Lec 7: Forces and Fields to EM Theory Flashcards Preview

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Flashcards in Lec 7: Forces and Fields to EM Theory Deck (9)
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1
Q

Faraday 1930 - Kinds of electricity?

A

1832, Faraday tries to relate different kind of electricities

  • > searched for unity between electrostatic generators, voltaic cells, thermocouples, dynamos, electric fixshes
  • > those like John Davy’s (Humphry’s bro) thought E effects were complex combinations of many powers

Studies conduction in liquids

  • > I flows through all water solutions
  • > up to this point, can’t measure quantities of electricity
  • > not sure if different electricity -> same effects

Designs an apparatus to measure electricity

  • > products of electrolysis proportional to their chemical combining weights
  • > second law of electrolysis

With William Whewell, introduces terms

  • > electrolysis
  • > electrolyte
  • > electrode
  • > anode
  • > cation
  • > cathode

Ion = electrified substances transported through liquids in electrolysis

Realised there was a proportion of elements set free to a standard current

  • > Helmholtz shows this is charge of electron
  • > but Faraday don’t like atomic theory, or electrical atoms
2
Q

Faraday’s Electricity Measuring Device

A
  • > glass tube, with two electrodes in it
  • > both electrodes go to a test tube filled with water
  • > connecting the terminals to electricity passes current through water
    • > water –> H + O, as gas in top of each tube
    • > can see amount of gas produced
      • > which in proportion to electricity passed through it
  • > later version, each electrode gets own tube
    • > H and O in individual tubes
3
Q

Electricity as a Force?

A

Faraday observed static electricity discharging through air via blotting paper (soaked with an electrolyte)

  • > challenges standard electrical theories of action at a distance
  • > no poles?
  • > electricity is A FORCE, not a MATERIAL
  • > “current” is rupture/re-establishment of bonds as ions migrate through solution

This explains insulators and currents through wires

  • > insulator = can sustain high Electric force without the molecular chain breaking
  • > good conductor = weak, can sustain very little intermolecular strain - the strain builds and breaks rapidly

Thought this explained all phenomena of electricity

  • > and E as a force and interactions with materials can explain Magnetism
  • > if E is a force, B is a force (and not a liquid!)
  • > but why does B only act on certain materials (iron, nickel, cobalt), unlike E?
4
Q

Magnetic Fields and Light?

A

Faraday tried using a powerful electromagnet rather than static

  • > B can affect a ray of light!
  • > pass a polarized ray of light through a highly refractive substance along a magnetic line of force
    • > will rotate plane of polarization, proportional to |B|

Led him to Universality of Magnetism

  • > tried to show all bodies affected by a B
  • > leads to DIA/PARAMAGNETISM
  • > also tries to link gravity/B, fails
5
Q

Diamagnetics and Paramagnetics?

A

Dia: Conduct B poorly
->in a uniform B, lines of force diverge

Para: Conducts B well

  • > in uniform B, lines of force converge on the body
  • > the lines of force cluster on entry and exit from the body
    • > these are the POLES of induced magnets
6
Q

JCM (1831-1879)

A

Sees Faraday’s description of E & M good for mathematical description

  • > formulates it all into mathematical equations
  • > known as ELECTROMAGNETIC THEORY

Such a based man, Faraday’s influence is primarily through him. However, JCM modified F’s theory:

  • > JCM said matter and the field are different entities
  • > Newton says each body exerts spooky force, the field is just book keeping to express it
  • > JCM says the bodies interact indirectly via their fields
    • > but he still separated matter & force
      • > electric force consists of forces per unit charge, NOT fields of force
7
Q

Electromagnetic Theory

A

Magnetism and Electricity cannot exist separately!

  • > shows E field created by oscillation of I
  • > radiates outward from source at 186k miles/s
  • > problem with C - so light is an electric charge too!
8
Q

Heinrich Rudolf Hertz (1857-1894)

A

Created a circuit that would produce long-wave radiation, if light was a kind of EM radiation

  • > metal rod with gap at midpoint
  • > sparks cross gap, causing violent high f oscillations
  • > proved they are transmitted through air, by detecting them some distance away

Showed this radiation was like light

  • > they could reflect, refract, polarize
  • > SAME SPEED but longer wavelength
    • > 1M times the size
  • > “Hertzian waves”, confirm Maxwell’s prediction of EM waves
    • > leads to radio communication, TV, radar
9
Q

Guglielmo Marconi (1874-1937)

A
  • > saw application of Hertz’s waves to Morse code
  • > used to form Marconi’s Wireless Telegraph Co
  • > first wireless internation transmission, En-Fr
  • > 1901, cross Atlantic