PHYS 102 | Magnetic Force on Charged Particles
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- čas přidán 31. 12. 2013
- A demonstration that the force a uniform magnetic field applies to charged particles makes them move in a circle.
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Damn. That's some real physics right there. I'm learning the theory and the math of eletromagnetism at school, but they don't tell us about the real thing. It's pretty cool to see it. I loved it, thank you
Yes the real thing is very different than theory. I have a lecture on electricity as explained by CP Steinmetz, based on field theory.
Also fascinating, and very different than quantum physics
You must not be theory-oriented if that's what you take from lectures. This demonstration is self-explanatory using Maxwell's equations and the Lorentz force, but you have to be well-versed with mathematical interpretation.
Probably an underrated channel
Very informative. It's useful for class XII physics.
Very nice demonstration, would have been also very cool to show what happens if you kept increasing the magnetic field. The beam would spiral towards a single point. Fun educational fact would also be that this is how nuclear fusion is being performed by squeezing charged particles to a single point using a strong magnetic field.
This made it click for me. Great demonstration!!
Thanks for the great visualisation
Man you are clear genius
Not really. The videographer who shot this is a genius. There was no light whatsoever! The beam is so dim!
Excellent teacher
@Physierge
1: if electrons are attracted to the plate, why wouldn't they curve toward and then onto the plate?
2: why wouldn't the electrons that got through get pulled back toward and then onto the plate?
3: why do the electrons stay in a uniform beam instead of immediately being repulsed by one another?
4: why do the electrons go though the plate and behave as though there is no repulsion or attraction?
They are attracted back but they gain so much kinetic energy while between the plates that you don't notice. It is like if you shot a ball at very high speed straight up. As soon as it is released it is falling back down, but it continues to go up for a long time.
Thank you, it is very good.
great video
Extremely cool. Thank you very much sir.
Very welcome
Thank you
You really deserve more likes and views
Thanks
Some questions regarding the experiment:
1) what would be the velocities of electrons coming out of the electron gun?
2) magnetic field during the perfect circle?
The same with which it started
Magnetic field cannot change the speed of the electrons it can only change the direction of velocity also radius is inversely proportional to Magnetic field so as it increase radius decrease formula r = mv/qb
the velocity of the electron would depend upon the potential difference which has been developed across for different delta V you could obtain different velocities
probably somewhere on the order of 6,000,000 m/s. Do the lorentz force calculation at this velocity to get the B field I don't have the energy for that rn
amazing!!
That's soo cool
Excellent demonstration. It would have been even better if the room was well lit before the commencement of demo so that the audience can see the setup of equipment. Its great to see the things in action rather than studying theortically from the text book. Overall its superb.
what is the limiting behaviour as you increase the strength of the magnetic field?
The radius of the circle would get smaller and smaller and eventually be limited by either the width of the beam, or by a "space charge" effect, which just means the charged particles being held so close together that they repel each other.
Lovely
Fantastic
It apears that direction of beam(decay?) Is locked.
Can you do the same with positron?
Love the video!
I have a stupid doubt,sir. Why don't the beam of electrons repel each other, because of their like charge? Shouldn't we see many lines of "excited gas" diverging out?
Please help me out.
Good question! Yes, that should and does happen, but the effect is small - meaning out much they spread is probably small compared to the diameter of the beam from the electron gun. I've never actually calculated it myself.
the force between even the the two electrons is of the order 10^(-29) as you could obtain this using coloumb s law and that is really very small to observe even i think that there would be symmetric repulsion from all the electrons in the beam hence which make this even more small
Thank you Physierge and Aditya’
Would you like to know how I could make this electron flow stay in getting aspiral?
The electrons (or any charged particle) will make complicated paths like spirals when the magnetic field is not uniform, like at the end of that bar magnet.
Very important knowlege!
