Magnetic force Definition and 416 Threads

In physics (specifically in electromagnetism) the Lorentz force (or electromagnetic force) is the combination of electric and magnetic force on a point charge due to electromagnetic fields. A particle of charge q moving with a velocity v in an electric field E and a magnetic field B experiences a force of





F

=
q


E

+
q


v

×

B



{\displaystyle \mathbf {F} =q\,\mathbf {E} +q\,\mathbf {v} \times \mathbf {B} }
(in SI units). It says that the electromagnetic force on a charge q is a combination of a force in the direction of the electric field E proportional to the magnitude of the field and the quantity of charge, and a force at right angles to the magnetic field B and the velocity v of the charge, proportional to the magnitude of the field, the charge, and the velocity. Variations on this basic formula describe the magnetic force on a current-carrying wire (sometimes called Laplace force), the electromotive force in a wire loop moving through a magnetic field (an aspect of Faraday's law of induction), and the force on a moving charged particle.
Historians suggest that the law is implicit in a paper by James Clerk Maxwell, published in 1865. Hendrik Lorentz arrived at a complete derivation in 1895, identifying the contribution of the electric force a few years after Oliver Heaviside correctly identified the contribution of the magnetic force.

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  1. B

    What is the relationship between magnetic force and electric force?

    Noob, apologies to all. What is magnetic force? I can calculate it, and know that it is perpendicular to the motion of an electric force, but what is it? Just because I can calculate it does not mean that I know what I am calculating. Thanks
  2. S

    What Is the Magnetic Force on a 1-cm Segment of a Current-Carrying Wire?

    A rectangular loop of wire measures 1.0 m by 1.0 cm. If a 7.0-A current flows through the wire, what is the magnitude of the magnetic force on the centermost 1.0-cm segment of the 1.0-m side of the loop? Fm = ILBsin of angle Fm = Magnetic force I= Electric current L= Length of...
  3. I

    Friction with induced coil and magnetic force

    Homework Statement As shown in the attached figure, two rails of conducting wire,M and N, run parallel to each other on a horizontal plane and are separated by distance l. The rails are in a magnetic field of magnetic flux density B that is in the vertically upward direction. An electrically...
  4. S

    Can a constant magnetic field cause circular motion?

    So, I have an apparent paradox: Consider a particle moving with constant velocity, v, along the x-axis. It now enters a constant magnetic field with is parallel to the y-axis. So there is a force, F=q(vxB) which acts on it, and points in the positive z-direction at first, but then as the...
  5. N

    Direction of the magnetic force

    Homework Statement The problem is in the attached image. Homework Equations The Attempt at a Solution I used the third left hand rule (seen in one of the attached images) and pointed my thumb (direction of the current) downwards because the question states that the current flows...
  6. G

    Relativistic explanation for magnetic force between perpendicular wires

    I have read about how magnetism arises from electric interactions and relativity. But in that respect i don't see how perpendicular wires can exert magnetic forces on each other. The movement of the charges is perpendicular so length contraction does not occurr in the direction of the current...
  7. J

    Central Magnetic Force between Earth and Moon

    Hey guys I have a question about central magnetic forces between the Earth-Moon system and how they would work at a very large scale similar to that of the central gravitational force. I don't know about electromagnetism as well as I do basic celestial mechanics, so I'm at a loss as to how I...
  8. U

    Is Principle of Relativity compatible with Magnetic force

    Hello friends, A while back I raised the similar question regarding absolute nature of Magnetic force due to a current carrying wire on a moving charge. But supposedly I was shown to be incorrect. Since, Magnetic filed is a relativistic effect, then every magnetic force should be...
  9. J

    What Is the Magnetic Force on a Single Electron?

    Homework Statement question - see image Homework Equations The Attempt at a Solution so I use the equation F = BIl F = 0.2 * 0.4 * 8 = 0.64 Surely I just divide it by the number of electrons (8*1028) to get the answer BUT this does not give the correct answer. The correct answer is D?
  10. B

    Magnetic force in a moving inertial reference frame

    A charged particle is placed next to a current-carrying wire. The wire produces a magnetic field, but if the particle is at rest, the field exerts no force on it. However, in a different inertial reference frame moving at speed v parallel to the wire, the particle is seen to be in motion, and so...
  11. D

    What Is The Relationship Between Temperature and Magnetic Force?

