@M.N.Raia no, she is a well established physicist. She had to leave academia because she didn't manage to get off the postdoc treadmill, and I wouldn't blame her for being a little bitter. She has a tendency to be critical of what she sees as hype in physics, and that has earned her a bit of a reputation as "anti-science", but I think this is unfair.
I guess you're thinking of her latest video Particle Physicists Continue Empty Promises. The title is a bit click-baity, but she is making what seems a good point to many people. She objects to the way many physicists are pushing to build a collider much larger than the LHC because she feels there isn't the theoretical justification for it.
Not everyone agrees with her (I don't) but she is presenting a point of view that does have its supporters in the physics community.
As we have developed the idea of Electric Field Lines from coulomb's law. If two equal and opposite charges are in plane all the effect of electric field vectors add to line joining the two points, means all the electric field lines of forces contribute to coulomb's force.
When more than two char...
I made animation. not just the Electric Field join the contribute to coulomb force. I found the Field above and below added as vector addition so resultant is again straight line.
@Azmuth If it reduces , Why again uses F = K qQ/ r^2 . Means more than two charges it should be useful. Because it only worked when all the E worked on one charge.
@JohnRennie Pls contribute. I am trying to explain again.
@123 The formula should be summation from (i=1) to n K (q_i Q)/r^2 for the force of all the charge on Q.
If there are n charges
@123 Would you mind if I suggest you some good book or material? You just have to read the chapter -1 of it, then try asking the question if your doubt persists? or you guess there are better ways?
@JohnRennie Most of her papers have 1 to 2 citations which she cited herself....
Case I : Two equal and opposite charges are in plane. Between two charges let say +q1 and -q2 , Let say q1 has 10 electric field lines. All 10 electric field line attract q2.
Case II : If more than two charges. q1 , q2, q3 are in plane. q1 has again 10 electric field lines . But 5 lines attract to q2 and 5 E attract q3. So, force must be reduced.
@123 Because you are thinking that number of field lines determine force, its wrong. It's the number of field lines per unit area, that determines the measure of force
@123 Depends where are you are at. For example, the number of field lines per unit area between 2 changes are much much higher than somewhere away at infinity
Two similar charges. Electric Field and Potential map
Two opposite charges.
Dear Pls see the pictures. My question is that coulomb force between two charges means all the force of q1 contribute to attract or repel q2.
but , when more than two charges whether it lie on the same line or in a plane. q1 force must reduce. because now part of q1 attract another charge and partial force attact or repel another charge. force should reduce.
In mechanics we have 10N force (as charge have). If i apply a force 10N on a box. Then i apply the same force on two boxes it should distribute between two boxes. but coulomb's law apply same force on each charge. It is not distributed. Why
@JohnRennie Pls explain this.
As you can see in pictures of 4 charges not all electric filed goes to the other charges. as in case of case charges. It should reduce and we can not apply coulomb's force
@JohnRennie @Azmuth dear did you get my point of question.
In mechanics we have 10N force (as charge have). If i apply a force 10N on a box. Then i apply the same force on two boxes it should distribute between two boxes. but coulomb's law apply same force on each charge. It is not distributed. Why
Let's pick up on this comment.
Give me a moment to draw a diagram:
Suppose the force is being exerted by a spring between the boxes. It exerts a 10N force on the right box.
If I understand you then you are saying we could add a second box like this:
@123 And now the 10N force is being exerted on both boxes i.e. the force on each of the two boxes on the right is only 5N. Is this what you mean?
@JohnRennie Thanks for the reply and sharing your knowledge. Yes you are right. May be this way i can explain better.
Electric Field Lines/Intensity (E) span complete space radially outward by charge q1. If i placed opposite q2 charge in space at some distance all E of q1 curved and attract q2 not just straight line. Because when i added upward and downward E vector there resultant is also straight line. I can come up with this result all E contribute to attract q2. not just E of straight line.
ecause the above and below forces also add up to straight line. so they are also contributing in attraction. What if i placed q3 charge. Now q1 electric field not all go to q2. because in their path there is another charge. Coulomb force should distribute between charges.
Now there are two springs, both exerting a force of 10N, so now the force on each of the two boxes is 10N making 20N in all. Then the force on the left box would be -20N to the left (by Newton's third law). Yes?
Now in this case all the force comes from one place. Means the span of force is straight line. But in the case of charges the force distribute in 3D space there span is whole space.
@JohnRennie for the contribution. My question is about span. In case of mechanics problem all the force (line of action) in the same line not distributed in the whole space 3D. But In case of charge it distributed in the 3D space.
The field is spread out through 3D space, but I think we need to be careful about the difference between the field and the force. The force acts only at a single point i.e. at the position of the charge.
@123 what isn't clear about the concept of the electric field?
@Ankit how could you tell the difference? You can measure your velocity relative to the universe as a whole, but how would you measure the velocity of the universe as a whole?
I can understand the mathematics of Field and can extract physical results from it. But sometime found problem in understanding to connect with physics and physical world. That's why i asked weird questions.
@123 The concept of a field is a bit weird once you start thinking about it. As you say it is mathematically well defined, but what actually is it? If you have some electric field and you point to some position in space what exactly is it that is present at that point due to the electric field?
And there isn't a good answer to this.
And the end of the day what physicists do is construct mathematical models that correctly predict what happens when we do an experiment.
When i draw the electric field as per function found all E of +q1 contribute to attract -q2 it moves change their direction. but if we placed q3 in the path of q1 E. It steal some part of the E which could not go to q2.
