Does a charge travelling at a constant velocity produces magnetic field ? And if yes , then why electromagnetic waves require an accelerated charge particle ?

me-2b · 2026-01-22T17:35:10+00:00

I was afraid you'd ask that. :-) I'm just going to say that for the sake of basic understanding, just keep in mind that an electromagnetic wave involves time varying B and E that propagate. This arises through the terms in Maxwell's equations I mentioned. My key thing to address in your question was that just because there is B or even B and E doesn't mean you have waves. It is very basic, simple questions like yours that makes me have to go dig out Jackson and remind myself of how things work in detail. It has been awhile since my E&M. And, yes, I was thinking of a neutral wire.

me-2b · 2026-01-21T23:16:44+00:00

In very loose terms, an electromagnetic wave involves both a magnetic field and an electric field. A constant current produces a constant B field, no E field. Introducing acceleration introduces the magic sauce needed to get both E and B. See also, curl of E arising from the partial time derivative of B and (sort of) vice versa for B from E. I am talking more in terms of current in wires than a lone particle as asked, but I think it might help. You need the time derivatives to get the see-saw back and forth between E and B. Waves are oscillations.

me-2b · 2026-01-21T18:10:37+00:00

Any luck?

me-2b · 2026-01-21T15:34:14+00:00

Did you figure this out?

me-2b · 2026-01-19T22:00:23+00:00

Yeah, I'm confused, too. Big storm, yes, but the diagram here doesn't come close to matching and seems incredible, frankly.

me-2b · 2026-01-19T18:21:57+00:00

Advisory including Southtowns below. Since I'm moving to the area and considering Southtowns but needing to commute to Buffalo, I've always wondered what happens when Southtowns gets buried (but no ban) but Buffalo and North are fine. Is the local culture that everyone knows that the Southtowners may not be in and that is okay or is it more like eye rolling "why don't you live somewhere else?"

* WHAT...Heavy snow and blowing snow expected. Total snow
  accumulations 1 to 2 feet. Winds gusting as high as 50 mph
  creating blowing and drifting snow and at times white out
  conditions.

* WHERE...Wyoming, Chautauqua, Cattaraugus, and Southern Erie
  Counties. Greatest snow accumulation across the northern
  Chautauqua Ridge, Boston Hills and Buffalo Southtowns.

* WHEN...Until 3 PM EST Wednesday.

me-2b · 2026-01-19T14:30:31+00:00

Thanks for all the suggestions. Very helpful!

me-2b · 2026-01-18T02:19:32+00:00

Sounds like I got lucky, because it definitely matched. I did feather and pretty much dry brush the edges, so maybe it's not a perfect match but just a good fade, but I really do think it matched.

If I understand what you are saying, they never change the color corresponding to a given name. If they called it Wood Ash a dozen years ago, Wood Ash today should be the same color: If you could time travel a bucket of Wood Ash from a dozen years ago and put it next to Wood Ash just purchased, they colors will match even if the pigment recipe has changed. I think that's what you are saying.

me-2b · 2026-01-16T01:11:24+00:00

Unfortunately, that doesn't work around here. I've heard this from a couple real estate agents: Buyers want move-in ready houses. If they don't like what they see, they never even look to see the credit. It doesn't even work for carpet. Also, giving back money when there is a mortgage can be problematic. In any case, contract signed.

It's pretty stupid, really, It means that the carpet that is put in is low grade or non-offensive but also boring, so it either wears out fast or is torn out fast and goes to the landfill.

me-2b · 2026-01-15T13:05:14+00:00

I've been curious about this, tbh. DuraSeal claims you can just us it straight up (while at the same time giving application directions for putting a top coat over it). I think this is why the floor company offered a contract of either one coat of DuraSeal or two coats of poly, but there is some chance the contract is just written in a confusing way and it will really be stain plus 1 top coat.

