In the Coulomb force equation (F=Q1Q2/4 pi E r^2) one of the Qs will be the test charge q, so that is the one that is divided. The other one is the substantial charge.
Each playlist contains videos in the order in which I think they can be best and most logically viewed if you want to view the complete set. Alternatively you can select a particular video, although in some cases I may make mention of information derived in another video. In most cases these will be earlier videos in the playlist but occasionally I cross refer to other videos elsewhere on the channel, to avoid too much duplication of material.
This is the essence of scientific method. Scientists observe the real world and then attempt to account for it both in terms of explaining what is happening and, where possible, assigning a mathematical representation. The key to all theory is that it must fully and accurately describe what we already know and forecast something else that can be tested by experiment. If the experiment agrees with the theory, then the theory can be developed. If not it must be changed.
I'll explain in more detail in next vid on Maxwell's equations. But in essence E = Q/4π r2 ε. V is defined as electric potential energy per unit charge = Force x distance / charge. Force = Qq/4π r2 ε. So V = Q/4π r ε. Do E = V/r (or V/d if you use d instead of r). So E can be measured either in units of newtons per coulomb or volts per metre.
At 6:50 the E at the top of the screen is the Electric Field strength = F/q. The E at the bottom of the screen is Electric Potential energy. Energy = force x distance = Fr. So Electric PE is Qq/4 pi ε r2 x r = Qq/4 pi ε r
r is indeed the complete distance. It does not stand for radius. It is simply a distance parameter. So when F=q1 q2/ 4 pi epsilon r^2 then r is the total distance between q1 and q2.
Not sure what you mean by EM force field. There are electric fields & magnetic fields. A charged particle in an E field and a moving charged particle in a B field (or a moving B field) will experience a force. So the field is really the potential to exert a Force if there is something in that field on which a force can be applied. eg the electric field has no impact on a neutron. There is electromagnetic radiation which consists of a travelling electric field with associated mag field.
Are the Q's interchangeable? I am referring to the point at around 5:30 where you quickly explain that you can cancel out one of the capital Q's with a small q. I always have problems with the mathematics rather than the concepts and am not sure if I just misunderstood what you were trying to explain. Thanks
I'll have a go, but meanwhile are you aware of the excellent video lectures by Prof Walter Lewin on Electricity and Magnetism made by MIT which, among other things, derive Maxwell's equations.
When you have 2 particles of the same charge and move one from infinity to a distance r from the other, then the potential at point r equals the work done in bringing the charge from infinity to r. In the case of opposite charges, at infinity the PE=0. As you bring the charge from infinity to r it has the capacity to do work. Work is integral of force x dist eval from infinity to r. F=kQq/r^2. Integral=-kQq/r. PE is negative. PE decreases as r decreases. Similar to gravitational PE.
No because the formula is calculating the difference in potential energy between being an infinite distance away from Q (PE=0) and a distance r away from Q.
Thank you very much for the video. I learnt much more about electric filed than my physics taught in whole month. And please upload video about capacitor too. like capacitance,spherical capacitor,parallel plate capacitor,its principle,combination of capacitors, energy stored in charged capacitor,energy density,loss of energy in joining capacitors,charging and discharging of capacitors. And also about the dielectrics. Thank you very much.
It covers material in the AQA, OCR and Edexcel syllabus and I have also added some material from the CIE syllabus. I cant guarantee that it covers everything. If anyone spots gaps, let me know and I'll try to add more videos to cover them.
+Rainbow Rose The electric potential is defined as the work done by an electric field in carrying a unit positive charge from infinity to that point. Potential difference is just the difference between the electric potentials at different points.
I understand that the term 1/r describing the potential energy can be derived by integrating the force from "infinity" to the distance r. However, I somehow completely fail to see why that should be equal to the potential energy at that point in the case of attraction, since in that case the distance from infinity to r has nothing to do with the distance where the force is aplied. Also the integration gives the term -1/r, allowing "Ekin+Epot=0", which is not explained here.
Hi drA , this is a question that a really need an answer ; how do scientists come up with these equation , why do they for example devide the Q1Q2 over the free space permitevity times 4pi ... or in the equation of gravity that newton came with where he devided by r^2 and multipled by G the gravitational constant ? Hope I get an answer thanks
Hello, Thanks for your response. Yes, the annotation appears correctly on my PC. Indeed, I watched your video on my tablet with the youtube apps (and also the mobile version of youtube with Chrome) and unfortunatly the annotation does not appear (I've just checked). Nevertheless, by forcing to use the computeur mode with Chrome with my tablet, we can see the annotation. Thank you.
