Physics equations/Magnetic forces

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Magnetic forces: Lorentz and Laplace][edit | edit source] The Lorentz force is the combination of electric and magnetic force on a point charge due to electromagnetic fields. If a particle of charge q moves with velocity v in the presence of an electric field E and a magnetic field B, then it will experience a force

(in SI units). 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 particle which might be traveling near the speed of light (relativistic form of the Lorentz force).

If the charged particles are travelling in a wire we have the Laplace force:

  • Problem: A wire segment that is 2.5 meters long carries a current of 12 amps in a 3.5 Tesla field. What is the force on the segment if the angle between the wire and the magnetic field is 30 degrees? *
(click for answer)

Since sin 30° = ½, we have

next ptoble[edit | edit source]

If , then


Here only the first (and far simpler) problem is solved. Both variants of the right-hand rule stipulate that each element of length in the line integral contributes an element of magnetic field that points in the same direction, as shown in the figures below:

References[edit | edit source]