Magnetic force on a proton example (part 1) | Physics

Magnetic force on a proton example (part 1) | Physics | Khan Academy

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16 жыл бұрын

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Sal does an example problem to determine the size and direction of the magnetic force on a proton moving through a magnetic field. Created by Sal Khan.
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Пікірлер: 83

@Michael-ur4gd 9 жыл бұрын

"And my hand is brown" lmaooo idk why I laughed so hard at this

@leftysg18 11 жыл бұрын

As a physics teacher I will say...you draw a mean right hand rule

@Rockswamp28 7 жыл бұрын

If you have a TI-84 Plus CE calculator you have to follow a different sequence of buttons to get the charge of an elementary particle: on -> apps -> 0: SciTools -> enter -> 2: Unit Converter -> CONSTANT -> e- -> EXPT -> 2nd -> quit -> 2nd -> quit -> 2nd -> quit

@MBC022 14 жыл бұрын

well this beats having to read the book lol great videos!!

@mrhansenable 13 жыл бұрын

"how does that magnetic field know how fast you're going?" you just blew my mind !

@Nadhy 2 жыл бұрын

Thank you so much for this video - but just wondering, is the force generated always equal to the force required to keep it moving in a circle?

@cvhashim 10 жыл бұрын

I use the very bad finger, VBF. V is your thumb, B is your index finger, and F is your middle finger. Much easier to move your hand in motion.

@Joeylumadip 13 жыл бұрын

I believe using the right hand rule with the thumb representing the direction of velocity, your fingers as the direction of the magnetic field (magnetic field lines) and the force direction coming out of the palm of your hand would be different from the direction of the force which you determined was coming towards us. The right hand rule applies to an electron but when you use a proton, the direction of the force is determined by using your left hand or by using the back of your hand.

@jpjpjpjpx 11 жыл бұрын

Great explanation

@bombardo12 12 жыл бұрын

I find it easier to use my thumb for the velocity, my other four fingers for the direction of the magnetic field and whatever way my palm is facing is the direction of the force

@AndyU96 8 жыл бұрын

+Nick Cruz You can do it with your feet if you wish, as long as you get the correct results, use whatever method you wish that always gives the correct answer. It's like the division "1/0.5", you can either do it with your mind, and realize that there are 2 0.5s in 1, or you can do some algebra and let 1/0.5 = x, and then try to solve it, OR you can view that as (d(x)/dx)/(d(0.5x)/dx), "dx" being "the difference/change of 'x'".

@biotch77 11 жыл бұрын

sal, do you ever get angry? your so calm and easygoing about some hard subjects. :)

@chorcor888 8 жыл бұрын

simply awesome

@jackwilliam2226 Жыл бұрын

A moving proton is in the direction of conventional current, so yes, the force on it would be downwards and clockwise. Electrons move in the opposite direction of the electric field, as well as conventional current.

@Imafungi123 11 жыл бұрын

towards the end, for example at 10:42 you can see the pink magnetic field and the orange charge, and its path... if the charge entered the field at exactly the middle of the field ( in your diagram it is slightly "above" middle.. would it have a different effect, maybe not spinning off to a side at all? or is the point, and why you showed it as you did, that there can never be a perfect middle and the moment there is any more to one side that is the direction it will curve too..

@aznwilly211 13 жыл бұрын

how do you arrange your hand like that???

@HotPepperLala 14 жыл бұрын

I just broke my fingers lol

@stanvideo 15 жыл бұрын

Very, very helpful. Helped me in my physics class. Thank you.

@narayanastudent9392 2 жыл бұрын

hlo

@Fandikusnadi1979 Жыл бұрын

Thank you Khan.

@Acidoverwrite 3 жыл бұрын

Would I need a positive or negative magnetic field in order to fire protons from hydrogen gas towards an object?

@boomit666 11 жыл бұрын

left hand is for electrons , the right hand is for Protons and Ampere measurements.

@grariee 3 жыл бұрын

hey im confused , at 2:01 sal mentioned moving protons at a certain velocity . i dont get it , protons cant move right ?

