THE magnetic force, or Lorentz force, it is the result of the interaction between two bodies endowed with magnetic properties, such as magnets or electrical charges in motion.
In the case of electrical charges, the magnetic force comes into being when an electrically charged particle moves in a region where a magnetic field acts.
Whereas a one-off charge Q, with speed v, is released in a region where there is a uniform magnetic fieldB, a magnetic force acts on it with an intensity given by the following equation:
F = Q.v. B.senα
*α is the angle between the velocity vectors v and the magnetic field B.
THE magnetic field direction is perpendicular to the plane containing the vectors. v and F, and the meaning is given by the right hand rule. Look at the picture:
The right hand rule shows the direction of velocity, field and magnetic force.
See that the middle finger points in the direction of the magnetic field B, the indicator indicates the speed direction V with which the load moves and the thumb points in the direction of the magnetic force F.
The movement acquired by the electric charge when it comes into contact with the magnetic field depends on the angle at which it was launched:
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When the launched particle has a velocity parallel to the lines of induction of the magnetic field, the magnetic force is nil.
Note that in this case the angle α = 0° or α = 180°. The equation we use to calculate force is:
F = Q.v. B.senα.
And sin 0º = sin 180º = 0
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Substituting it in the equation, we will have:
F = Q.v. B.0
F = 0
If the force is equal to zero, the particle maintains the same velocity and performs uniform rectilinear movement in the same direction as the magnetic field.
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Particle launched perpendicular to the magnetic field: the angle between v and B will be α = 90º. As sin 90º = 1, we will have:
F = Q.v. B.sen 90
F = Q.v. B.1
F = Q.v. B
The movement performed by the particle is circular and uniform, and the radius of its trajectory is obtained as follows:
F = Fcp
We know that:
F = Q.v. B and Fcp = mv2
RWe match the expressions and get:
Q.v. B = mv2
RR = mv
Q.BThe greater the particle's mass, the greater the radius of its trajectory.
Particle launched obliquely to field lines: In this case, we must consider the x and y components of the velocity vector. The speed vx has the same direction as magnetic field lines, while vy is perpendicular. The resultant of the velocity causes a circular and uniform movement, with a direction perpendicular to vector B, which can be called uniform helical.
The unit of measurement of the magnetic force is the same as for any other type of force: the Newton. There are numerous applications of magnetic force, among them, we can mention the speed selectors, electric motors and galvanometers.
By Mariane Mendes
Graduated in Physics
Would you like to reference this text in a school or academic work? Look:
TEIXEIRA, Mariane Mendes. "Magnetic Force"; Brazil School. Available in: https://brasilescola.uol.com.br/fisica/forca-magnetica.htm. Accessed on June 27, 2021.
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