Magnetic flux density measured for beginners: from fizzics.org

[@shaynomyte90]

This is one of best explanation I have seen in a physics video. Its like you knew exactly what I didn't understand and explained it. The experiment with the coil and the scales is brilliant. I really wish they did that in my physics labs. Cant thank you enough for such a great video.

[@fizzicsorg]

That is a very kind comment. Thank you

[@claude77573]

At 1:39, there is a slide that mentions that the magnetic fields in opposite direction above the wire cancel out and the magnetic fields below the wire reinforce. Well, I have a different thought. Look at the flux lines of the magnet. They are designated as flowing from N to S. If we look at the clockwise flux lines of the wire, and using the same notation the flux flows from N to S, we see that at the top of the wire, the N polarity generated by the wire is on the Left (which is aligned with the South Magnet), and the S polarity is on the Right (which is aligned with the N magnet). As we know with magnetics, opposite polarities attract, so at the top of the wire, the wire is attracted upward. Looking at the bottom of the wire, the N polarity is on the right, and the S polarity is on the left. Since N-N and S-S magnetic polarities repel, there is a repulsion or an upward push on the bottom of the wire.

[@fizzicsorg]

Hi, this is an interesting series of thoughts but you say that "the N polarity generated by the wire" and there is no N generated, it is a circular field. Whichever argument is used it is a way of visualising the explanation of what happens.

[@jaospinam]

Is this James May teaching us? How remarkable his voice resembles May's. Thank you for the lecture!

[@fizzicsorg]

In some ways similar, but much better looking.

[@chbonnici]

This is practical physics at it's best . Well done. God bless you

[@fizzicsorg]

Thank you

[@catmom2509]

Thank you sir for the fantastic demonstration. It all makes sense to me now. Usually this is taught by just working out some equations and a few drawings (if even that) which is too abstract for me.

[@h7opolo]

Your conclusion is correct regarding the direction of emf according to Fleming's left hand rule for motors. Thanks.

[@robertonogueira9874]

WOW. Excelent. I've never seen so perfect explanation. Congratulations, Mr Roger.

[@fizzicsorg]

Thank you, I'm pleased that this was useful.

[@aniani135]

This video was so useful. Specially a week before my Alevel exams.Thank you so much

[@fizzicsorg]

That's great to hear. Thank you and good luck.

[@hardcoremc7053]

Very effective demonstration

[@drewmutt]

Fantastically concise demonstration! Thanks for saving me weeks on Wikipedia!

[@fizzicsorg]

Thank you, it's great you found it useful.

[@cet_learning]

Excellent ... the way you demonstrated how we can work it out from first principles. Best way to learn how stuff works ... thank you for teaching us " how to fish" ... !!

[@fizzicsorg]

Thank you

[@fizzicsorg]

Thank you

[@Ciclify]

Great demonstration!

[@fizzicsorg]

Thank you. I hope it was useful.

[@ally4486]

Thankyou so much . This is one of the best videos I have ever seen on Magnetism, and I understood every part you said . 😃😃😃.

[@fizzicsorg]

A very kind remark, thank you. I am pleased it is useful

[@ally4486]

+Roger Linsell please keep making videos like these Sir . You are helping a lot of people .😊

[@andrefu4166]

extremely helpful thank you

[@fwta183]

I always finds that there are too many unknowns in my equation and can't figure out the sort after Magnetic field, B. Your video is informative and answers a few of my questions. Thanks a lot.

[@SmokyFolk]

this ain't it chief

[@h7opolo]

Well done, sir.

[@marwansallouta2101]

Excellent explanation, thank you. Correction: the length of the wire within the magnetic field is 49 mm = 0.049 m (Not 0.0049 m), so the final answer will be 0.136 Tesla. Great experiment, thank you one more time.