@MRJerrod410 15 жыл бұрын

Is there an explanation for why a magnetic field exerts a force perpendicular to the velocity of the charge?

@nikex2010 12 жыл бұрын

you say that this is the right hand rule, but isn't the rule the fleming's left hand rule? Or is this another hand rule, and if yes then when do you use that one?

@seanbullis3364 11 жыл бұрын

but the magnetic field is pushing in a specific direction and the velocity is in a specific direction, if the direction of v or the direction of B were changed the direction of the force produced would change too.

@bombardo12 12 жыл бұрын

@couscousable left hand rule works if it the charge is negative

@tnguyen603 16 жыл бұрын

nicely done!! even though I know much of this already!!

@narayanastudent9392 2 жыл бұрын

hlooo

@jbreezena2503 Жыл бұрын

Very good sir

@mortalterminus 12 жыл бұрын

"My finger is brown, so..." LOL!

@MrTroy354 12 жыл бұрын

@qanniee left hand is for electrons, right hand is for protons and amps(current). i dont know what else there is but just remember left hand is only for electrons

@jimmyti9cer 12 жыл бұрын

I am charged! I LOVE PHYSICS!!!

@catherinefernandez9654 2 жыл бұрын

Is that and flemings left hand rule similar? I didn’t understand flemings left hand rule properly, but i remember 2 hand stuff (the other being right hand thumb rule).

@blorb112 7 жыл бұрын

This is gonna sound whack but here me out...Could 'undefined' matter exist in some kind of harmony in some kind of 'field'... until it gains enough mass and slows down to < the speed of light when it is conveyed into the physical world and is reconstituted into the laws of relativity and quantum mechanics.

@andrewjustin256 8 ай бұрын

Hey Mr. Sal. We know from the Special Relativity that magnetic force or field is just electric force ir field viewed from a different perspective. Then the magnetic force on a moving charge is just electric field, right? Please clarify this to me. Also why is the equation only described when there is a in-motion charge? How can I calculate the force exerted by two magnets on each other? Is there an equation for that or is it only depicted by the magnetic field strength (tesla)?

@nhmllr725 13 жыл бұрын

@asetenta But it's not symmetric- the vectors are moving out at us, the south ends go behind the plane of he screen and the north in front.

@ellieuk2002 15 жыл бұрын

Hi.. either i am being totally dumb.. but shouldn't you use the left hand rule? The proton is positive, therefore using conventional current. Thumb = force, index = field, and second = current. Using left hand rule, index fingre points out the page, second finger to the right, and force down...?

@fleshcookie 10 жыл бұрын

Sal's a bomb ass drawer

@thunderboltkrish 11 жыл бұрын

Why doesnt sin(theta) change?Then how can magnitude of force remain constant?The velocity is changing direction while going in a circle?

@blorb112 7 жыл бұрын

It almost seems like on a quantum scale the laws electromagnetism abides by, are different in nature and design to relativity. Like when the mass of a object becomes too great for the electromagnetic field to influence... The force of gravity will intervene on any object.

@ajskilton 14 жыл бұрын

it's the only language for physics we have and I can tell you that Salman makes this very clear if you understand basic vectors otherwise it's like trying to make a sandwich without bread!! tip, 'go buy some bread!'

@BloodyOathMate11 12 жыл бұрын

Im from australia and we use the beautiful metric system..

@j0mezzy 8 жыл бұрын

I guess if it were an electron , we would use the "left" hand rule .... since it would be -Q , and we would have a -F answer meaning negative force

@lawrencejoshuasuarez4321 7 жыл бұрын

Jomel Sagsagat no you will not get a negative force because the charge in the formula have an absolute value

@VivekYadav-ds8oz 5 жыл бұрын

@@lawrencejoshuasuarez4321 he's talking about the direction

@lalalanding234 Жыл бұрын

9:32 Why is force always perpendicular?

@QadeemSamir 12 жыл бұрын

@jimmyti9cer for me, this is standard grade 12 physics

@AnnManMS 15 жыл бұрын

Force is the cross product of the velocity and the magnetic field and is perpendicular to both of them. This comes from the definition of the cross product.

