phy4

Fundamentals of Magnetism

I. Definition of Terms

a. Magnet
  • Definition: A magnet is defined as a material capable of interacting with other materials, easily influenced by magnetism.
  • Etymology: The term 'magnet' originates from the ancient Greek place Magnesia, where most of the known lodestones were found in ancient times.
b. Magnetic Pole
  • Definition: The magnetic pole of a magnet is the region that exhibits polar characteristics, meaning it has both a north and a south pole.
c. Magnetic Field
  • Definition: A magnetic field is the field of force that surrounds a magnet.
  • Creation: It is created from a changing electric field, which stems from the movement of electric charges.
  • Direction: The orientation and direction of the magnetic field are determined by the right-hand rule, which provides a way to visualize the direction of the magnetic field relative to the current direction.
d. Lorentz Force
  • Definition: The Lorentz force is the total force acting on a charged particle in an electromagnetic field, influenced by both electric and magnetic forces.
  • Formula: The Lorentz force is represented by the equation:
    extbfFL=qextbfE+qextbfvimesextbfBextbf{F}_L = q extbf{E} + q extbf{v} imes extbf{B}
  • Special Case (Magnetic Force): Eliminating the electric field component leads to the expression for the magnetic force:
    extbfFB=qextbfvimesextbfBextbf{F}_B = q extbf{v} imes extbf{B}
i. Electric and Magnetic Forces
  • Electric Force:

    • Projection: The electric force acts in a direction parallel to the electric field.
    • Effect on Charges: It causes a moving charge to change its direction in accordance with the electric field's projection.
  • Magnetic Force:

    • Projection: The magnetic force operates perpendicular to the directions of both the electric field and the magnetic field.
    • Effect: It changes the trajectory of a moving charge in a manner perpendicular to the magnetic field direction.
e. Cyclotron Radius
  • Definition: The cyclotron radius represents the radius of the circular motion of a charged particle in a magnetic field.
  • Formula:
    r<em>g=mv</em>qBr<em>g = \frac{mv</em>{\bot}}{qB}
f. Cyclotron Frequency
  • Definition: The cyclotron frequency defines the angular frequency of a charged particle's circular motion in a magnetic field.
  • Behavioral States:
    • When the Lorentz force equals the magnetic force:
    1. If qvB > rac{mv^2}{r}, the charged particle moves in a spiral path, trapped within the magnetic field.
    2. If qvB < rac{mv^2}{r}, the movement is an arc as the particle escapes the field.
    3. If qvB=mv2rqvB = \frac{mv^2}{r}, the movement is circular.
  • Formula:
    extAngularFrequency:extwg=qBmext{Angular Frequency: } ext{w}_g = \frac{qB}{m}
g. Magnetic Flux
  • Definition: Magnetic flux quantifies the strength of a magnetic field passing through a specific area.
  • Unit: The unit for magnetic flux is the Weber.
  • Conversion:
    • 1extWb=1extVexts1 ext{ Wb} = 1 ext{ V} ext{s}
  • Formula:
    extΦB=BAextcos(heta)ext{Φ}_B = BA ext{cos}( heta)
  • Implication: In a closed surface, the total magnetic flux is equal to zero:
    extTotalMagneticFlux=0ext{Total Magnetic Flux} = 0
h. Solenoid
  • Definition: A solenoid is a conducting wire coiled in a helical shape, functioning similarly to multiple single-loop conductors arranged in parallel.
i. Biot-Savart Law
  • Definition: This law describes how a magnetic field is generated by changing electric fields and is consistent with both Ampere’s and Gauss’s Laws.
  • Formula:
    extdextbfB=extμ0I4extπextdextbflextsin(heta)r2ext{d} extbf{B} = \frac{ ext{μ}_0 I}{4 ext{π}} \frac{ ext{d} extbf{l} ext{sin}( heta)}{r^2}
j. Ampere's Law
  • Definition: Ampere's Law relates the current flowing through a conductor to the magnetic field it generates.
  • Formula:
    B=extμ0IextencB = \frac{ ext{μ}_0 I}{ ext{enc}}

II. FORMULAE Variations

a. Biot-Savart Law Current Distribution
  1. Point in the Magnetic Field
    • Long Straight Conductor:
      B=extμ0I2extπrB = \frac{ ext{μ}_0 I}{2 ext{π} r}
    • Long Cylindrical Conductor:
      • Inside the conductor:
        B=extμ0I2extπrR2B = \frac{ ext{μ}_0 I}{2 ext{π} r R^2}
      • Outside the conductor:
        B=extμ0I2extπrB = \frac{ ext{μ}_0 I}{2 ext{π} r}
    • Long Solenoid (nearly ideal), with number of loops per length:
      • Inside the solenoid:
        B=extμ0nIB = ext{μ}_0 n I
      • Outside the solenoid:
        B=0B = 0
    • Moving Charge:
      • At distance:
        B=extμ04extπqvr2B = \frac{ ext{μ}_0}{4 ext{π}} \frac{q v}{r^2}
    • Circular loop with a specific radius:
      • Loop as an arc with central angle φφ (in radians):
        B=extμ0I2extπrR2B = \frac{ ext{μ}_0 I}{2 ext{π} r R^2}
      • Center of complete loop at origin:
        B=extμ0I2rB = \frac{ ext{μ}_0 I}{2r}
      • Distance given (a) above or below origin:
        B=extμ0I4extπrB = \frac{ ext{μ}_0 I}{4 ext{π} r}
b. Ampere's Law Shape of the Conductor Formula
  1. Ring / Toroid:
    B=extμ0NI2extπrB = \frac{ ext{μ}_0 N I}{2 ext{π} r}
  2. Loop:
    B=extμ0NI2rB = \frac{ ext{μ}_0 N I}{2r}
  3. Solenoid:
    B=extμ0nIB = ext{μ}_0 n I
  4. Straight Wire:
    B=extμ0I2extπrB = \frac{ ext{μ}_0 I}{2 ext{π} r}

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