    Hi All, In an experiment I ran to determine the trend between distance and magnetic force (produced by an electromagnet) the result showed that the trend was either an inverse quartic or inverse quintic function. Such a result was unexpected as the trend is documented as being an inverse cubic...
  12. N

    Charges moving parallel to magnetic fields and direction of magnetic force

    I hope this isn't in the wrong forum, it's not a problem, just a conceptual question for physics 2. I have a few questions that I cannot find answer for in my physics book or online. 1) Why does moving a charge parallel to the magnetic field result in zero magnetic force? Is this quality...
  13. L

    Magnetic Force on Various Sides of Spinning Loop?

    Magnetic Force on Various Sides of Spinning Loop?? Homework Statement A horizontal uniform magnetic field of magnitude 0.4 T is oriented at an angle of = 65° relative to a line perpendicular to plane of a vertical, rectangular loop, as indicated in the figure. The loop has a height of 8 cm...
  14. T

    Physics Question about Magnetic Force & parallel wires

    I have a homework question that I am having some trouble with. This is my first post - so be easy on me. Question: A weight-lifter is able to hold a barbell with a maximum total mass of 205 kg above his head. A physicist uses him to conduct a classroom demonstration, asking him to hold one...
  15. T

    Magnetic force of one, moving charged particle on another (vector problem)

    Homework Statement At a particular instant, charge q_1 = 4.80×10^−6 C is at the point (0, 0.250m , 0) and has velocity v_1=(9.2*10^5 m/s) i_hat. Charge q_2 = −2.50×10^−6 C is at the point (0.150m , 0, 0) and has velocity v_2 = (-5.3x10^5 m/s) j_hat. At this instant, what is the magnetic...
  16. M

    In which situation is the magnetic force nonzero?

    Homework Statement A particle moves through a magnetic field. In which situation is the magnetic force nonzero? A. The charge is zero and the particle is moving perpendicular to the magnetic field. B. The charge is negative and the particle is moving in the direction of the magnetic field...
  17. D

    Magnetic Force Inverse Cubed Law?

    I was reading <crackpot link removed> and was wondering if the inverse cube law for magnetic force still applied for situations where the object being attracted isn't another magnet itself? E.g. if there is an electromagnet attracting an iron nut is the rule still inverse cube and not inverse...
  18. C

    Magnetic Force in a Current Carrying Wire

    Homework Statement The current in a wire consists of n electrons per unit volume moving with a velocity v. What is the effect on these electrons of the magnetic field set up by the current itself within the wire? What is the force on one electron at a distance r from the centre of the wire...
  19. A

    Magnetic Force Experienced by a Loop of Wire

    Homework Statement The problem is shown in the link below: http://postimage.org/image/do2b7xz0b/ Homework Equations Biot-Savart Law's and dF=Idl x B The Attempt at a Solution My attempt is really just a mess. I essentially want to break it up into 2 segments. (1) Being the...
  20. J

    Computing for magnetic force. Please check my answer.

    Homework Statement Find the magnitude and direction of the magnetic force on a charged particle with charge -4nC and velocity \vec{v} = (2.5\times 10^{4}) \hat{i} + (1.1 \times 10^{4}) \hat{j} (m/s) if the magnetic field in the region is given by \vec{B} = (1.2\times...
  21. E

    Amount of a magnetic force to alter the trajectory of a photon

    hello, I was just thinking since a photon trajectory is affected by a magnetic force.then I would like to know how much force does it take to do just so.
  22. N

    Magnetic Force Direction Question

    Homework Statement r= 0.12m B = 0.0720T I = 21.0A Fm= 0.104 N [up] A magnetic force of 0.104 N [up] acts on a 12.0cm long wire that runs[N 10 degrees E] through a magnetic field of 0.0720 T. If the current in the wire is 21.0 A, then what is the direction of the magnetic field? This...
  23. A

    Find magnetic force on semicircle using line integral

    Here is the question: A very thin wire which follows a semicircular curve C of radius R,lies in the upper half of the x-y plane with its center atthe origin. There is a constant current I flowing counter clockwise, starting upward from the end of the wire on the positive x-axis and ending...
  24. F

    Magnetic force does no work. OR does it?

