Electro-Magnetism

  • Magnetism : A force caused by moving electric charges. It can attract or repel materials like iron, cobalt, and nickel.
  • Magnetic Field : A region around a magnetic material or current-carrying wire where magnetic forces can be observed.
  • Magnetic Field Lines : Imaginary lines that show the direction of the magnetic field.
    • They flow from north to south outside the magnet.
  • Magnetic Dipole : A magnetic system with two poles – north and south – like a bar magnet or a current loop.
  • Gauss’s Law for Magnetism: The net magnetic flux through any closed surface is zero.
    • This implies magnetic monopoles don’t exist.
  • Coulomb’s Law in Magnetism: No direct Coulomb’s law like in electrostatics. However, magnetic poles interact in a similar inverse-square law fashion.
  • Oersted’s Experiment: Demonstrated that electric current produces a magnetic field.
  • Right-Hand Thumb Rule: Used to find the direction of the magnetic field around a current-carrying wire.
  • Fleming’s Left-Hand Thumb Rule: Used to find the direction of force on a current-carrying conductor in a magnetic field.
  • Lorentz Law : Describes the force on a charged particle due to electric and magnetic fields.
  • Magnetic Induction (B): Magnetic field induced in a material when placed in an external magnetic field.
  • Magnetic Permeability(μ): Measure of how easily a material can support the formation of a magnetic field.
  • Intensity of Magnetization (I or M): Magnetic moment per unit volume of a material.
  • Magnetic Force or Magnetic Intensity (H): The external magnetic field applied to a material.
  • Magnetic Flux (Φ): Total magnetic field passing through a surface;
    • Φ = B·A·cosθ.
  • Magnetic Susceptibility (χ): The ratio of intensity of magnetization (M) to magnetic field intensity (H);
    • χ = M / H.
    • Paramagnetic : Materials weakly attracted to magnetic fields (χ > 0).
    • Diamagnetic : Materials repelled by magnetic fields (χ < 0).
    • Ferromagnetic : Materials strongly attracted and can retain magnetization (e.g., iron).
    • Curie Temperature : The temperature above which ferromagnetic materials become paramagnetic.
  • Hysteresis Loss : Energy loss in magnetic materials due to the lag between magnetization and the external field.
  • Inductor : A coil of wire that stores energy in a magnetic field when current flows through it.
  • Inductance : (L): Property of an inductor to resist change in current;
    • L = (NΦ)/I.
  • Choke Coil : An inductor used to block high-frequency AC while allowing DC to pass.
  • Magnetic Force (on a moving charge): 𝐹 ⃗ = 𝑞 ( 𝑣 ⃗ × 𝐵 ⃗ ) 
  • Solenoid : A long coil of wire that produces a uniform magnetic field when current passes.
  • Toroid : A donut-shaped coil used to produce a confined magnetic field.
  • Transformer :
    • Device using mutual induction to change voltage levels in AC circuits.
  • Self Induction : The process in which a changing current in a coil induces an EMF in the same coil.
  • Mutual Inductance : When a change in current in one coil induces an EMF in a nearby coil.
  • Electro Magnetic Induction : Generation of EMF by changing magnetic flux.
  • Faraday Laws of EMI : 
    • An EMF is induced when magnetic flux through a circuit changes.
    • The magnitude of induced EMF is proportional to the rate of change of flux.
  • Lenz’s Law : The direction of induced EMF opposes the change in flux that caused it.
  • Eddy Current : Loops of induced current in conductors exposed to changing magnetic fields; cause energy loss as heat.
Electro-Magnetism