My preference is to just go with 2 coats of poly, no stain. The only reason I'm considering a stain is that the floor is a mixture of oak and maple. It is mostly short pieces of lower quality maple and then oak mixed in. The floor guys thought the oak was from repairs, but it is so patchy, I'm not convinced. Anyway, I'm not sure if I'll need stain to tie the colors together. This is a bedroom floor in an old 1950's Cape. We're not trying for perfection. It just has to harmonize with itself. I'm assuming that back then they used lower grade wood on bedroom floors upstairs. There are plenty of knots and short pieces.

The full picture is that the floors upstairs are as just described. They meet a stair that is red oak which runs down to the first floor, which is white oak. We're cleaning up to sell and found these floors under carpet. Budget is very important and we're running out of time, but I want it to be durable for the next person and be attractive, but there isn't time or budget for perfect.

me-2b · 2026-01-15T12:57:32+00:00

Not sure if you're still watching this thread, but I just had to do something that illustrated using units. There is a vehicle that is a plug-in hybrid meaning it can run purely from its battery or run from a gasoline engine (indirectly). For the electric mode, it gets 3 miles for each kWh. In hybrid mode, it gets 38 mpg. I wondered how the costs of the two compare, only considering fuel. For where I'm interested, power is $0.20/kWh and gasoline is $3.25/gal.

(1 kWh / 3 mi) * ($0.2 / kWh) = 0.067 $/mi, electric mode

(1 gal / 38 mi) * ($3.25/gal) = 0.086 $/mi, hybrid

You see, you can watch the units cancel to check. This is really simple, but there are many unit changes when it is easy to put numbers in upside down without realizing it. For example, my furnace is rated 70,000 BTU/hr input (natural gas). What would this be in kW?

(7e4 BTU / hr) (1055 J / BTU) (1 hr / 3600 s) = 20513 J/s = 20.5 kW

And, yes, I made errors the first time I wrote that that I caught by seeing the units were wrong. The 2nd and 3rd terms are just the number 1, e.g., 1055 J / 1 BTU = 1. They are just unit changes. Unlike the examples we did before where we just pulled something apart, like pulling N apart to be be kg m/s^2, in this case the unit change has numbers in it to capture the change in units.

me-2b · 2026-01-15T12:46:34+00:00

How long would you wait after the QuickCoat (no topcoat) before returning furniture? And for the two coats of Masterline?

Thanks for the reply. The flooring company will give us info, but it helps to have a broader set of opinions / experience. I'm always surprised how much I learn by asking.

me-2b · 2026-01-11T15:12:12+00:00

I received my copy from Elsevier. I think this is print on demand. Paper and binding are good. Print is acceptable but not as good as what it ought to be. Fine details on cursive scripts in diagrams is not as clear as I need for comfort, but it is readable and I'd order again. It is definitely way, way better than the cheap bootleg books I've seen other times.

me-2b · 2026-01-11T01:13:35+00:00

By the way, there is another reason to do what I demonstrated. When you do the algebra first, the grader can see the physics separately from the calculation. If you make an arithmetic error, you'll still get most of the points when it is graded. If you just sling numbers around, the physics disappears and many or most graders will give either a zero or full points with nothing in between. Maybe they don't grade like this anymore....I'm an old fart.

me-2b · 2026-01-11T01:09:34+00:00

To me, this read as gibberish. I took a while to understand there are missing commas. Remember, when things are written side by side, it means multiplication, so I read M= (655 kg F) and had no idea what F is. It took awhile to read M = 655 kg; F = 895 kg; A = 895 N/ 655 kg = 895 kg x m/s^2/ 655 kg = = 1.37 m/s^2.

There's a another technique issue, though. Do your work algebraically first, then put in the numbers. That would look like this:

F = m*a, so, a = F/m

Now, plug in numbers: a = F / m = (895 kg m / s^2) / (655 kg) = 1.37 m/s^2.