The 4piEo with respect to charge is a constant in which case CQq similar to gravity of GMm for the formulas at the end. One questions if dark energy is a kind of inverse gravity, in which case it may be possible to shield oneself from it. Further if positive fields go out and negative in - is this just as we have chosen to look at it I.e. inverting the negative could be viewed as out and positive in??
Since electric flux is the amount of the electric field passing through a particular area (window), the net electric flux will be zero if the amount of the electric field passing out the window is the same as that passing in.
Its all wonderful ,Thank you very much, but what about Practical physics? particle detection, How to investigate the decay curves for capacitor circuits are exponential . and such things
For electric potential energy, since it is defined as 0 from a main charge Q. If the force between the charges is attractive then does that mean that as little q is moved closer it loses electric potential energy?
At the very end when you said that the difference in PE GMm(1/r1^2 -- 1/r2^2) for a gravitational field. Why is it "r^2" instead of it just being just "r"? And also why is it that for the PE of the electric field.
Sir, the cambridge coursebook says that, potential V at a distance r from a charge Q = Q/(4*pi*epsilon not*r^2) Can you please explain why it is not r, according to your equation of V
If I have 3 densities of charges, and when I add them up if I get a negative result, when I calculate the electric field between plates using E= sigma/2episilon 0, will the electric field be negative?
I don't understand why with opposite charges the potential energy has to be derived from the work done in bringing something in from infinity. When the charges are let go, the potential energy will convert to kinetic energy, while the charges accelerate towards each other. Why (I know the formula is wrong) is the kinetic energy not equal to the integral of the force from 0 to r, since that should be the work done in bringing the charge there from a state where PE=0?
This video is great and very informative. The only bit that confused me was when you used the notation of 'E' for potential energy, when E is already used the state electric field strength. After it was corrected it was fine but before I couldn't see where any of the equations were coming from. Maybe try using 'W' instead :)
Feedback: last seconds before the video end: Change in Electric Potential Energy = Charge x (potential change) ..... (1/r2 - 1/r1) instead of (1/r1 {squared - 1/r2 {squared}}) as potential proportional to 1/r and with negative sign.
Could you please arrange the video's in the playlists in order in which they are meant to be viewed? I tried follow the present order but then you keep telling to view the "other video" :( Sorry for the rant but would be much helpful to many people if the videos were in order.
So when you say voltage in this video, you know without the potential difference, what are you referring to? That point potential compared with 0(infinity)?
Hi isn't the potential energy supposed to be inversely proportional to r rather than r^2? However at the end of the video while comparing the similarities between the change in pe for g field and e field it seems to reflect otherwise. Correct me if i'm right and thanks for your videos!
Am i right in saying that actually the minus charges move toward to positive? Because i am getting really confused now, i was okay with simple electricity being reversed but now it makes no sense... :(
ahh ok thank you, i was equating e/b field strength with the kind of force you would experience due to gravity, but i didn't take into account the necessary charges. Let's say that I put a shirt on with 10^10000000000 negative charges and stood in front of a large positively charged metal plate, In my mind I thought the force of the interaction could A. Pull the metal plate towards me, or B.See a rather large electric charge jump off of the plate into my chest haha
Is 4pi used because the field is moving either outward from a point or inward towards a point in all directions (spherically?) I get confused as to why sometimes pi is used in equations, but other times it's 2pi, 4pi, etc. Is there some underlying principle to tell you what to multiple pi by under a given context? Thanks for these videos. They are very good!!
At an infinite distance from a field causing charge Q I have some ambiguity with regards to the Kinetic Energy of an unit positive charge - my understanding is that Etotal=Ek and it is hence maximum as the potential energy is converted to kinetic energy. However, I also understand that E is inversely proportional to r^2 so wouldn't that suggest that the charge decelerates and becomes stationary at infinity? Thank you in advance!
It depends on the signing convention. We usually say that when an object is at an infinite distance away then its potential energy is zero and its kinetic energy is zero. Since energy can be neither created nor destroyed the total energy at all points along the trajectory to infinity must also equal zero. Since it will have positive kinetic energy we therefore say that it has negative potential energy. But as I say, that is all just a matter of the signing convention.
Damn he knew we all would need this one day.legend.
(8 years ago. Just wow )
😂😂😂😂
its been a whole decade now
mans still helping a lvl students all over
do you have small writing or a long sheet of paper?
both i guess
finally. the real question is being asked
Thanks for kind comments. There are videos on Capacitors and Dielectrics in the Electricity & Magnetism playlist. Hope they help.
In the last part of the video (The Potential energy), it's not over the distance squared, it's only over the distance !!
I was wondering about the same thing.
