Magnetism

Magnetism

1. History and Impact

   • 600 BC (Lodestones)
     • Greeks discovered that they attract themselves and metallic objects
   • XIII BC (Compass)
     • Chinese made the compass
   • Oersted (Danish)
     • Electric current conductor wire diverted a compass needle (1820)
       • André Ampère made some similar experiments
   • Michael Faraday and Joseph Henry
     • Electromagnetic induction
       • A magnet moving near to a conducting coil produces a spiral current

2. Magnetic Interaction

   • Greeks discovered magnetite that atrracted pieces of not magnetized iron
     • Magnetism
       • Force of attraction that is experimented
     • Magnet
       • Object that exerts the magnetic force
         • Electron motion in a organized way
       • Poles
         • Regions with more concentration of force
         • Law of Magnetic Force
           • Repel
             • Equal magnetic poles
           • Attract
             • Different magnetic poles
         • If a magnet is cuted in half
           • Magnet always have north and south pole
             • No matter its size
               • Weaker in small pieces
             • Poles cannot be isolated
       • Magnetic Field
         • Vector Field
           • Magnitude
           • Direction
             • From north to south pole
               • Inward from its south pole
               • Points outward from its north
         • A charge generates an electric field around it and also a magnetic field if the electric field it is moving
           • If a charge is moving inside an external magnetic field, the field produced by the moving charge will interact and exert a force
             • Magnetic force on a moving charge
               • Magnetic field B and moving charge q interact
                 • q has a velocity v
               • Vector
                 • Direction
                   • Given by the right hand rule
                     • Right Hand
                       • Positive Charges
                     • Left Hand
                       • Negative Charges
                     • Pointing with four fingers in the direction of the magnetic field with the hand extended, curling them in the direction of the particles motion (direction velocity)
                       • Thumb indicate the direction of the force
                 • Magnitude
               • Magnetic Force
                 • Whe acts over a postive charge q moving at velocity v, is perpendicular to v and magnetic fiel B
                   • For given values of velocity and intensity of a magnetic field, the force is greater when they are perpendicular.
                 • The resulting force in conductors produces a moment of torsion with radius (r)
                   • Useful for the calculation of electric motors
                 • By the interaction between two bodies are produced by the interaction between moving electrons in the atoms that make up the bodies
                   • Electromagnetic Theory
               • Force in a current carrying conductor
                 • If the charge charge is distributed along a conductor
                   • Wire or conductor with a length L
                     • That moves with a velocity v
                       • Rearranging terms
                         • q/t can be replaced with current (I)
                           • Force over the conductor is:
                   • Vector
                     • Direction
                       • RHR
                     • Magnitude
         • Space in which magnetic effects are present
           • Magnetic Field Lines
             • Visualize magnetic fields
               • Just as electric field lines describes electric fields

3. Magnetic Field Sources and Oersted´s Experiment

   • Permanent
     • Magnetite
   • Non-Permanent
     • Electromagnet
   • Danish scientist found that the Electric Current produces a Magnetic Field
     • Produce torque over the compass
     • First connection between Electricty and Magnetism

4. Biot-Savart Experiments (Biot and Savart - Physicists)

   • Calculate the Magnetic Field (B) produced by any any type of current flowing on a wire
     • By performing the experiments of Magnetic Fields near to different kinds of circuits
     • Superposition Principle for Magnetic Fields
       • “The total magnetic field produced by several moving charges is the vector sum of the fields produced by individual charges”
         • Integral is the addition of the contributions to the total magnetic field done by very small segments of the wire were the current is flowing
       • Geometry
         • Long Current-Carrying conductor
         • Circular Coil (Center), magnetic induction is perpendicular to the plane of the coil
           • N Number of Windings (Center)
         • Circular Coil with N Number of Windings (Any Distance in the Center Axis)
         • Inside a Solenoid
           • Coiled wire with many helical turns
           • Or Toroid Doughnut-Shaped
     • Hall Effect Sensor
       • Experiment used to measure Magnetic Fields
         • Prove Biot-Savart Formula

5. Electricity and Magnetism

   • Electric Charge at Rest = Electric Field
   • Electric Charge is Moving = Electric and Magnetic Field

6. Examples

   • Our planet as a giant magnet
   • Aurera Borealis
   • Electronic Devices
     • Loudspeaker
     • Printer
     • Electric motor
     • Television
     • Hard Disk
     • Magnetically levitated trains
   • MIR
     • Magnetic Resonance Imaging
       • Strong magnetic fields and radio frequency (RF) waves
         • Form images of body
         • Diseases detected
           • Tumors
           • Brain Infection
           • Multiple Sclerosis

7. Ampere’s Law

   • High Simmetry
     • Relation between Magnetic Field and Electric Current
       • RHR (Positive Direction)
     • Easier than Biot-Savart Law
   • Current Stable
     • No Magnetic Materials or Electric Fields around

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