Module 3: Très Basses Fréquences Électromagnétiques

Module 3: Les Très Basses Fréquences du Spectre Électromagnétique - Notions de Base

• Magnétostatique: Study of magnetic phenomena where the magnetic field doesn't change over time.
• Aimant: A material capable of attracting certain metallic objects. Some materials are naturally magnetic (ferromagnetic), others are only affected by a magnetic field (paramagnetic).
• Pôles: Magnets have two inseparable poles: North and South. Like poles repel, opposite poles attract.
• Champ magnétique: A magnet creates a magnetic field (B).
• Champ électrique et champ magnétique: A continuous electric current can induce a magnetic field. A current (I) passing through a wire creates a magnetic field (B). The direction of the magnetic field is determined by the right-hand rule.
• Unités: The SI unit for magnetic field strength is the Tesla (T). The Gauss (G) is also used, with 1 Gauss = 10^-4 Tesla.
• Lignes de champ: Magnetic field lines are curves; the magnetic field vector is tangent to the field line at each point. The closer the lines, the stronger the magnetic field.

Loi de Biot-Savart

• Définition: Defines the magnetic field created by a moving charged particle (at velocity v) at a fixed point (M). The formula is:
  B(M) = μ₀q v x r / 4πr³
• Notation: μ₀ is the permeability of free space. v x r is the cross product of the velocity vector and the vector pointing from the charge (q) to the point M. r is the distance between the charge and the point.
• Vectorial nature: The magnetic field is a vector quantity. The cross product of two vectors produces another vector (w = u x v). The direction of the produced vector is perpendicular to both u and v.

Formules à Connaître (Page 3)

• Fil rectiligne infini: Formula for magnetic field strength produced by an infinitely long, straight wire.
• Spire circulaire: Formula for magnetic field strength produced by a circular loop of wire.
• Solénoïde: Formula for magnetic field strength inside a solenoid (a coil of wire).
• Bobine toroïdale: Formula for magnetic field strength inside a toroidal coil (a doughnut-shaped coil of wire).
• Force de Lorentz: Formula for the force acting on a charged particle moving in a magnetic field.
• Force de Laplace (Force sur un conducteur): Formula for the force acting on a current-carrying wire in a magnetic field.
• Rayon de Larmor: Formula relating the radius of a particle's circular orbit in a uniform magnetic field to its mass, charge, and velocity.

Ondes Électromagnétiques (Pages 4-5)

• Nature ondulatoire et corpusculaire: Electromagnetic waves are transverse waves made of oscillating electric and magnetic fields. They can also be viewed as streams of photons.
• Nature ondulatoire: Waves spread out from a source that has a disturbance that propagates from one place to another. Energy transfers, but matter doesn't.
• Dualité onde/particules: Light and other electromagnetic radiation exhibit wave and particle properties. This duality is fundamental in quantum mechanics.
• Spectre électromagnétique: Various types of electromagnetic radiation, such as radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays, arranged in order of increasing frequency and decreasing wavelength.
• Spectre de raies et spectre continu: Types of spectra that indicate the energy levels of matter. A line spectrum occurs when only certain frequencies of photons are emitted or absorbed. A continuous spectrum, on the other hand, has an infinite range of frequencies.
• Polarisation: Light waves can be polarized, meaning the electric field oscillations are restricted to a particular direction. This can affect the interaction between light and matter.

RMN (Résonance Magnétique Nucléaire) (Pages 7-8)

• Définition: NMR is a physical phenomenon that occurs in certain atomic nuclei that possess spin (a type of angular momentum).
• Applications: MRI (medical imaging).
• Spin nucléaire: Some atomic nuclei have a property called nuclear spin, a form of angular momentum that generates a magnetic moment.
• Moment magnétique: The magnetic moment associated with the nucleus provides a measure of the nucleus's tendency to line up with an external applied magnetic field
• Effet d'un champ magnétique extérieur: When a nucleus is in a magnetic field, its spin can take on two energies orientations (aligned with or opposed to the field).
• Fréquence de Larmor: The frequency at which a nuclear magnetic dipole precesses in a magnetic field; a characteristic frequency for a particular nucleus.
• Perturbation: A radiofrequency pulse (a changing magnetic field) is used to excite or flip the spins of nuclei.
• Relaxation: After the perturbation, the nuclei return to their equilibrium state, emitting energy in the form of a detectable signal.

Spectre électromagnétique (Page 6)

• Gamme d'énergie: The electromagnetic spectrum covers a wide range of energies, from very low to very high.
• Ionisation: Radiation with energy above a threshold (typically 13.6 eV for hydrogen) can remove electrons from atoms, leading to ionization.

Ce quiz couvre les notions de base sur la magnétostatique, les aimants, et les champs magnétiques. Vous apprendrez l'interaction entre le champ électrique et le champ magnétique ainsi que les unités de mesure. Testez vos connaissances sur ces concepts clés de l'électromagnétisme.