Ask a physicist anything.

[Cabal]

On a more serious note, what is electricity?
I know about the various ways to measure it (amps, volts, current, charge, etc, none of which *are* electricity), but what IS electricity?
I've heard from many (including teachers) that it is the flow of electrons through a conductive medium, but apparently that is not necessarily correct in all cases.
So, asking a physicist....what *is* electricity?

Thanks in advance, since I've found nobody (not a single person online or IRL) who can successfully answer this question to date.

More generally, a flow of charged particles, under the influence of an electric field. Conductive medium isn't exclusive either. Charge in insulators will move...just not necessarily flow.

 

[kangitanka]

How did Young perform the famous double slit experiment, considering that he apparently performed it circa 1801, and the experiment apparently needs a coherent light source?
According to what I've been able to dig up in books, Young didn't actually use a double slit, but rather a thin piece of card dividing the thin beam of (I'm guessing- non-coherent light).

Have you actually seen the famed Double Slit experiment utilizing sunlight, or any other form of projected non-coherent light (IRL)? Or is this explanation of the experiment just incorrect?
Or is it correct, but I'm misunderstanding something?

Thanks in advance

 

[Cabal]

How did Young perform the famous double slit experiment, considering that he apparently performed it circa 1801, and the experiment apparently needs a coherent light source?
According to what I've been able to dig up in books, Young didn't actually use a double slit, but rather a thin piece of card dividing the thin beam of (I'm guessing- non-coherent light).

Have you actually seen the famed Double Slit experiment utilizing sunlight, or any other form of projected non-coherent light (IRL)? Or is this explanation of the experiment just incorrect?
Or is it correct, but I'm misunderstanding something?

Thanks in advance

There'll still be some degree of coherence in thermal light. Just not nearly as much as in a coherent source like a laser. Think that's why you get blurred, smeared out fringes as opposed to sharp ones for the old-style double slit experiment.

 

[kangitanka]

I recently read that a Microwave oven works utilizing kinetic energy within the water molecules (usually) in food.
Essentially, the water is a dipole and the molecules keep "flipping" themselves back and forth to match the alternating field of the microwave radiation.
Essentially, it's "internal" kinetic heating as the water molecules (and to a lesser degree, fats) essentially rotate back and forth within the food, creating kinetic energy and therefore friction, thereby heating up the food.

Is this correct, or am I completely off base?

Thanks

 

[kangitanka]

More generally, a flow of charged particles, under the influence of an electric field. Conductive medium isn't exclusive either. Charge in insulators will move...just not necessarily flow.

Thanks
Now, do the charged particles actually *flow*, or do they (say electrons for one specific case) merely "bump into each other"?
I.E. as the "electricity" flows (let's say, down a wire), do the electrons actually flow or stream down a wire, or do the electrons merely "bump" into each other as the EM "wave" moves down a wire*?

*rather like water molecules pushing against each other to create a small wave after you drop a small stone into a puddle (just to make an analogy)

 

[kangitanka]

There'll still be some degree of coherence in thermal light. Just not nearly as much as in a coherent source like a laser. Think that's why you get blurred, smeared out fringes as opposed to sharp ones for the old-style double slit experiment.

Have you ever seen, IRL, the Young double slit experiment using thermal light?
Considering the year Young supposedly conducted this experiment, I would think that this would be a common thing to show up and coming physicists in college or university.
Objective and empirical is always better than what appears to be a thought experiment.

Have you seen this?

I'd love to know

ETA- if you have, and you know how to reproduce it utilizing thermally generated light, I would LOVE to know how to do it. Quite frankly, I would love to reproduce an 1803 experiment that seems to demonstrate the wave model of light.

 

[Cabal]

Thanks
Now, do the charged particles actually *flow*, or do they (say electrons for one specific case) merely "bump into each other"?
I.E. as the "electricity" flows (let's say, down a wire), do the electrons actually flow or stream down a wire, or do the electrons merely "bump" into each other as the EM "wave" moves down a wire*?

*rather like water molecules pushing against each other to create a small wave after you drop a small stone into a puddle (just to make an analogy)

I get you.

But no. In most conduction models one typically neglects the electron-electron interaction so I don't think electrons colliding is nearly as significant as the electrons colliding with the nuclei of the atoms in the conductor. When modelling these things one typically includes a term for the average time an electron can travel through the wire without undergoing a collision. Statistically, electrons can travel through a wire for longer or shorter than this time but it's less likely for them to do so.

There is no collective wave motion associated with all of the electrons as far as I know, think they're all individually doing their own thing, but one can still define certain average rates like collision time etc.

 

[Cabal]

Have you ever seen, IRL, the Young double slit experiment using thermal light?
Considering the year Young supposedly conducted this experiment, I would think that this would be a common thing to show up and coming physicists in college or university.
Objective and empirical is always better than what appears to be a thought experiment.

Have you seen this?

I'd love to know

ETA- if you have, and you know how to reproduce it utilizing thermally generated light, I would LOVE to know how to do it. Quite frankly, I would love to reproduce an 1803 experiment that seems to demonstrate the wave model of light.