    Hello Forum, it is well known that the magnetic force |F_mag|= q v B sin(theta) does no work on a moving charge particles, i.e. it does not increase or decrease its kinetic energy. It only changes its trajectory. However, in the examples of a U shaped wire loop with a movable metal bar...
  25. J

    Rod of current wire exerting magnetic force on current carrying bar

    Homework Statement Figure is attached. A thin copper bar of length = 14.0 cm is supported horizontally by two (nonmagnetic) contacts. The bar carries current I1 = 105 A in the -x direction, as shown in the figure below. At a distance h = 0.500 cm below one end of the bar, a long straight...
  26. G

    How Does a Magnetic Field Affect Liquid Levels in a U-Tube?

    Homework Statement A u-tube of uniform square cross section has electrodes sealed inside the upper and lower walls of the horizontal section. The two arms of tube being vertical. The tube is partially filled with liquid sodium and a direct current is passed between the electrodes. A uniform...
  27. P

    Magnitude of Magnetic force on Wire

    An isolated segment of wire of length L=4.50 m carries a current of magnitude i=35.0 A at an angle theta=50.3 degrees with respect to a constant magnetic field with magnitude B= 6.70E-2 T. What is the magnitude of the magnetic force on the wire? a) 2.66 N b) 3.86 c) 5.60 N d) 8.12 N e) 11.8...
  28. B

    Why does magnetic force tend to increase magnetic energy?

    Hello. So: Why does magnetic force tend to increase magnetic energy? 1) Usually, forces go in the direction of energy minimums. Why in this case is the opposite? 2) What does it imply? What is that makes magnetism particular in some senses, for example this, for example its force function...
  29. P

    Magnetic force on a current carrying wire

    Hi, I am slightly confused by the formula for finding the force on a current carrying wire. It is given as F=BIL where F is force, B is the strength of the magnetic field and L is the length of the wire being acted upon. What I don't understand is why this formula doesn't factor in the distance...
  30. F

    Is the magnetic force always 0?

    Homework Statement For any loop that may have symmetry, the magnetic force in the center must always be 0? Ex. circles, rectangles?
  31. T

    Questions about magnetic force between different strength magnets

    Hi, I have some very basic question that I've been struggling to find the answer to and before I go and buy some magnets to do some test of my own I thought I'd ask here: Do two magnets of different strength repulse each other at the same strength, or does one repulse the other more...
  32. R

    Magnetic force on a charged particle

    I am considering a positive charged particle moving with the velocity v into the magnetic field field B making an angle theta with the magnetic field, so the magnetic force exerted on the charged particle is perpendicular to the plane of B and v. My question is-Why the speed of the charged...
  33. S

    Would this wheel spin from magnetic force?

    Recently I was thinking random thoughts and thought to myself, if there was a windmill like wheel with powerful magnets on each blade, would it spin? Here is a poorly drawn picture to help explain myself: http://imageshack.us/photo/my-images/191/magneticwheel.png/ [WARNING -- a user has...
  34. E

    Calculating Peak Velocity of a Magnet Under Continuous Magnetic Force

    Homework Statement Imagine you have a magnet (Henceforth named MagX) which weighs .03lbs, and it is being continuously pushed by another magnet's polar likes (Henceforth named MagY) with a force of 3 PSI. Is it possible to find the peak velocity of MagX, assuming that MagY stays at a constant...
  35. I

    Magnetic force on rotating spherical shell

    Hi I was trying to do one problem from Griffiths's EM book. The problem says to find the magnetic force of attraction between the northern and southern hemispheres of a spinning charged spherical shell. There was an earlier problem in the book to find the electric force of attraction...
  36. S

    Magnetic force on ferromagnetic body

    Hello when we study electromagnetic ,it is easy to find force of a magnetic field on particle witch has electric charge (for example electron and ...) but what is force of magnetic field on ferromagnetic materials? for example if we put a cube of soft iron with a*a*a dimentions near a...
  37. M