Same thing. Obviously we are human so it is mistaken, it is divided by sqr(separation).
@@fredy749 not at all the same thing
@@YesIlikebananasSo bruh.. they're referencing to them thinking the "same thing".
Right as par the derivation ✅
The myth, the legend, the prodigal son : DrPhysicsA
In the Coulomb force equation (F=Q1Q2/4 pi E r^2) one of the Qs will be the test charge q, so that is the one that is divided. The other one is the substantial charge.
Well spotted. Thanks. I have added an annotation to make the correction.
Each playlist contains videos in the order in which I think they can be best and most logically viewed if you want to view the complete set. Alternatively you can select a particular video, although in some cases I may make mention of information derived in another video. In most cases these will be earlier videos in the playlist but occasionally I cross refer to other videos elsewhere on the channel, to avoid too much duplication of material.
Thanks. I had spotted this. I had put an annotation on the video to make the correction.
This is the essence of scientific method. Scientists observe the real world and then attempt to account for it both in terms of explaining what is happening and, where possible, assigning a mathematical representation. The key to all theory is that it must fully and accurately describe what we already know and forecast something else that can be tested by experiment. If the experiment agrees with the theory, then the theory can be developed. If not it must be changed.
I'll explain in more detail in next vid on Maxwell's equations. But in essence E = Q/4π r2 ε. V is defined as electric potential energy per unit charge = Force x distance / charge. Force = Qq/4π r2 ε. So V = Q/4π r ε. Do E = V/r (or V/d if you use d instead of r). So E can be measured either in units of newtons per coulomb or volts per metre.
i am from morocco, we study in frensh, but i understand much better with your videos even they are in english,, thank u sir,, you'r doing very well
At 6:50 the E at the top of the screen is the Electric Field strength = F/q. The E at the bottom of the screen is Electric Potential energy. Energy = force x distance = Fr. So Electric PE is Qq/4 pi ε r2 x r = Qq/4 pi ε r
Try "Classical Mechanics - A Level Physics" in the A level Playlist on my main page.
r is indeed the complete distance. It does not stand for radius. It is simply a distance parameter. So when F=q1 q2/ 4 pi epsilon r^2 then r is the total distance between q1 and q2.
Not sure what you mean by EM force field. There are electric fields & magnetic fields. A charged particle in an E field and a moving charged particle in a B field (or a moving B field) will experience a force. So the field is really the potential to exert a Force if there is something in that field on which a force can be applied. eg the electric field has no impact on a neutron. There is electromagnetic radiation which consists of a travelling electric field with associated mag field.
Are the Q's interchangeable? I am referring to the point at around 5:30 where you quickly explain that you can cancel out one of the capital Q's with a small q. I always have problems with the mathematics rather than the concepts and am not sure if I just misunderstood what you were trying to explain. Thanks
I'll have a go, but meanwhile are you aware of the excellent video lectures by Prof Walter Lewin on Electricity and Magnetism made by MIT which, among other things, derive Maxwell's equations.
great, I will try them
When you have 2 particles of the same charge and move one from infinity to a distance r from the other, then the potential at point r equals the work done in bringing the charge from infinity to r. In the case of opposite charges, at infinity the PE=0. As you bring the charge from infinity to r it has the capacity to do work. Work is integral of force x dist eval from infinity to r. F=kQq/r^2. Integral=-kQq/r. PE is negative. PE decreases as r decreases. Similar to gravitational PE.
The man the myth the legend Dr physicsa. Can you make a vid on Thermometers and energy changes
No because the formula is calculating the difference in potential energy between being an infinite distance away from Q (PE=0) and a distance r away from Q.
Thanks so much, it's much easier when I can rewind it and when it is laid out properly.
Thank you very much for the video. I learnt much more about electric filed than my physics taught in whole month. And please upload video about capacitor too. like capacitance,spherical capacitor,parallel plate capacitor,its principle,combination of capacitors, energy stored in charged capacitor,energy density,loss of energy in joining capacitors,charging and discharging of capacitors. And also about the dielectrics. Thank you very much.
best explanation of electric fields thank you
Potential is ~1/r, NOT 1/r^2
This guy's enthusiasm is amazing. Thumbs up from me !! 😄
It covers material in the AQA, OCR and Edexcel syllabus and I have also added some material from the CIE syllabus. I cant guarantee that it covers everything. If anyone spots gaps, let me know and I'll try to add more videos to cover them.
Link the other videos in the description please, Thanks for making these videos, I was having huge trouble understanding fields.
I admire Dr physicsA youtube channel ! I have a suggestion : Why don't yo do lectures on Algorithms and theoretical computer science ?