[@blessedwarrior1]

Loved watching every bit of it....♡♡♡

[@fizzicsorg]

Good that it was useful

[@blessedwarrior1]

@@fizzicsorg yep

[@mohammadalshaikhhasan5091]

from my electromechanic engineering book i have another formula used for the force (Mmf , magnetomotive force), as can be seen from bellow page scan from the book. F= ΦR (where Φ is the magnatic flux, and R is the reluctance) Φ = BA R= l/uA (is is the permeability) so F = Bl/u my question, why are the two formulas not matching (the first formula from your youtube, the second formula from the book)? What did I miss and mistaken? F= ΦR (where Φ is the magnatic flux, and R is the reluctance) Φ = BA R= l/uA (is is the permeability) so F = Bl/u my question, why are the two formulas not matching (the first formula from your youtube, the second formula from the book)? What did I miss and mistaken? And i have to thank you for the awesome and informative video

[@itsJeffyy]

What are the independent, dependent and control variables? And how can i minimise uncertainty?

[@alejandroquinones5439]

Awesome! Why is that less N increases B?

[@divvy1400yam600]

Whats the difference between B flux density and H field strength. /

[@mohammadalshaikhhasan5091]

Same question i do have? Did get answers you can share it Thanks

[@divvy1400yam600]

@@mohammadalshaikhhasan5091 yes I believe I do now understand it. (I think)] Note the formula B = mu(0)mu(r)H If a current flows down a long thin wire in FREE space then moving out in circles is a magnetic field This is shown in the vid and is H the field strength Many texts describe that as B but I believe that is wrong and is the root cause of the confusion.. Now no longer in FREE space we have a current flowing then the resultant field is B the flux density, In the the vid this is shown as the fields interacting between the the magnets and the wires. Imagine a rectangle at 90 degrees to B then the magnetic strength through that rectangle is maximum. If the rectangle is at zero degrees then the magnetic effect is zero. ie sin (theta) is involved in working out the strength. sin(0) = 0=zero effect sin(90) =1=maximum effect.

[@chbonnici]

I wish you show us how to make an experiment to plot BH curve of an unknown core. It will be awsome

[@robertonogueira9874]

B = 0,136 T . You used 0,0049 instead 0,049. God Bless you.

[@fizzicsorg]

Absolutely right! Nearly 10,000 views and no one else noticed and neither did I. I have put a note on the frame. Thank you

[@dansshop]

I didn't catch that error, but I did know for sure that 1.36T seemed off by about a factor of 10 given that sort of magnet and the setup. 1.36T would be impossible with any sort of magnetic material in that setup.

[@dansshop]

Oh, and it's an awesome video, thank you!

[@jdtaramona]

Good for you 👏

[@faisal2401]

1:46 could you further explain how the 2 permanent magnets will be pushed on opposite direction?

[@fizzicsorg]

This is just Newton's Third Law. If the wires are pushed up then there has to be an equal and opposite reaction, that is a push downwards. The magnets are therefore pushed down and that extra force downwards is what we measure on the balance.

[@faisal2401]

Roger Linsell i could only imagine that applies on contact forces. i mean physically in contact. but since the wire in middle of the two magnets, i suppose the only reason the magnets being pushed down is due to distortion of magnetic flux. in which i couldn't find any scientific explanation/formula on that

[@fizzicsorg]

No, it applies to any forces. Try getting two magnets and pushing the north poles close together. There is a force on both, equal and in opposite directions.

[@donation1913]

Does the distance between the magnets affect the flux density? If the magnets are closer together do the Teslas increase? Now I have to rethink my Axial Flux calculations with, N x A x T/s = Volts. Will the result from this experiment be used to calculate Faradays Law for a Magnet Moving Past a Coil?

[@nuwankarunaratne6069]

Here in USA Physics undergraduate textbooks does not talk about magnetic flux density, instead we simply call it the magnetic field. Thanks!

[@Waterboy1214]

Fantastic demonstration and lesson!! Thank you! I do have one question though, why is the wire pushed towards the weak magnetic field where the flux fight each other?

[@fizzicsorg]

Because then the very strong field is weakened as the wire moves away leading to a lower energy level. Systems always move to reduce/spread energy out (second law of thermodynamics)

[@Waterboy1214]

Thank you!!

