magnetic fields Definition and Topics - 29 Discussions

A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. A permanent magnet's magnetic field pulls on ferromagnetic materials such as iron, and attracts or repels other magnets. In addition, a magnetic field that varies with location will exert a force on a range of non-magnetic materials by affecting the motion of their outer atomic electrons. Magnetic fields surround magnetized materials, and are created by electric currents such as those used in electromagnets, and by electric fields varying in time. Since both strength and direction of a magnetic field may vary with location, they are described as a map assigning a vector to each point of space or, more precisely—because of the way the magnetic field transforms under mirror reflection—as a field of pseudovectors.
In electromagnetics, the term "magnetic field" is used for two distinct but closely related vector fields denoted by the symbols B and H. In the International System of Units, H, magnetic field strength, is measured in the SI base units of ampere per meter (A/m). B, magnetic flux density, is measured in tesla (in SI base units: kilogram per second2 per ampere), which is equivalent to newton per meter per ampere. H and B differ in how they account for magnetization. In a vacuum, the two fields are related through the vacuum permeability,







{\displaystyle \mathbf {B} /\mu _{0}=\mathbf {H} }
; but in a magnetized material, the terms differ by the material's magnetization at each point.
Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. Magnetic fields and electric fields are interrelated and are both components of the electromagnetic force, one of the four fundamental forces of nature.
Magnetic fields are used throughout modern technology, particularly in electrical engineering and electromechanics. Rotating magnetic fields are used in both electric motors and generators. The interaction of magnetic fields in electric devices such as transformers is conceptualized and investigated as magnetic circuits. Magnetic forces give information about the charge carriers in a material through the Hall effect. The Earth produces its own magnetic field, which shields the Earth's ozone layer from the solar wind and is important in navigation using a compass.

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  1. Adesh

    Can a magnetic field ever cause a translation motion?

    Lorentz Law says that for a charged particle moving with a velocity v in a magnetic field B then the force on it is given by $$ \mathbf{F} = q (\mathbf{v} \times \mathbf{B}) $$ Now, if I say that particle’s velocity and the magnetic field are aligned then according to Lorentz Law there will be...
  2. S

    How to measure electric and magnetic fields in asymmetric capacitors?

    Summary: I need to build an asymmetric capacitor, but the mathematics of electromagnetics become too tough, do you have any info that can help? Appreciate it!!! Hello, I am an undergraduate student in engineering and I want to build an asymmetric capacitor, so I need electromagnetics which I...
  3. P

    Is there any evolutionary benefit from magnetoreception?

    Some organisms still have magnetoreceptors, what would be the evolutionary benefits of these receptors?
  4. M

    Origins of magnetic fields from permanent static magnets versus current

    The videos from Veritasium explaining permanent static magnets and electromagnets were quite good I thought… But they have me a little confused with regard to the origins of magnetic fields generated by an electric current as opposed to a permanent static magnet from say iron. 1. An...
  5. Boltzman Oscillation

    I What are the consequences to electric and magnetic in GR?

    So I just learned that in general relativity Magnatic and Electric fields are dependent on the observer. What are some consequences as a result?
  6. Robert Friz

    How does a magnetic field collapse?

    I have a basic question about magnetic fields, but the answer will help me better understand quantum collapse issues. If the current in a wire is instantaneously shut off, what happens to the magnetic field that was present when the current was flowing? To be more specific: Wire...
  7. M

    I Relativistic particle in non-uniform magnetic field (math)

    Hi everyone, I am currently working on a project in Physics analyzing the possibility of magnetic fields protecting against radiation particles such as fully ionized nuclei or electrons. I wrote a code in Matlab that simulates a 3-D magnetic field based on a combination of wires and wire loops...
  8. P

    Direction of Magnetic Fields

    Homework Statement How do I find the direction of the magnetic field at the points? Homework Equations Ampere's B = (UI) / (2*pi*r)[/B] The Attempt at a Solution I know how the Right hand rule, where your thumb is the direction of the current and your hand wraps the direction of the...
  9. CricK0es

    Helmholtz Coil

    Homework Statement Hi, I've got a presentation on an experiment we did using the Helmholtz coil and I'm starting to run dry on material. As some additional applications I found that you can: - Use the coil set up to cancel external interference (Shield other experiments? Not sure about that...
  10. dumbdumNotSmart

    Induced current of a coil on another coil

    Homework Statement We have two coils of copper wire, drawn below. One has a battery connected to it. The other one has a galvonometer connected. If the coil with the voltage is moved closer as shown in the picture, with considerable velocity, what direction will the current induced on the other...
  11. joshua cruwys

    Examine the circuit and answer the questions grade 11 physics 1. Homework Statement find the unknown poles, draw the magnetic field around the conductor, and determine the direction of the force acting on the conductor. Homework Equations N/a The Attempt at a Solution...
  12. F

    Non Uniform Magnetostatic fields

    Homework Statement Describe semiquantitatively the motion of an electron under the presence of a constant electric field in the x direction, E =E0x^ and a space varying magnetic field given by B = B0 a(x + z)x^ + B0 [1 + a(x - z)]z^ where Eo, Bo, and a are...
  13. M

    How to calculate force caused by magnets?