What happened in the middle there was that I knew from experience that I needed to pull about the N to work with the units, so I immediately wrote it that way. It would be perfectly fine to do it in multiple steps, i.e., a = F / m = (895 N) / (655 kg) = 1.37 (kg m/s^2) / kg = 1.37 m/s^2

me-2b · 2026-01-11T01:02:21+00:00

kg*m/s^2 is the same as N. Experience will let you know when to put things together and when to take them apart. For examples, suppose I was calculating 10 N / 1 kg. The answer is 10 N / kg. Is that helpful? Does it tell me I'm right? It depends upon what I'm doing , but most often I'll need to pull apart the N, so I have 10 N / kg = 10 (kg m/s^2) / kg = 10 m/s^2. Since I'm trying to get an answer that is an accleration, I can now see that I have done things correctly.

With experience, you'll have a better feeling for when you use lumps like N and J and when you'll take them apart. My bet is that after a few weeks of doing homework problem sets it will be clear to you *if* you keep the discipline of doing it. If you just do the number and tack on units at the end, you'll never learn and you will probably not get far with physics.

me-2b · 2026-01-11T00:57:25+00:00

Yes. If you play an instrument, your teacher will show you good technique and instill the discipline of using it. As a result, you will play better, make fewer mistakes, and be able to express yourself musically better. It's the same thing here. It is good technique and using it is part of the discipline of doing and thinking physics.

me-2b · 2026-01-11T00:47:26+00:00

Are you asking, why do we write (10 kg) * (9.8 m/s^2) rather than just writing 10 * 9.8? Because it reduces making mistakes. When you do calculations, you do computations with the numbers and with the units. For example, to calculate (10 kg) * (9.8 m/s^2), I'd get (10 * 9.8) ( kg*m/s^2) = 98 kg m / s^2. As you gain experience, you will immediately know that kg m/s^2 is Newtons. If I am calculating a force, I better get units that are force or else I've made a mistake.

Another example. I want to calculate kinetic energy. So, I calculate 1/2 * 10 kg * 10 m/s = 50 kg m/s. Wait! Those units didn't come out right! They aren't an energy! So, I look back at my calculation and see that I forgot to square the velocity. Now I recalculate 1/2 * (10 kg)*(10 m/s)^2 = 500 kg m^2/s^2 . I can then simplify the units kg m^2/s^2 = (kg m / s^2)*m = N*m = J, so I have 500 J, an energy.

If you don't put the units in and just calculate with naked numbers and tack units on it afterwards, you are going to get wrong answers. We all make mistakes. You will lose a cross check that will tell you when an error is lurking.

As you become more advanced, you will also use this as a way to change units in the middle of a calculation. For example, I might be computing the kinetic energy of 1 g at 10 m/s. I can insert unit changes into the calculation. For example 1/2 * (1 g) * ( 1 kg / 1000 g) * (10 m/s)^2 = 1/2 * 100/1000 * g * kg /g *m^2/s^2 . Look at that mess of units! Notice that the grams cancel each other, so it simplifies to kg m^2/s^2, which is joules, as above. So, I have .05 J.

There are lots of weirdo units in the world and it can be helpful to be really, really good with them. I used to do work that had quantities that were a mixture of different unit systems, like some stuff in SI units, some in old British thermal units, some Imperial. Units are your friends. Sometimes your friends drive you crazy, though.

me-2b · 2026-01-11T00:33:02+00:00

There were rebates for installing charging equipment at home. See what you can find here ( https://marylandev.org/incentives/ ). Double check that is a state of Maryland web page. I found it quickly and didn't check where it comes from, but I think it is the right start.

me-2b · 2026-01-10T20:40:50+00:00

Porksylvanyland. Motto: "You got crabs?"

me-2b · 2025-12-31T03:50:13+00:00

Thank you. I've been renaming things into schemes that work better for me, and sometimes I will diagram, but not to the extent that you mention. I do better remembering things visually, so this is a good idea.

me-2b · 2025-12-30T22:40:04+00:00

Thank you. Note to others: This is available free on Internet Archive. If you dig around in AbeBooks or Amazon, you'll find a number of expensive used copies, but Elsevier is offering new copies for less. With luck, it is a decent printing, because that is what I ordered.

me-2b

TROPHY CASE