@qanniee 12 жыл бұрын

@MrTroy354 Thanks, I get it now, I appreciate your reply

@gagikRLHS 13 жыл бұрын

10Q very much

@tomascancelliere4348 10 ай бұрын

Right hand rule confuses me. I use index finger for the magnetic field. I see it represented both ways though. Could anyone clarify why it is taught both ways?

@dzMonsterr23 12 жыл бұрын

just do v is the middle finger, palm is in or out, and thumb is b. its a lot easier

@qanniee 12 жыл бұрын

Precise question; when do you apply Left hand rule, and when right hand rule?

@TrailBlazinMan90 4 жыл бұрын

Quratulaain Annie left hand rule when the particle is negatively charged, like an electron. RHR when positive, like a proton

@speedlord2 12 жыл бұрын

Easier Right hand rule: Thumb points with the direction of velocity or current, the rest of fingers point with the direction of the magnetic field. Your palm will point with the direction of force (downward in this case.) [:))]

@InternetDarkLord 3 жыл бұрын

10:05 Einstein called quantum mechanics "spooky at a distance" so you're in good company.

@jimmyti9cer 12 жыл бұрын

@igankyoumaybe no, you may learn this in college fundamental physics courses, this is class you take after you have had two or three calculus classes. Now an advanced placement class in some high schools may offer this level of physics but most dont, I know my high school didnt even for people that were really good in calc.

@j0mezzy 8 жыл бұрын

So the proton doesn't shoot straight back out? It moves in a circle due to the external magnetic field weird...

@ahmadkhalifa5743 11 жыл бұрын

plz reply to me as this is very urgent, i have an admission test soon and there are some questions i nthe sample exam that i don't understand, would u care to help me? it's only mcq :(

@JordanMetroidManiac 9 жыл бұрын

4:42 "multipie" lol

@Representt 13 жыл бұрын

10:25 - 10:39 Possibly Newton's third law?

@PopulistDavid05401 4 жыл бұрын

Spheretext

@asarj24 4 жыл бұрын

@silenttreatment4459 5 жыл бұрын

7:54 Made my day!!!!

@luvlycokee3 12 жыл бұрын

I don't get it

@parthmistry8628 8 жыл бұрын

is this a real calculator or a software?

@silenttreatment4459 5 жыл бұрын

Software. But, there is a real calculator like this one as well.

@MisterTutor2010 12 жыл бұрын

i (negative = left and positive = right) j (negative = towards the reader [out of the paper], positive = away from the reader [into the paper]) k (negative = down and positive = up) Therefore the veactors are: V = 60000000i+0j+0k B = 0i+0.5j+0k Therefore: VxB = 0i+0j+30000000k F = q*VxB = (1.6x10^-19 C)*(0i+0j+30000000k) = 0i+0j+(4.8x10^-12 N)k Because the k component is postive the direction of force must be up.

@Fr4NCHILE 10 жыл бұрын

My teacher taught me the hand rule on the left :x not right So the thumb points the other way :x?

@Rockswamp28 7 жыл бұрын

You use the hand rule for both hands: left hand for negatively charged particles (electrons) and right hand for positively charged particles (protons).

@manudhan 13 жыл бұрын

i think this is wrong cuz thumb is ur velocity, and inderx finger is the magnetic field, and middle finger is the froce, so if we do this question according to this then our force willl go up not down

@Drredfrizzle 11 жыл бұрын

isn't this flemings left hand rule ?

@Mykalpaca 7 жыл бұрын

Drredfrizzle no, left hand ryle is for induced electric currents, right hand rule is for force

@Vanessa-zi4og 7 жыл бұрын

Michael Leung ?? But I thought Left hand rule is used to find force? The right hand rule is used to find Induced current.. 😅😅😅 Ok, I am confused now...

@ShivamPatel-hl9ys 3 жыл бұрын

This won't even be on the SAT physics exam right cause you need a calculator

@Joeylumadip 13 жыл бұрын

Sorry didn't have space. But if any want to comment on this or prove me wrong you can. What I determine is that the direction of the force will go up. So as you see the screen, it would appear the force would go away from you or towards the ceiling.