Question

The difference between 1) Uniform magnetic field
2) Non-uniform magnetic field

Can anyone simply give me the difference? Stating a simple example would be nice, thanks!

Answer 1

A uniform magnetic field doesn't depend on position, its the same everywhere. A non uniform magnetic field changes from one place to another.

The electric field inside the plates of a large parallel plate capacitor is uniform, the field is the same size and points the same direction everywhere in between the plates. The electric field of a point charge is non-uniform, it points in a different direction everywhere
in space, and gets smaller as you move further away from the charge.

The magnetic field produced by a pair of Helmholtz coils is approximately uniform in between the coils, while the magnetic field produced by a long straight wire is non-uniform.

Answer 2

@fwizbang , I found this over @ wikipedia. Could you simply describe it for me?

"For if a magnet is placed in a uniform magnetic field then both poles will feel the same magnetic force but in opposite directions, since they have opposite magnetic charge. But, when a magnet is placed in the non-uniform field, such as that due to another magnet, the pole experiencing the large magnetic field will experience the large force and there will be a net force on the magnet. If the magnet is aligned with the magnetic field, corresponding to two magnets oriented in the same direction near the poles, then it will be drawn into the larger magnetic field. If it is oppositely aligned, such as the case of two magnets with like poles facing each other, then the magnet will be repelled from the region of higher magnetic field."


I honestly DO NOT! understand whats going on here... Can anyone help me out?
Thanks!

Answer 3

In this case Wikipedia's description is wrong. If you changed the word magnetic to electric, this would be a reasonable description of what happens to an electric dipole in an electric field, since electric dipoles can be thougt of as having opposite charges on either end. Magnets are (often)magnetic dipoles,
but you can't think of them this way because there is no such thing as magnetic charge.(At least nobody has found one yet.)

The cleanest way to think about this(at least to me) is to think about the magnetic field energy, which is
\[\int\limits_{?}^{?} {B _{tot }^2\over 2\mu_0} dV\]

The magnetic field has two contributions, one from the "external" field \[ B_{ext} \] and the other the field produced by the magnet itself, \[ B_{mag} \].

The integrand in the magnetic field energy will have three terms. One will just be an integral over the external field, one just over the field produced by the magnet, and then there will be a cross term that involves both. When the magnet moves, it minimizes the integral of the cross term and lowers the total field energy. Since energy is conserved, this energy reappears as the kinetic energy of the magnet.

Answer 4

@fwizbang
I think the text ment a charge with a magnetic field maybe?

What I've understood from that text is an example of a magnet in a uniform(=) field and a non-uniform(not equal) field. And what would happen to that magnet during those states, a stronger field will exert a stronger attraction/repelling force. A weaker field would do the opposite.

That what I've pretty much understood when I read it again.

Answer 5

Its a very confusing matter to study about :s

I just wanted to find out the magnetic forces exerted on a magnet when being attracted/repelled by another magnetic field example: 2 bar magnets attracting/repelling each other.

It obviously depends on many many many! Factors that I find difficult to calculate.
However, that text merrily shows how magnets interact in a weaker/stronger magnetic field. If its within a strong one a strong force is generated, if a weaker one a weak force is generated (Correct me if I'm wrong!).

Answer 6

How is it possibile to calculate magnetic force exerted on magnets?

Answer 7

Just like a loop of wire feeling the same force. Magnetic force!

Answer 8

if the field strength of induction is same at every point in both magnitude and direction is called uniform magnetic field. in uniform magnetic field the lines of force are straghit parallel and equidistant.

Answer 9

@nitinz570 Ow, so if for example the magnitude is not the same but the direction is or viceversa the magnetic filed is not a uniform one? For example a inductor's magnetic field is stronger then a permanent magnet's = non uniform?

Answer 10

I'm staring to get this :)

Answer 11

In most cases, calculating the magnetic force on a permanent magnet(or the field
produced by a permanent magnet0 isn't done in introductory E&M because the math required is too difficult. Typically, it is covered in the Junior Level courses in books
like Griffiths or Jackson.

Answer 12

@fwizbang
Ok but,

Do you agree that:
1)for example the magnitude is not the same but the direction is or viceversa the magnetic filed is not a uniform one? For example a inductor's magnetic field is stronger then a permanent magnet's but the same direction= non uniform?

2) If a magnet is in a strong magnetic field strong force is generated, if a weaker one a weak force is generated (Correct me if I'm wrong!). + What can I specifically study to prove that point?

Answer 13

@Jemurray3 need you're help once more!