Hey Professor,I think if you increase the current of the unionform of magnetic field,or accelerate the charged particle moving speed, the charged particle should do a helix movement.if you can prove this I will apperciate,thanks
+Yong Li, Just increasing the current will increase the strength of the field, and will just make a circle with a smaller radius (that is what I was doing with a knob). The radius of the circle is r = mv/qB. You are right though, if there is a way to change the particle speed, you could make a spiral. However, that is hard to do. An electric field could slow it down, but the direction is constantly changing... If we started applying E fields perpendicular to the screen, some interesting spirals could probably be made.
Hey Professor,it means a moving electron perpendicular to the magnetic field get two forces,one is Lorenz force and another force,the direction of this force is parallel to the magnetic field,it is the same or opposite to the magnetic field's direction depend on magnetic field strength
What if you make the magnetic field the opposite charge? Would you still get a circle?
When the electrons pass through the hole after accelerating towards it, why do they not decelerate after passing through?
This is a very good question - so good that it took be awhile to come up with a clear answer! :) The simple answer is, they do decelerate slightly. But, if you think in terms of forces from the charged plates, once they pass through the anode (and are pulled back as you suggest) they are still be repelled by the cathode as well!
If you think in terms of electric fields, consider the cathode and anode as parallel plates. In that case, the field outside the plates will be zero in the limit of infinite plates, but since they are not infinite there will be a small field pulling the electrons back.
Thanks. You answered my question. Between the plates you have a strong electric field. Beyond the plates the anode and cathode begin to have cancelling fields.
please please demonstrate the helical path of electrons also
If I turned the beam relative to the big current loops it might start to move in a helix, but the field is not strong enough to make the radius small enough that you could see it well. However, if you look at 0:58 when I bring the strong neodymium magnet nearby, you can see a non-uniform helical path.
Got that
Thanks🤗🤗
The light we're seeing here is pretty much the same thing as the northern lights, correct?
Pretty much. The gas they put in the bulb is probably different from whatever atmospheric gas makes most of the Northern Lights.
Sir where do u teach physics, can i contact u by any means?
I'm at Rice University. You can email me, that is fine.
Sir please tell ur mail.. I have alot of doubts regarding physics
Here electrons are accelerating so they should emit radiations and should lose energy resulting in decrease in velocity and radius, does this happens
Yes but at a rate so small you don't notice. Also keep in mind that this is not a continuous beam of the same electrons. it is constantly being resupplied by the source ("electron gun").
Damn👑
gooooddddddd
Hi prof, This setup looks very different in its make compared to ones available to buy. Can you please tell me how to (design) make it myself.
Hi, I'm pretty sure it was purchased by my department, probably decades ago. If you mean the big coils making the uniform magnetic field, the term to search is "Helmoltz Coil". The glass chamber with the beam would be very difficult to make. You could possibly modify a cathode ray tube from an old television though...
Is uniform magnetic field really possible
how can use this phenomena practically?
It *used* to be used to make television and computer screens. The beam would be scanned across a phosphor screen to generate images. I think electron beams are also used to process materials, like annealing metals.
This is also how x-rays are generated for medical imaging: when a beam like this crashes into a metal and stops, the energy is released as x-rays.
It's also how we use particle therapy in the field of cancer treatment. Using magnets to bend, steer, and focus the beam into the room that is requiring treatment at the time.
sir whats ur mail id?
wwwoooooooowwwww only physics enthusiasts watch this
Pretty obvious basic stuff
Yep, my entire channel is intro physics. :)
still mind blowing though
What then, do you consider non basic stuff?
Show yourself manipulating the power supply, otherwise this appears to be a fraudulent video.
Yes, at 0:33 I increase the bias to increase the intensity of the beam to make it visible. At 1:29 I increase the current in the coils to create the magnetic field that causes the beam to curve. Do you mean you want me to show my hand turning the knobs? But how will you know that they are really hooked up to anything? And if I showed them hooked up, couldn't I fake it by altering the circuitry inside the power supplies? My point is that anything we put in a video someone could claim is fake, so we just focus on teaching the physics content. Peace.
@@Prof-Hafner Champion physicist and professor, great response to a dumb , paranoid comment.