[@abderrahmanezerouali2381]

ROGER please Why opposite magnetic fields in opposite direction cancel out , Do you mean in this case the magnetic field created by current and the other of Magnetic poles , are the result cancel out in all cases , In forces the result and direction of opposite forces is relating to the value of each force how about the magnetic fields ?

[@fizzicsorg]

The strength of a field is a measure of the effect it would have on a "theoretically tiny" magnet inside the field. If there are two fields, one pulling in one direction and another in the opposite direction then they cancel out.

[@4pharaoh]

Question: I'm sure that if you increased the number of wires from 6 to 60 while decreasing the current to a 10th of the original the force would be equal to your original; however, is there a difference in the magnetic fields themselves? Is there 10 times fewer "lines of force" that are 10 time stronger in one configuration over the other for example? Is one "line of force" the same as another? If Two magnetic fields have equal strengths loop over a greater distance, say earths 50 microteslas vs a fridge magnet over a few inches, then what is the difference between the individual "Lines of force?"

[@paryboy94]

When you hit up the switch, what are you turning on? I missed that part. Thenk you!

[@fizzicsorg]

The current through the coil that creates the magnetic flux

[@vikramnain5908]

Great one.... Always

[@fizzicsorg]

Thank you, glad it is useful

[@fardinheidari5787]

thanks. so useful and perfect

[@fizzicsorg]

That's a very nice comment, thank you.

[@vahagnmelikyan2906]

What do you mean by magnetic strength. If more current passes through the wire does it add more magnetic flux lines, or increases the speed of magnetic field particles?

[@fizzicsorg]

Think of it adding more flux lines

[@imranhbagoro]

big thanks for this beautiful video, The setup works similar to "a moving magnet voice coil motor"??? BTW some errors exist in mathematical calculations.

[@fizzicsorg]

Hi, thank you, I think. It does aim to explain the basics of all electro/magnetic devices producing movement. There is a decimal place error, acknowledged in a remark below at 4.34 where I have used 0.0049 instead of 0.049

[@imranhbagoro]

Roger Linsell, what would be the length L in case of a current carrying coil placed between two magnets. In this video, L is considered as the length of the magnet because the wire is straight.

[@fizzicsorg]

@@imranhbagoro If the coil is all within the magnetic field then it is the area of the coil that is key. The emf produced depends upon BAN where B is the magnetic flux density, N the number of turns in the coil and A the area. The emf will rise and fall in a sine curve but the maximum emf will be BAN x omega where omega is the angular velocity.

[@skydronetechnologies2589]

I'm designing a power distribution hub for a large quadcopter using (2) copper washers... One for positive and one for negative. They will be isolated with a rubber gasket and will distribute the power from a 22V power source to the motors. I'm concerned about the magnetic field created by the current and it affecting the flight controller electronics. Specifically, should I cut a slot in the washer to 'break' the loop? So instead of having a circle washer, it will look like a 'C'. Will it help or hinder?

[@fizzicsorg]

hi, I'm no expert on remote control systems but I would not have thought that the field around a single wire or the washer would be significant, particularly since the current will not circle round and around the washer even without a slot.

[@skydronetechnologies2589]

Thanks for responding. The electronics on RC drones is very susceptible to EMI, so I want to minimize. I'm not an electrical engineer, but I was told that having a circle washer vs a "C" shaped washer allowed the electrons to flow in a circular path and could cause more interference. Are you saying the shape of the washer has no bearing on how the electrons flow? BTW, I sent you a friend request so I could send you an actual picture of the power hub.

[@abdellahiabderahmane3731]

Thanks for the great video. I want to know the reason behind the vertical motion of the wire, I understand the magnetic density difference above and under it, but since the wire can be made of non magnetic material (for example copper), what exactly is the force pushing it up ?? is it the Faraday force acting on the electrons. A second question may be more stupid than the first one ;), does the magnets have to be held by a magnetic material ??, it is just difficult for me to apply Newton third law here, in order to understand why we have the motion of the metal brakets. Thank you very much

[@fizzicsorg]

Hi, yes the material of the wire does not matter, mine were copper. The force is caused by interaction between the fields. The field around the wire is caused by moving charge i.e. the electrons within the wire, hence the force on the wire. The brackets used here were iron which increases the strength of the field, but with a bit of glue to hold the magnets in place, other materials could be used.

