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Unification of Electricity and Magnetism

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Title: Unification of Electricity and Magnetism


1
Unification of Electricity and Magnetism
  • Maxwells theory combining Faradays law and
    Amperes law

2
Unifications
  • There have been several important Unifications in
    Physics
  • Unification of Electricities
  • Unification of Electricity and Magnetism
  • Special Relativity
  • Unification of EM and Quantum Mechanics
  • Unification of EM and Weak Force
  • Yet to come
  • Unification of Gravity and Quantum Mechanics

3
What is so Special about Unification?
  • Is it nothing more than being able to write down
    a theory in one equation instead of two?
  • Each Unification brought with it a surprise, a
    new understanding, and new phenomenon
  • Putting the pieces of a puzzle together revealed
    missing pieces

4
Unification of Electricity and Magnetism
  • James Clerk Maxwell combined
  • Faradays law describing how electric field is
    made from magnetic field
  • Amperes law describing how magnetic field is
    made from current
  • Gauss law describing how electric field is made
    from charge
  • into a single set of equations

5
Michael Faraday September 1821
6
Electric Field
  • The force between charge is given by Coulombs
    law

7
Electric Field
8
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9
Electric and Magnetic Fields
10
Electric Fields from Magnets
  • When a current flows through a wire a magnetic
    field circles the wire
  • If currents can make magnetic fields, can magnets
    make electric fields?
  • When a magnet is moving through a coil a voltage
    is induced at the ends of the coil
  • This is known as Faraday Induction and is the key
    principle for the operation of all motors and
    generators

11
Magneto-Electricity
  • The magnetic field moving through the coil can be
    either
  • A magnet that inserted into the coil
  • A magnetic field produced by a current in, for
    example, another coil
  • Faraday Induction

12
Early Generator
  • Two sets of coils
  • One with a current to make a magnetic field
  • The second had a voltage induced
  • Device was based on steam engine technology

13
James Clerk Maxwell
  • Born 1831
  • Color Vision, 1850
  • Saturns Rings, 1855
  • Statistical and Molecular Physics, 1859
  • A dynamical Theory of the Electric Field, 1864

14
Amperes Law
The magnetic field around a loop is proportional
to the current going through the loop
Magnetic Field inside a Solenoid
15
Maxwells Addition
Maxwell added another term to Amperes Law one
that had not been observed
16
Faraday Induction
  • Maxwell did not have the advantage of vector
    notation. In describing the magnetic field he
    used three functions, F, G, H, for the components
    of the field.

17
Speed of Light
  • After 85 pages of derivations, Maxwell was able
    to find the equation for an electro-magnetic
    wave.
  • The velocity of the wave was close to the speed
    of light

18
Unification of Electricity and Magnetism
  • The connection Faradays Law connected Electric
    Field to Magnetic Field
  • The Unified Theory Maxwell, by adding
    displacement current, came up with the single
    theory describing electricity and magnetism
  • The surprise - Light is an electromagnetic wave
  • Further examination of the theory lead to the
    predictions of Special Relativity

19
Conclusion
  • This is the first of the theoretical unifications
  • Unifications are foreshadowed by a connection
    in this case the electric and magnetic field
  • We will see similar connections next time when we
    look at
  • unification of EM with Quantum Mechanics
  • unification of Special Relativity with Quantum
    Mechanics
  • unification of the Electric and Weak forces
  • unification of Gravity and Quantum Mechanics
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