    Magnetic Force Exerted on Particle

    Sorry for slightly disregarding the proper format but I'm really quite lost so I can abide by what is expected. However I will be detailed Question is: A particle with a mass of 6.64e-27 kg and a charge of +3.2e-19 C is accelerated from rest through a potential difference of 2.45e6 V. The...
  38. V

    Calculating Magnetic Force on a Steel Object in a Solenoid

    Hi There I want To calculate magnetic force in Solenoid. I need to relation between Force and (tesla, weight iron, and ...) F== B*M* ... is anybody here can help me ?
  39. B

    Show that the total magnetic force on the loop is zero

    Homework Statement a closed wire loop with current I is in a uniform magnetic field B show that the total magnetic force on the loop is zero Homework Equations The Attempt at a Solution everywhere that I've looked just states it without explaining why
  40. C

    Magnetic force of two parallel wires is inverse proportional to distance?

    according too: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/wirfor.html#c1F=(u * I *I2)/(2pi *r ) i thought it would be inverse proportional to the square of the distance?! can this be right?
  41. C

    Magnetic force between two parallel hanging wires

    Magnetic force between two parallel hanging wires (solved) Homework Statement Two long, parallel wires hang by 4.00-cm-long cords from a common axis. The wires have a mass per unit length of 1.30×10−2 kg/m and carry the same current in opposite directions. What is the current in each wire...
  42. W

    Magnetic force, coefficient of friction, forces in equilibrium

    A 1.0 kg copper rod rests on two horizontal rails 1.0 m apart and carries a current of 50 A from one rail to the other. The coefficient of static friction between rod and rails is 0.60. What are the (a) Magnitude and (b) Angle (relative to the vertical) of the smallest magnetic field that puts...
  43. T

    Magnetic Force on a Current Carrying Wire

    The figure shows a current i through a wire in a uniform magnetic field , as well as the magnetic force acting on the wire. The field is oriented so that the force is maximum. In what direction is the field? I have uploaded the figure, and the relevant equations. My reasoning: -L is in...
  44. D

    How does magnetic force cause a loop to contract

    Homework Statement 1. 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 above. The effect of the forces that act on this current is to make the loop (A) expand in size (B) contract in size...
  45. F

    Am I belitting this question? Magnetic force

    Homework Statement http://img710.imageshack.us/img710/9295/roachj.th.png Uploaded with ImageShack.us http://img146.imageshack.us/img146/6360/61565460.th.png Uploaded with ImageShack.usThe Attempt at a Solution The vertical conductors does nothing because their forces are only horizontal...
  46. J

    Right hand rule finding direction of magnetic force

    Homework Statement A strong magnet is placed under a horizontal conducting ring of radius r that carries current I as shown in the figure below. The magnetic field makes an angle θ with the vertical at the ring's location. (b) What is the direction of the resultant magnetic force on...
  47. F

    Calculating Magnetic Force on Ferrofluids Between Two Magnets

    I have the problem that I want to calculate the force of a magnet acting on a ferrofluid. I know this is is difficult but I am trying to make some simulations of physical behavior on ferrofluids Consider a U-shaped magnet with ferrofluid between the two poles. The distance between the poles...
  48. C

    Magnetic force for a current-carrying wire

    Homework Statement A high-voltage power lines carries a current of 110 A at a location where the Earth's magnetic field has a magnitude of .59 G and points to the north, 72 degrees below the horizontal. Find the direction and magnitude of the magnetic force exerted on a 250-m length of wire...
  49. A

    Finding magnetic field from magnetic force / semielliptical conductor

    Homework Statement 1) A charge Q is placed in a uniform magnetic field of magnitude a that proceeds in the -z direction. Its displacement is given by r(t) = (at^2+bt, 2bt, a). a) Find v(t). c) Find the magnetic force exerted on the charge at time t=t'. d) Now the magnetic field at time t'...
  50. jegues

    Magnetic Force due to current Parallel Wires

    Homework Statement See figure attached Homework Equations The Attempt at a Solution I've attempted to draw the magnetic fields resulting at the location of wire 4 due to wires 1, 2, 3. I denoted them as B4,1, as in the "The magnetic field at 4 as a result of 1". Are these...
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