Magnetic field "lines" confused with magnetic field "vectors"

• magnetics
In summary: At the ends of the magnet, the vectors no longer point in opposite directions and the sum of the vectors is zero.
magnetics
Gold Member
I might be a slow learner, but am still trying to understand the difference between field lines and vectors.

I've got that magnetic field lines are symbolic and that the directional arrows applied (from north to south) are a convention.

But see the attached image. The field lines form a closed loop and while within the north pole point in the same direction as the magnetic field vector. But while in the south pole of the magnet, the direction of the field line, is in the opposite direction of the field vector.

Assuming my descriptions are correct, what does this tell us about the convention of magnetic field lines and field vectors?

Thank you.

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magnetics said:
But while in the south pole of the magnet, the direction of the field line, is in the opposite direction of the field vector
No. Both go from norh to south

Not exactly sure what you mean BvU.
So would that mean my diagram is incorrect and if so do the magnetic field vectors from the north and south pole both point in the same direction or do the magnetic field lines change direction somehow when shown inside one half of the magnet??
TIA.

The magnetic field vector at the south pole is drawn the wrong way. It should enter the magnet.

Thanks nasu.
Does that mean the direction for the red magnetic field vector, which we call the south pole should be flipped 180 degrees? That would mean it's pointing in the same direction as the blue north pole, you sure this is correct?

Basically a line only has direction. A vector has direction and magnitude. The magnitude corresponds to the density of the lines in a region. The directions are the same - why would they not be as they correspond to the path that an 'isolated N pole' would take?

magnetics said:
Thanks nasu.
Does that mean the direction for the red magnetic field vector, which we call the south pole should be flipped 180 degrees? That would mean it's pointing in the same direction as the blue north pole, you sure this is correct?
Yes, the arrow at the south pole is in the wrong direction. The arrows on the lines simply show the direction of a magnetic field vector tangent to the line for any point on the line.

jtbell
Thank you for your input, I can see where my misunderstanding is derived. Thanks for the image robphy, I got my own compass and magnets out and indeed the direction of the field lines go in the one direction. Iv'e drawn the field lines correctly, but it seems not the magnetic field vectors. But that now introduces a new misunderstanding hopefully you can help me with.

Sliding a paper clip along a bar magnet and it's obvious there's very little magnetic force in the middle, while it's strongest at the ends. My understanding was that the magnetic field vectors for the domains in a ferromagnetic material would point in opposite directions in the north and south pole. This would explain why adding the vectors from the domains close to the middle of the magnet would summate to zero, hence why there's so little force detected there. While at the ends, the poles are sufficiently separated so as to not influence each other.

Obviously this is not the case, hopefully someone can provide a proper explanation? TIA.

1. What is the difference between magnetic field lines and magnetic field vectors?

Magnetic field lines and magnetic field vectors are often confused, but they represent different aspects of the same phenomenon. Magnetic field lines are imaginary lines that show the direction of the magnetic field at a given point. Magnetic field vectors, on the other hand, are mathematical quantities that represent the strength and direction of the magnetic field at a specific point. In short, magnetic field lines are a visual representation, while magnetic field vectors are a numerical representation.

2. How are magnetic field lines and magnetic field vectors related?

Magnetic field lines and magnetic field vectors are closely related because they both describe the same physical quantity - the magnetic field. Magnetic field lines are used to visualize the direction of the magnetic field, while magnetic field vectors provide a more precise and quantitative description of the field at a specific point. In other words, magnetic field lines give us a general idea of the magnetic field's direction, while magnetic field vectors give us a more detailed understanding of its strength and direction.

3. Can magnetic field lines cross each other?

No, magnetic field lines cannot cross each other. This is because magnetic field lines represent the direction of the magnetic field at a given point, and two different directions cannot exist at the same point. If magnetic field lines were to cross, it would imply that the magnetic field has two different directions at that point, which is not possible.

4. How are magnetic field lines and electric field lines different?

Magnetic field lines and electric field lines are different because they represent two different types of fields. Magnetic field lines represent the direction of the magnetic field, while electric field lines represent the direction of the electric field. Additionally, magnetic field lines form closed loops, while electric field lines start and end on charges. In other words, magnetic field lines are always continuous, while electric field lines can start and end at different points.

5. How can I visualize magnetic field lines?

The best way to visualize magnetic field lines is to use a compass. A compass needle aligns with the direction of the magnetic field at a given point, allowing you to trace out the magnetic field lines. You can also use iron filings on a sheet of paper placed over a magnet to visualize the magnetic field lines. The iron filings will align with the magnetic field lines, giving you a visual representation of the field's direction and strength.

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