Answer 14

The thing is calculating the magnetic force is really complicated business. I don't really know where to start exactly. :S

Answer 15

Can anyone answer this for me

Do you agree that:
1)for example the magnitude is not the same but the direction is or viceversa the magnetic filed is not a uniform one? For example a inductor's magnetic field is stronger then a permanent magnet's but the same direction= non uniform?

2) If a magnet is in a strong magnetic field strong force is generated, if a weaker one a weak force is generated (Correct me if I'm wrong!).

+ What can I specifically study to prove that point?

Answer 16

Thanks @85295james :)

Answer 17

Do you have any contributions about this topic :D @85295james ?

Answer 18

no sorry

Answer 19

Ow,ok. Thanks anyway!

Answer 20

your welcome

Answer 21

@fwizbang need you're opinion on this:

Do you agree that:
1)for example the magnitude is not the same but the direction is or viceversa the magnetic filed is not a uniform one? For example a inductor's magnetic field is stronger then a permanent magnet's but the same direction= non uniform?

2) If a magnet is in a strong magnetic field strong force is generated, if a weaker one a weak force is generated (Correct me if I'm wrong!).

+ What can I specifically study to prove that point?

Answer 22

Uniform means the same. In physics, we usually use uniform to mean something that doesn't change when you change location and constant to indicate something that doesn't change with time. Since a magnetic field is a vector field it can only be uniform
if it is the same magnitude(size) and points in the same direction at all places in the region in question.

There is only a force on the magnet if it is in a non-uniform magnetic field, regardless of the magnitude of that field. So, for example, small magnets do not spontaneously move their Center of Mass in the Earth's magnetic field, which is pretty uniform over regions the size of the magnet. Like I said, this kind of question is usually not dealt with at the introductory level(College or HS physics), but is covered in more advanced treatments of Magnetism in texts like the ones by Griffiths or Jackson.

Answer 23

Can a magnet for example ever be a non-uniform? In some cause or situation/circumstances?

If for example we brought 2 magnetic object's of different fields and same size's. Let's say a magnet and a electromagnet. If the magnet is placed within that electromagnet's field that is different. This is a non-uniform situation right? True that its a vector. But as you said "the same" if one vector is higher then the other surly it's not a uniform one yes?

Answer 24

@lgbasallote @experimentX @.Sam. @dpaInc Help!

Answer 25

The thing I want to state out is fo example: When a magnet is placed in a moveable state and a object experiences that magnetic field from the magnet. As the magnet moves! Its field changes thus the magnetic field of the magnet is non-uniform.

Another example is the weaker/stronger magnetic field's stated above being a uniform one and a non-uniform one...

I'm I in the right track here or I got this all wrong? Hope someone could give me an example of uniform and non-uniform magnetic fields if I got my examples wrong... Thanks!

Answer 26

perhaps ... you are right!!
the different flux density gives non uniform magnetic field.

Answer 27

Yes!!
I was thinking about this for so so long! Thanks @experimentX !
What a relief...

Answer 28

don't be so sure ... I'm not pretty sure about it myself. can we discuss this later ??

Answer 29

Sure! Just come back please to help me out! :)

Answer 30

sure ...!!

Answer 31

In the situation you describe, the magnetic field is neither constant nor uniform.
It.s not uniform because, as the magnet moves, the field it produces at locations
that surround it varies with time.

It's not uniform because the magnetic field gets weaker as you consider points that are further away from the magnet. It's also not uniform because the magnetic field lines curve around the magnet and eventually close on themselves, which they must do as there are no magnetic charges for the field lines to start or end on. In fact, magnetic fields are never perfectly uniform, as they must always close back on themselves.

Answer 32

Thanks @fwizbang that clears things out perfectly.

Now it safe to say in my condition that I've stated the magnetic field is a "non-uniform" one.

Answer 33

Since its not constant I feel the magnetic field's of both magnets will interact and a net force will be produced. So the statement that I've used before fit this perfectly dosen't it :) @fwizbang ?

Answer 34

Yea I think this question is answered pretty well. Thanks everyone!

Answer 35

@fwizbang just to add a point and example:

Bring an electromagnet and a permanent magnet.

An electromagnet's magnetic field strength,density is more of the magnet. So in this case "again" the magnetic field generated by the electromagnet is a non-uniform one.

The magnet will accelerate based on the force generated by that non-uniform magnetic field from the electromagnet.
The resembles a motor being controlled by a "speed controller". When you increase the input you also increase the magnetic field/force and that would lead to a non-uniform magnetic field that would create a significant force to that permanent magnet(stator) and would generate torque.

I've tried this experiment multiple times and the results were amazing :)