particles will have other interactions that prevent another photon from being re-emitted along the same path and at the same frequency as the one that was absorbed. However, usually there is some small delay or phase change that distorts the waveform, causing it to bend.

Electricity is not an electron either. It's actually also a wave of photons, but one of force-bearing "virtual" photons, according to the contemporary nomenclature. (My theory of decoherence would obviate the need for real vs. virtual particle distinctions.) The speed of electricity is not the speed of the individual electrons. It is the speed of the wave, which is slowed down by the fact that electrons are massive and are slowed further by interactions with nuclei, as you explained.

 

[Geniere]

Power Engineer:

I wish I could communicate as clearly as you! It seems were in agreement.

After reading Rain?s posts, your post, and other?s, it suddenly dawned on me that a lot of people distinguish between light and a photon. Many think of light as a shower of photons, whereas in my mind?s eye light and a photon are identical. Maybe I?m out in left field on that point.

In response to Rjain?s conjecture, I have trouble enough contemplating what a field is, let alone its speed of propagation, but I?ll throw myself to the dogs with this statement. I believe that the instant a field is created; the effect of that field is instantly felt throughout the universe.

 

[PowerEngineer]

Originally posted by: TTM77
Light and Electricity are two different things. I'm sure everyone agree on that.

What we think of as light is a narrow portion of the electromagnetic spectrum. Other portions of the spectrum, both higher and lower, are also electromagnetic radiation and are therefore fundamentally similar. The electrical power systems operating at 50-60 Hz are at the very low end of this spectrum because their alternating voltages and currents set up alternating electric and magnetic fields that are in fact electromagnetic radiation. This means that both light and AC electricity are electromagnetic radiation.

As Geniere and I have discussed, light has complex nature that means it has wave characteristics and particle characteristics at the same time. Which of these models for light you choose to use may depend on what you're trying to do with light. Electricity is somewhat similar, in that we normally choose to think about electricity in terms of voltages, currents, and impedances (and encapsule its inherent electromagnetic properties in capacitance and inductance). However, it can also be treated as an electromagnetic phenominon where the power is carried by the electromagnetic fields and the wires act as wave guides (that must be designed with the right characteristics to generate the fileds required).

 

[TTM77]

Originally posted by: PowerEngineer


What we think of as light is a narrow portion of the electromagnetic spectrum. Other portions of the spectrum, both higher and lower, are also electromagnetic radiation and are therefore fundamentally similar. The electrical power systems operating at 50-60 Hz are at the very low end of this spectrum because their alternating voltages and currents set up alternating electric and magnetic fields that are in fact electromagnetic radiation. This means that both light and AC electricity are electromagnetic radiation.

As Geniere and I have discussed, light has complex nature that means it has wave characteristics and particle characteristics at the same time. Which of these models for light you choose to use may depend on what you're trying to do with light. Electricity is somewhat similar, in that we normally choose to think about electricity in terms of voltages, currents, and impedances (and encapsule its inherent electromagnetic properties in capacitance and inductance). However, it can also be treated as an electromagnetic phenominon where the power is carried by the electromagnetic fields and the wires act as wave guides (that must be designed with the right characteristics to generate the fileds required).

I feel that you are saying using the spectrum frequency to determin the property and I think it is wrong. Everything have frequency. Even the engine in your car has frequency and it measured by RPM. But the engine is not light nor electricity. Everything has it's own critical frequency, if U get it then u will get that thing to excite like Microwave getting water to excite. So you kinda heating the water inside the food.

I admit that I don't really know what exactly light made up. There are two main elements that we sure of is electron and proton. So which one is light? Or is it something else? How does plant use that something else to make glucose? If all lights are the same, why do plants reflect only green?

Other questions, how does the light bulb works? The electricity travel in this thin wire and the wire glow. Why the wire glow? Is it giving off electrons? What is it giving off that make it glow? Must it heat up to glow or can it glow without heating up?

So many questions but so little answer.