    I am trying to calculate the forces between a simple sphere neodymium magnet on other iron surfaces and magnets. I did a lot of research but still not sure what equation to use or how to apply them. I found the following equations here ( F =...
  14. Quadrat

    Electron passing through a magnetic and an electric field

    Homework Statement An electron with velocity ##\vec{v}_0=8.7*10^4(m/s)## (in the î direction) passing through an area with a uniform magnetic field ##\vec{B}=0.80 T## (in the negative k̂ direction). There's also a uniform electric field in this area. What is the magnitude and direction of...
  15. Quadrat

    Induced emf in various rectangular loops

    Homework Statement [/B] Three conducting loops, all with the same resistance ##R## move towards a uniform and constant magnetic field, all with the same velocity ##v##. Their relative sizes can be identified by the grid. As the loops move into the magnetic field an induced current begins to...
  16. Mohummed Kazmi

    Negative values of magnetic fields strength obtained?

    Homework Statement We were asked to use a Hall probe (in units of Guass) to measure the magnetic field strength in 0.5 cm increments away from a wire carrying 4 A of current. As we got further and further away from the wire our B value got smaller and smaller. Eventually they became negative...
  17. Lee power

    Chemical reaction metal underwater

    Hi guys I was wondering of someone on here could briefly enlighten me on the chemical reactions that would occur with a Teflon Coated high carbon steel hook and a lead sinker while underwater? I am looking into the signals that may or may not be given off by these items both separately and with...
  18. X

    Looking for material with specific magnetic properties

    Hi, To begin with, I am not a native English speaker and have very limited knowledge regarding magnetic fields and thus want to apologize in advance for probable use of incorrect terms. http:// In the picture above, M represents a magnet. S is a material that is not allowed to be affected...
  19. V

    Direction of current in a magnetic field when loop is square

    Homework Statement A flexible wire loop has a radius of r = 0.178 m and it is inside a uniform magnetic field of B = 0.332 T. The loop is grasped at points P and Q and stretched until its area is zero. It takes 0.146 s to close the loop. Homework Equations EMF = ∆Phi/∆t Phi = magnetic flux...
  20. ulfurh

    Help with electromagnetic musical instrument design

    Hello everyone, For the past 4 years I have been working on a new type of musical instrument that fuses together elements from electronic music into the acoustic realm. The instrument consists of 26 strings inside a wooden enclosure that are actuated (or "bowed") by the use of electromagnets...
  21. R

    How would one describe the universe in which

    there are no electromagnetic waves? All I know is that there is a modified version of the Maxwell equations (in differential form) for such a universe, such as (the arrows represent vector arrows): →∇x →B = μ0 →j + μ0 ε0 ∂→B/∂t instead of having ∂E/dt in the last term (which would be the case...
  22. Roy Stout

    Charged particles passing through a magnetic wave?

    Random thought... Is it possible for a charged particle to travel fast enough, or simply enter a magnetic field at just the right time in the magnetic wave's cycle, to pass through the magnetic field unaffected? If so, what is that calculation. If not, why not. Roy
  23. A

    A circular loop over a magnetic field directed outwards

    Homework Statement There is a counterclockwise current I in a circular loop of wire situated in an external magnetic field directed out of the page as shown. The effect of the forces that act on this current is to make the loop Select one: a. expand in size X b. contract in size c...
  24. Z

    Will electron create gamma-radiation?

    If we put cathode rod with enormouse voltage in vacuum between strong magnetic fields pointing down paralel to rod end then put electron in it with initial speed equal to speed of light and begin circling around cathode, Will electron make gamma -rays according to synchrotron radiation?
  25. A

    Where is North, given this current?

    Homework Statement Copy the diagrams in Figure 7 into your notebook, and draw the direction of the conventional current or the magnetic field lines. Also indicate the location of the north and south poles where appropriate. FIGURE 1 FIGURE 2 Homework Equations The Attempt at a Solution...
  26. S

    Curl of Z-unit vector in spherical coordinates

    Homework Statement There is a sphere of magnetic material in a uniform magnetic field \vec H_0=H_0\vec a_z, and after some calculations I got the magnetic moment vector \vec M_0=M_0\vec a_z, where M_0 is something that isnt important to my question. I am unsure if this magnetic moment vector...
  27. gauss44

    Do magnetic fields tend to align? (moving charge & other B)

    When a moving proton travels through a magnetic field, doe's it's magnetic field (that it's giving off) naturally align with the outside magnetic field (due to a magnet or something in the environment)?
  28. G

    Finding the magnetic field of an infinite cylindrical wire.

    Homework Statement An infinite cylindrical wire of radius ##R## carries a current per unit area ##\vec{J}## which varies with the distance from the axis as ##J(s)=ks^2\hat{z}## for ##0<s<R## and zero otherwise where k is a constant. Find the magnetic field ##\vec{B(s)}## in all space. Homework...
  29. M

    Finding the magnetization vector and magnetic field?

    Hello, I've been stuck on this question for a few hours and I hope someone can help. Here is the question: "Consider two materials bismuth and aluminum with χ m = −20 ×10−5 and χ m = 2 ×10−5, respectively. Find the magnetization vector and the magnetic field in these materials when they are...