Honestly not sure - may have seen it being done at high school but really can't remember for sure. I think one can maybe improve the degree of light coherence at the double slit by putting a single slit close to the light source (the closer the better as all light sources have a coherence length and time associated with them before it starts breaking down), but don't quote me on that.

What I HAVE done is single-photon interference at a double slit. That stuff is messed up.

 

[Cabal]

I recently read that a Microwave oven works utilizing kinetic energy within the water molecules (usually) in food.
Essentially, the water is a dipole and the molecules keep "flipping" themselves back and forth to match the alternating field of the microwave radiation.
Essentially, it's "internal" kinetic heating as the water molecules (and to a lesser degree, fats) essentially rotate back and forth within the food, creating kinetic energy and therefore friction, thereby heating up the food.

Is this correct, or am I completely off base?

Thanks

Pretty much. Water is polar, i.e. it has an electric dipole moment and the friction arises essentially from the water molecules spinning fast and smacking into nearby particles.

Ever heard of the Active Denial System?

 

[kangitanka]

I get you.

Thankee, I was hoping my analogy made sense (whether it was correct or not)

But no. In most conduction models one typically neglects the electron-electron interaction so I don't think electrons colliding is nearly as significant as the electrons colliding with the nuclei of the atoms in the conductor.

Okay (sorry, late here, I have to get up at 4 am), so am I understanding you by saying that conduction is "significantly" about electrons colliding with protons and neutrons?
If no, then I need perhaps a simpler "plain english" explanation.
If yes, then did that link I provided (bad physics) get it right or wrong?

When modelling these things one typically includes a term for the average time an electron can travel through the wire without undergoing a collision. Statistically, electrons can travel through a wire for longer or shorter than this time but it's less likely for them to do so.

So (please be patient with me) are you saying that "electricity" is at least partly electrons traveling through a wire until a collision is made?

There is no collective wave motion associated with all of the electrons as far as I know, think they're all individually doing their own thing, but one can still define certain average rates like collision time etc.

Sorry, when I said wave motion I wasn't clear.
One can measure, with the simple grade school experiment with iron filiings, the wave of EM through a wire. And the filings do move based on differing measurements of the "electricity" "flowing" through the wire.
When I was speaking of the "wave" that was all it was. Oddly, if one changes nothing (positioning, voltage, etc) the wave never changes, but the electrons (and atoms and nuclei collisions apparently) continue to happen.
I would think that one performing this experiment would see the EM wave in the filings constantly fluctuation, but it doesn't.



Sorry, went on too long with a *serious* lack of physics knowledge.

Your insights, again, always welcome (in as "plain english" as you can for me )

 

[kangitanka]

What I HAVE done is single-photon interference at a double slit. That stuff is messed up.

THAT was going to be my next question!!!!
You have DONE the "one photon at a time" double slit experiment?

Wow! ~jealous~
Yeah, that IS messed up, but very cool.

Now, correct me if I'm wrong, but aren't you the physicist who works on the "particles only, all the way down" assumption?
Or was that someone else?

 

[kangitanka]

Ever heard of the Active Denial System?

Yes, saw something on it on Discovery or NatGeo (can't remember which).
THAT sounds painful, especially at a potential range (not confirmed that I know of) of 1000 meters.

Dang, ouch, hurt, pain!


ETA
Bedtime for this dropout....4 am comes WAY too soon.

Looking forward to responses that I'll read tomorrow after I get home from work

 

[Cabal]

Okay (sorry, late here, I have to get up at 4 am), so am I understanding you by saying that conduction is "significantly" about electrons colliding with protons and neutrons?
If no, then I need perhaps a simpler "plain english" explanation.
If yes, then did that link I provided (bad physics) get it right or wrong?

So (please be patient with me) are you saying that "electricity" is at least partly electrons traveling through a wire until a collision is made?

What happens depends on what material you're talking about.

In the case of a typical conductor, say copper wire, electricity will without fail be carried almost exclusively by electrons. The collisions with the copper nuclei aren't part of the process, they're just what's going to affect the motion of the electrons in the wire. Collisions between electrons are less likely and thus less important when it comes to affecting their motion. (I only brought up the collision point in relation to your second question about wave motion.)

Different charge carriers and different collision rates will appear in different materials, e.g. in semiconductors like silicon you also have some positive charges contributing to the electric current. The link isn't wrong, just it's only electrons in the original example you cited.

Sorry, when I said wave motion I wasn't clear.
One can measure, with the simple grade school experiment with iron filiings, the wave of EM through a wire. And the filings do move based on differing measurements of the "electricity" "flowing" through the wire.
When I was speaking of the "wave" that was all it was. Oddly, if one changes nothing (positioning, voltage, etc) the wave never changes, but the electrons (and atoms and nuclei collisions apparently) continue to happen.
I would think that one performing this experiment would see the EM wave in the filings constantly fluctuation, but it doesn't.

Are we talking about AC or DC here?

 

[Cabal]

Now, correct me if I'm wrong, but aren't you the physicist who works on the "particles only, all the way down" assumption?
Or was that someone else?