Sir, can you please explain the difference and relation between electric potential and potential difference
+Rainbow Rose The electric potential is defined as the work done by an electric field in carrying a unit positive charge from infinity to that point. Potential difference is just the difference between the electric potentials at different points.
Well it's pretty easy to tell as the word difference suggests
You are the best teacher... Thanks
what can the actual force of an electric field do when compared to an electromagnetic force field?
I understand that the term 1/r describing the potential energy can be derived by integrating the force from "infinity" to the distance r. However, I somehow completely fail to see why that should be equal to the potential energy at that point in the case of attraction, since in that case the distance from infinity to r has nothing to do with the distance where the force is aplied. Also the integration gives the term -1/r, allowing "Ekin+Epot=0", which is not explained here.
Hi drA , this is a question that a really need an answer ; how do scientists come up with these equation , why do they for example devide the Q1Q2 over the free space permitevity times 4pi ... or in the equation of gravity that newton came with where he devided by r^2 and multipled by G the gravitational constant ? Hope I get an answer thanks
Hello,
At the end of your video, the potential energy must vary as 1/r instead of 1/r^2.
Thanks
Yes. I did put an annotation on the video to clarify this but I understand that not everyone can see the annotation.
Hello,
Thanks for your response. Yes, the annotation appears correctly on my PC.
Indeed, I watched your video on my tablet with the youtube apps (and also the mobile version of youtube with Chrome) and unfortunatly the annotation does not appear (I've just checked).
Nevertheless, by forcing to use the computeur mode with Chrome with my tablet, we can see the annotation.
Thank you.
@@olivierlaurent1409, how did your exam go? This is 4 years later so i understand if you don't reply. Hope you're doing well
@@zeyn4792 How did YOUR exam go ? 2 years later lmfao hope ur doing well tho
The 4piEo with respect to charge is a constant in which case CQq similar to gravity of GMm for the formulas at the end. One questions if dark energy is a kind of inverse gravity, in which case it may be possible to shield oneself from it. Further if positive fields go out and negative in - is this just as we have chosen to look at it I.e. inverting the negative could be viewed as out and positive in??
have you got videos on momentum laws? conservation of momentum and kinetic energies?
Are electric fields diverted towards conductors like copper wire in a circuit?
Electric field stength is the force per unit positive charge.
Since electric flux is the amount of the electric field passing through a particular area (window), the net electric flux will be zero if the amount of the electric field passing out the window is the same as that passing in.
then shouldnt the r be from q to the middle dot as that is the distance travelled ?
Can you explain potential energy when the test charge is -ve instead of +ve?
Hello,
could you explaine the diffrent advantages of (or between) electics fields and maghnetic fildes in practice.
Its all wonderful ,Thank you very much, but what about Practical physics? particle detection, How to investigate the decay curves for capacitor circuits are exponential . and such things
Doctor how do we derive did the rule of electric potential energy ( Q/4Pi€ r )
made everything so clear
For electric potential energy, since it is defined as 0 from a main charge Q. If the force between the charges is attractive then does that mean that as little q is moved closer it loses electric potential energy?
You, my friend, are a fucking lifesaver.
At the very end when you said that the difference in PE GMm(1/r1^2 -- 1/r2^2) for a gravitational field. Why is it "r^2" instead of it just being just "r"? And also why is it that for the PE of the electric field.
TheGoldenEagles100 dude its coz W=Fx..so F=Qq/4pi*r2 x r which cancels the r..so its left r
Can someone explain please
Sir, the cambridge coursebook says that, potential V at a distance r from a charge Q = Q/(4*pi*epsilon not*r^2)
Can you please explain why it is not r, according to your equation of V
+Rainbow Rose At what time on the video does this arise?
+Rainbow Rose i didnt get it
+Rainbow Rose he wrote Q/(4*pi*epsilon*r)
sir , I feel confusing about when it will be 'r' and when will it be 'r^2"
+Rainbow Rose There is a printing mistake in the book
DrPhysicsA is correct
thanks Drphysics you are really awesome !
Man, you're godsend!
If I have 3 densities of charges, and when I add them up if I get a negative result, when I calculate the electric field between plates using E= sigma/2episilon 0, will the electric field be negative?
I don't understand why with opposite charges the potential energy has to be derived from the work done in bringing something in from infinity.
When the charges are let go, the potential energy will convert to kinetic energy, while the charges accelerate towards each other. Why (I know the formula is wrong) is the kinetic energy not equal to the integral of the force from 0 to r, since that should be the work done in bringing the charge there from a state where PE=0?