[@aa5845]

Thanks for the video....

[@lenrd9638]

Thanks for the video. I used your method to measure the field between two N52 magnets (25 mm x 49mm x 10mm) at a gap of about 25 mm and came up with around 0.15 Teslas. However, the calculator at this site: www.kjmagnetics.com/gap.calculator.asp leads me to believe that I should have measured twice that strength. Note that the calculator is set up for disc magnets, so I assumed an intermediate diameter, i.e. 37 mm. My measurement device did not use a steel holder. It was wood, and the magnets were held in place with two thin polycarbonate sheets. I don't think that would have made a difference. Any ideas on the cause of the discrepancy?

[@fizzicsorg]

Hi, sorry I have only just seen your comment which, for some reason, was flagged as unsuitable. However the answer is no, I don't know.

[@AliRaza-wg9pt]

Wow amazing

[@Mejono90]

That was amazing sir thank u🇵🇰

[@fizzicsorg]

Good that it was useful. Thanks for the comment.

[@johncarl8999]

Could you please provide the schematics for this practice?

[@fizzicsorg]

Do you mean a line diagram of the parts?

[@johncarl8999]

Yes. I want to do this experiment. What I mean is if you could provide the diagram, so I will see how did you conected the multimeter and how conected the source to have current in the wire.

[@nidalfikri3445]

awesome ! thank you sir :)

[@fizzicsorg]

Thanks. Good luck in your studies.

[@SoyoungOh-f4q]

How downward force opposite to upward electromagnetic force exist? Electromagnetic force acts on conducting wire. How wire act reaction force to scale?

[@fizzicsorg]

The electromagnetic field which pushes the wire up is the same one that pushes the magnet down, with equal force

[@SoyoungOh-f4q]

​@@fizzicsorg Thank you for answer! But I'm still confused. The electromagnetic force pushes the wire and so the wire makes reaction force down. However the magnets are perfectly away form wire. I think it doesn't have any way to send force wire to magnet. Help me...

[@fizzicsorg]

​@@SoyoungOh-f4q The electromagnetic field around the wire and the field of the fixed magnets act against each other. Think about two permanent magnets with north poles facing. The repulsion is between the two magnets, both are pushed with equal force.

[@hamster-wh3ws]

Very nice.

[@vahagnmelikyan2906]

Would it be possible to create a boat that is being pushed by interaction of earth's magnetic field and a coil magnetic field? I saw a bar magnet lining itself with earth's magnetic field on the surface of water, what will happen if it was a coiled magnet?

[@fizzicsorg]

An attractive idea and maybe you could get a tiny push in one direction. in practice however the Earths magnetic field is very weak and the portable magnet would need to be very strong. You would not be able to avoid the Law of Conservation of Energy, the energy needed to create and turn the magnet around would be greater than that gained.

[@vahagnmelikyan2906]

Roger Linsell but if i was able to make a disc like loop of wires. Basically wire on wire only, it would become a very wide loop covering big surface area and interacting with more of the earth's magnetic field flux lines... like a ufo...

[@fizzicsorg]

Yes, but the larger the area of the coil, the weaker the field the current creates and I think the electrical energy driving a motor would use the energy more efficiently

[@deegee3142]

what about the weight of the magnets and steel bracket?

[@fizzicsorg]

The balance is tared (set at zero) after placing the bracket and magnets so the measurement is of the extra force created by the interaction of the magnetic fields.

[@deegee3142]

of course. cool.

[@myuceer]

So,you are measuring the flux density of the magnet. What about measuring the flux density of the wire?

[@fizzicsorg]

That varies on the inverse of the distance from the centre of the wire/coil and can be calculated from the current and the number of turns.

[@myuceer]

I mean how to measure?

[@fizzicsorg]

Calculate using B = magnetic permeability x current / 2 x pi x radius from centre. Could measure using a Hall effect probe.