Can't say that's me.....

 

[kangitanka]

Okay, one last burning question before I go to bed (yeah, I know "Get your butt to bed already!")
E=mc2
Going backward, what is the number for c2?
Is it 299,792,458 meters per second, squared?
Is it one light year squared?
When it comes to E=mc2, what is the actual number used for c?
I'm assuming that m= kilograms
Or is that incorrect?
And how is E measured?
What is the number for E that describes the amount of work that can be performed by the force provided by mc2?
What numbers (actual real world numbers) describe E and m and c2?

For example, I have a mass of circa 77 kilograms (which sounds MUCH better to my ears than my weight of 170 lbs )
What is my energy potential, and how much energy could my mass expend (considering complete mass to energy conversion)


Plain english explanations are best, of course
Or at least simple math

Again, thanks in advance
NOW I'm going to bed (and eagerly awaiting your responses to read when I get home after work)

 

[kangitanka]

Are we talking about AC or DC here?

That was DC when I experimented with it in early high school.


Ok, that's IT>
IM GOING TO BED NOW!
thanks for your responses, read the rest of yours after I get home from work tomorrow.

 

[Wiccan_Child]

i don't know much about physics. What is it?

The study of how things work, but on a more fundamental scale than biology (which is how living things work) and chemistry (which is how atoms and molecules, chemicals and substances, work). Currently, we have the Standard Model underpinned by Quantum Mechanics and General Relativity.

On a more serious note, what is electricity?
I know about the various ways to measure it (amps, volts, current, charge, etc, none of which *are* electricity), but what IS electricity?
I've heard from many (including teachers) that it is the flow of electrons through a conductive medium, but apparently that is not necessarily correct in all cases.
So, asking a physicist....what *is* electricity?

It's any net charge flux. Electrons aren't the only particles things which can carry charge, and you can get 'holes' of positive charge in an otherwise electrically neutral material which can flow (think of a hole in traffic that 'flows' backward as the cars move forward to fill its space).

But any charged particle or quasi-particle, when moving, constitutes electricity. More usefully, it's any substantial charge flow. That's why 'current' is so important and fundamental: it's literally the measure of how much charge is flowing.

Interestingly, the electrons in a material don't actually whiz round the entire circuit: they only move a small amount. They simply knock the electrons next to them, which allows the charge to keep flowing.
Also, electricity only flows around the outer edge of a wire, the so-called skin effect.

 

[Wiccan_Child]

Now, correct me if I'm wrong, but aren't you the physicist who works on the "particles only, all the way down" assumption?
Or was that someone else?

That was me, I think .

Okay, one last burning question before I go to bed (yeah, I know "Get your butt to bed already!")
E=mc2
Going backward, what is the number for c2?
Is it 299,792,458 meters per second, squared?
Is it one light year squared?
When it comes to E=mc2, what is the actual number used for c?

c is the speed of light as measured in metres per second, so it's exactly 299,792,458 m s[sup]-1[/sup].

I'm assuming that m= kilograms
Or is that incorrect?

It's in kilograms. Unlike other quantities in physics, the standard unit is the kilogram; other units generally have a standard unit, and a thousand such units are called a kilo-unit (e.g., joules to kilojoules, metres to kilometres). The kilogram is the standard unit of mass, not the gram, which is a strange case.

And how is E measured?
What is the number for E that describes the amount of work that can be performed by the force provided by mc2?
What numbers (actual real world numbers) describe E and m and c2?

E is the energy a particle has when it's stationary.
m is the mass of said particle when it's stationary.
c is the speed of light; it's a constant, regardless of what's going on.

For example, I have a mass of circa 77 kilograms (which sounds MUCH better to my ears than my weight of 170 lbs )
What is my energy potential, and how much energy could my mass expend (considering complete mass to energy conversion)

We simply plug it into the equation: E = mc[sup]-1[/sup] = 77kg * c = 23,084,019,266 J. Which is about 23 GJ, which is a lot of energy.

For comparison, the bomb dropped on Hiroshima released about 54-75 TJ. So if all the energy in 77kg was released in an explosion, it would be about 0.05% of the blast.

Interesting fact: when two protons collide at the LHC, they have about as much energy as when you clap your hand.

 

[Cabal]

That was DC when I experimented with it in early high school.


Ok, that's IT>
IM GOING TO BED NOW!
thanks for your responses, read the rest of yours after I get home from work tomorrow.

Ah, ok. That makes life easier. DC current involves the electrons propagating in one direction only. They won't have an oscillating EM wave associated with their motion as it's a completely different situation. The electrons will travel with the electric field, which in this case is pointing along the length of the wire (meaning the electrons will just conduct along it). The magnetic field associated with it is perpendicular to the electric field, which means you get a set of concentric circular field lines in the plane perpendicular to the wire.

They don't move because DC is effectively unchanging, mind you I doubt you'd see anything changing for AC either as iron filings are hard enough to move around with a magnetic field, it would have to be quite strong to move them that quickly and neatly.

Ferrofluid's cooler anyway.

 

[TerranceL]

Avvet did you come up with that "scientists party" thing on your own?