I like the classic and simple way of explanation. With due respect there are minor technical mistakes in the video.
at 5:28 you gave the definition of electric potential as electric potential energy
You might find my video on electromagnetism helpful.
This video is great and very informative. The only bit that confused me was when you used the notation of 'E' for potential energy, when E is already used the state electric field strength. After it was corrected it was fine but before I couldn't see where any of the equations were coming from. Maybe try using 'W' instead :)
Feedback: last seconds before the video end:
Change in Electric Potential Energy = Charge x (potential change) .....
(1/r2 - 1/r1) instead of (1/r1 {squared - 1/r2 {squared}}) as potential proportional to 1/r and with negative sign.
Okay i get it.. thank you :)
your videos help me out soo much
Could you please arrange the video's in the playlists in order in which they are meant to be viewed? I tried follow the present order but then you keep telling to view the "other video" :(
Sorry for the rant but would be much helpful to many people if the videos were in order.
at 6:5 9 why do we take r and not r^2?
at 6:50 why r and not r^2 ???
You are the best sir! :)
Thank you
The gravitational potential enger is GMM(1/r2 - 1/r1) its not squared
Is this for OCR A Physics please respond asap!!!
How do you get E = V/d ?!
Thanks for comment. The link to the full playlist of my A Level Physics Revision Videos is now in the description.
Sir can you see my videos on RUclips
hello
can you make a video on as level electric current and DC circuits
That material should be in the A-level physics revision playlist.
thank god i found you , you are my life saver ;p
Shouldnt V be the electric potential difference between two positions in an electric field?
Yes. Any potential is always given in terms of a potential difference with respect to some other point
So when you say voltage in this video, you know without the potential difference, what are you referring to? That point potential compared with 0(infinity)?
from wich book you get all this?
Hi isn't the potential energy supposed to be inversely proportional to r rather than r^2? However at the end of the video while comparing the similarities between the change in pe for g field and e field it seems to reflect otherwise. Correct me if i'm right and thanks for your videos!
Correct me if i'm wrong*
+abcxyz518 At what time on the video does this arise?
+DrPhysicsA 16:00
@@aeroscience9834 Mans left you hanging for 5 years lmao
best video tysmmmmmm
thanks bro. R u by any chance related to the show Dr. Who ? lol
Am i right in saying that actually the minus charges move toward to positive?
Because i am getting really confused now, i was okay with simple electricity being reversed but now it makes no sense... :(
ahh ok thank you, i was equating e/b field strength with the kind of force you would experience due to gravity, but i didn't take into account the necessary charges. Let's say that I put a shirt on with 10^10000000000 negative charges and stood in front of a large positively charged metal plate, In my mind I thought the force of the interaction could A. Pull the metal plate towards me, or B.See a rather large electric charge jump off of the plate into my chest haha
You're Awesome! Thank You! Would greatly appreciate if you make videos on Maxwell's Equations as well! :-)
Is 4pi used because the field is moving either outward from a point or inward towards a point in all directions (spherically?) I get confused as to why sometimes pi is used in equations, but other times it's 2pi, 4pi, etc. Is there some underlying principle to tell you what to multiple pi by under a given context?
Thanks for these videos. They are very good!!
Thanks
THANKS
When is net electric flux zero?
Thank u💙💙💙💙
thank you
Is this relevant to AS
Nope
Thank you so much, appreciate your great effort!
Geshbeddin , the man is a very good instructor , if you don't like his vedios then don't watch it ,
Isnt K 8.99x10^9??
+Liam Hughes What value did I give? And at what time on the video?
thank you sir, i finally understood fields
Sir, is there any convention to using Q or q as charge?
you should have used Q and q to explained !
IM gonna fucking fail tomorrow
found this helpful ,thanks sir
thank you so much!
thank you you are excellent
Even after watch this video ??
where can ı found electric field questions?
You may find some in my video at AS Physics Exam Question: Electricity
thankk youuuu !!
Man can never be hot
is this AS or A2 ?
Both
+thesuperproify Mainly A2
At an infinite distance from a field causing charge Q I have some ambiguity with regards to the Kinetic Energy of an unit positive charge - my understanding is that Etotal=Ek and it is hence maximum as the potential energy is converted to kinetic energy. However, I also understand that E is inversely proportional to r^2 so wouldn't that suggest that the charge decelerates and becomes stationary at infinity? Thank you in advance!
It depends on the signing convention. We usually say that when an object is at an infinite distance away then its potential energy is zero and its kinetic energy is zero. Since energy can be neither created nor destroyed the total energy at all points along the trajectory to infinity must also equal zero. Since it will have positive kinetic energy we therefore say that it has negative potential energy. But as I say, that is all just a matter of the signing convention.