[@ABHISHEKKUMAR-hi8hs]

how you mesure value of force. please

[@fizzicsorg]

I think it explains in the video lesson. By weighing the counter balance weights

[@MINHHOANG-hl7gp]

can you tell me why there's a force pushing the magnet downward when there's a force pushing the wire upward ?

[@fizzicsorg]

If there is a force pushing the magnet down then something has to be pushed up to balance that (Newtons third Law) The onlt other component in this demonstration is the wire.

[@ZetaReticulli]

It's still not clear why the forces are resolved along the vertical axis. At 1:47, it is clear that the forces will cancel each other at the top - but I would have thought that the force will accumulate along the horizontal axis (based on the drawing), so I was expecting a left right motion rather than a up down motion. Could you explain why the movement is up down instead of left right?

[@thereynolds2725]

Neil Osborne The force experienced by a current in a magnetic field is at 90 degrees to both the current direction and the external field direction.

[@10bokaj]

are u not missing a mu0??

[@heroldhenry4257]

unit of 0.1361 is tesla? isn't it webers? since T=Wb/m^2 you need area to get tesla...

[@fizzicsorg]

Hi, it is great to see you are thinking this through. You are right that flux density is dependent on area, however, the calculation here is from the value of the force on the wire. The force is dependent flux density not on the total flux so we don't need to take the area into account.

[@heroldhenry4257]

ok thanks.if B=unit tesla then phi=can either stand for magnetic or electric flux. Just want to double check.

[@fizzicsorg]

Hi, sorry I don't understand your question. What are p and h. But in any case one thing cannot represent both magnetic and electric flux.

[@heroldhenry4257]

oh i mean that greek alphabet "phi" a circle and a vertical line right in the middle....

[@fizzicsorg]

Well no, magnetic and electric field strength are dependent upon different conditions.

[@cityzen8539]

how to convert tesla to henry? would it be possible?

[@fizzicsorg]

No, they are used to measure different things

[@nelsonenegbuma6033]

why did you convert mass to 0.020 when calculating the force. The mass value was 20kg which is the SI unit. why F = 0.020 * 9.8 = 0.196N

[@fizzicsorg]

Sorry about the slow reply, I have been away. The mass value is 20g not 20Kg so 20g = 0.020Kg

[@nelsonenegbuma6033]

@@fizzicsorg oh okay. I understand now. I am a graduate student and for my thesis I want to determine the Magnetic and electromagnetic field emission from electric cars. I would love to share my write ups with you for advise if you are open to it. Thank you for responding

[@ssiddiqui7301]

every thing is great but i think that according to right hand rule the north and south are reversed at 0.38 second

[@fizzicsorg]

Hi Summaya. The magnets shown are permanent magnets which I put in place, not a magnetic field created by induction. The field around the wire and the field of the permanent magnets will reinforce below the wire so pushing the wires up and at the same time, pushing the magnets down.

[@ssiddiqui7301]

so do you want to say that magnetic field due to permanent magnet is changed from magnetic field due to current but i want to say that line arises from south but i read that magnetic field lines arises from north to south

[@fizzicsorg]

Check the diagram from 1.32

[@troyw5832]

☺😊😀😁😂5 Smile's ( got a example and constant book in the SL you can learn this in 10min with a example test done correctly like this.)😆

[@kelvinmurimi9179]

Best ever

[@fizzicsorg]

Thank you

[@eelcogg]

Love the explanation, but the constant panning and zooming was really annoying, especially on the equations.

[@TriPham-sn9jj]

A car can be blown away if enough magnetic combined with enought density

[@xJoe90]

I wish you were my teacher

[@fizzicsorg]

Avery nice comment, thank you

[@DeepakKumar-rx2oo]

Concept is very clear but please make vedio in hindi language

[@fizzicsorg]

That would be good, but I cannot speak or understand Hindi. If you, or anyone else, would like to provide a translation to be added with subtitles, that would be great.

[@gabrieldiassoaresfkj4969]

Hello sir can i get your email?

[@veronicanoordzee6440]

For beginners??? Sir, you lost the connection with reality.