I means q1 has 10 Electric line in 3D. When only q2 in place all 10 E of q1 moves and attract q1. When q3 is also in place now how possible all 10 E of q1 goes to q2 and all 10 E goes to q3 at the same time. because q1 has only 10E not 20.
Right, but you seem to be saying that because a finite number of field lines have to be divided between two different charges then the force per charge must be reduced.
Yes i know Force can not be calculated by counting the field line. I have just used it as an example . So, i can explain my question. you already explained my question better.
How can q1 simultaneously exert a force on more than one other charges at the same time.
@JohnRennie May be my question part of it. Because when i placed q2 all force and direction of q1 changes.
@123 because q1 doesn't directly interact with the other charges. q1 creates an electrostatic field around itself, and then that field interacts with the other charges.
The field will interact with any number of different charges.
It means direction of field changes by placing other charges not force.
All the charges contribute to change in field which can be check by positive test charge. But the magnitude force by each charge on every others charges is same.
So to calculate the force on the charge q3 (for example) you add up the fields from all the other charges, E = q1, q2, q4, q5, etc, and then the force on q3 is just F3 = E q3
Means as i shared a picture. Where Electric Field is zero how can we use this E zero position. What information it give us, what is the application of Electric Field map.
Because as i placed new charge it creates its own field and interact with other. The whole system again reestablished and create new electric field.
What is the benefit to get the information of knowing E map. or potential map.
Is there any answer for that so, i need to explain my students. How it is possible for q1 can apply same force on every single charge.
The field is a function of the values and positions of all the charges. If we know the field at every point in space then we can work out where all the charges are and what their values are. But we can't do this just by measuring the field at one point. We have to know the field everywhere.
@JohnRennie I am young enough to use it more efficiently.
@JohnRennie Hmm... but they can ask same question if q1 has 10N force how q1 apply 10N on q2 and 10N on q3 and so forth. What is the explanation of this.
It's like when I drew the boxes and springs. In effect the field creates a spring between q1 and every other charge in the field. There isn't just one spring that needs to be shared. The field creates as many separate springs as there are other charges.
@knzhou Hey, this is not on the topic of arrival times but I looked at your github and your physics notes are beautiful. Is there any chance you have a template or .tex of some kind that I could look at?
if you know where to look, there's plenty of public record of me bashing it
it was fixed about a year ago, which made it substantially better
but it still has a tendency to pick up a variety of awful threads that do a poor job of representing the site to a wide audience, mostly due to self-reinforcing feedback loops that favour lowest-common-denominator content
I think my biggest issue with it right now is that we're not good at preventing off-topic questions landing on it. Our close review queue is too slow to stop a HNQ.
But that's less an issue with HNQ and more an issue with our general lack of close reviewers.
I had also pointed out (don't see it anymore) that you had literally answered like 6 questions that day, let alone the last week, and that was the only one you promoted.
If you can just stop answering for a few years, and also ask some really popular but easy classical mechanics questions when you know I'm online, that would be great.
oooooohhh, and @rob is just one cap short of the badge?
actually, y'know what
I'm announcing the PSE Epic Badge Sponsorship programme
if there's somebody with 49 rep-caps under their belt, I will happily donate 200 rep to nudge them over the edge
T&Cs: somebody else must nominate that user, and the nomination must point out an outstanding answer by that user, along with a short argument for why that answer is worthy of a bounty
you can hit +200 in a day and then later some user that upvoted you gets deleted, so the vote is gone but the counter towards the badge isn't taken away
@EmilioPisanty Yeah, I don't think deleted votes are accessible in SEDE (and probably not even internally, since SE always stresses how they can't easily restore deleted accounts or invalidated votes).
@JohnRennie I don't use hone for texting... Only reading..... not even whatsapp...I just ave 4 apps installed, JIO Care, Adobe acrobat, Adobe scan, Aarogya Setu (COVID19 Tracker)
@Azmuth According to who? Is India planning on just stopping all measures to prevent spread? If your numbers are fairly low right now I can't see how it would expect to bloom that much again unless people just stopped caring.
@Azmuth Yes, but you've only had like 7 million total cases so far, in 8 months of the virus. I'm not sure why it would expect to bloom even more in the next 4 months. US is less dense, and lower population, and they've still had more total cases than India. I really wouldn't expect India to explode like US did because US really screwed up their response; unless India just stopped trying to prevent spread...
@Azmuth India seems to be steadily decreasing cases in the last month though... I'm just wondering where you're coming up with such a huge number when all the data I see really doesn't suggest it's going to explode there.
Dear physicist pls suggest the best books for electricity and electromagnetism. For undergraduate which explains physics way. And seperate book for math way
@Azmuth What exactly is the "second wave"? What is going to cause that? IDK it just seems like you're assuming something far worse is going to happen when the data doesn't back it really.
@Azmuth India is still in decline right now. And you're literally calling for almost a 10 fold increase in cases in 4 months when the virus has been spreading for like 8. I just don't see where you're pulling these estimates from at all.
@Azmuth "The thing is India is about to get at least 50-60 million cases by next year Feb" This sounds a bit confident to state for something that could happen (and again I don't think the statistics really support such a huge bump in that period of time)
@Azmuth If you're making guesses don't state it as a fact. And then when someone questions where you're getting the info from, it's usually a good time to mention it was just a guess.
@Azmuth I don't find anything funny about throwing out random guesses as fact, especially when it takes you so long to say that you don't actually have any reputable source for it.
If you're just going to change your guess when someone calls it out, I don't see why we would think it any more than coincidence even if you wind up being right.