Introduction of Electromagnetic Induction

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Introduction of Electromagnetic Induction

• BY
• Zhaoxin Peng
• Shui He
• Xiao Yang

Instructor John Hopkins
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Prevailing View before the Discovery of
Electromagnetic Induction

• Ancient electrical, magnetic, and optical effects
  have been known since antiquity. the ability of
  some materials, notably amber, when rubbed to
  attract bits of cloth or paper and the lodestone
  or natural magnet.

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Prevailing View before the Discovery of
Electromagnetic Induction

• Hans Christian Oersted (1777-1851), was
  philosophically convinced of the unification of
  the forces in nature. He therefore set out to
  show that electricity and magnetism were related.
  It had long been known that lightning would cause
  compasses to deflect. As soon as Oersted heard of
  Volta's discovery he tried to get a galvanic
  current to deflect a magnet. In 1820 he published
  his results. They were immediately recognized as
  important and widely demonstrated. The unit of
  magnetic intensity is now called an oerstead.

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Prevailing View before the Discovery of
Electromagnetic Induction

• Andre Marie Ampere (1775-1836), heard Oersted's
  results presented at the French Academie de
  Sciences on 11 Sept, 1820 by Arago. Within one
  week Ampere developed a complete quantitative
  theory of Oersted's observation and succeeded in
  laying the foundation of a mathematical theory of
  electromagnetism. He refined and perfected his
  theory in the following years and published it in
  1827. This treatise had at its foundation four
  experiments. In effect, he showed that two
  parallel conductors carrying electricity in the
  same direction attract each other, whereas if the
  currents are in opposite directions, the
  conductors repel one another. From the
  experiments he claimed
• Outside its body, a permanent magnet is exactly
  equivalent in its magnetic action to a coil of
  wire carrying a current. (He called the coil a
  solenoid.)
• Each molecule in permanent magnet has a closed
  current loop.
• Magnetization is the alignment of the molecules
  with an external magnetic field (he didn't call
  it a field").
• The unit of electrical current is now called the
  ampere.

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Discovery of Electromagnetic Induction

• In 1820, a Danish physicist, Hans Christian
  Oersted, discovered that a magnetized needle is
  deflected, when placed next to a wire through
  which current is passing. This simple
  observation, led to speculation that a reverse
  effect also existed, i.e. that a current can be
  caused to flow in a conductor exposed to a
  magnetic field.
• Eleven years later, in 1831, the English chemist
  and physicist, Michael Faraday, demonstrated that
  this was indeed true. Faraday also demonstrated
  that plane polarized light was rotated in a
  strong magnetic field, the significance of this
  is that it demonstrated the connection between
  light and magnetism. The following diagram
  illustrates the principle of electromagnetic
  induction.

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Discovery of Electromagnetic Induction
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Basic Concepts

• Magnetic Field
• A magnetic field is a field that permeates space
  and which exerts a magnetic force on moving
  electric charges and magnetic dipoles. Magnetic
  fields surround electric currents, magnetic
  dipoles, and changing electric fields.
• B magnetic flux density
• Unit Tesla(TWb/m2 kgs-2A-1 NA-1m-1)
• Fm Magnetic flux
• Unit Weber(WbVs/Akgm2s-2A-2)

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Basic Concepts

• Ampere's Law Magnetic Force on a Current

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Basic Concepts

• Faraday's Law
• Any change in the magnetic environment of a coil
  of wire will cause a voltage (emf) to be
  "induced" in the coil. No matter how the change
  is produced, the voltage will be generated. The
  change could be produced by changing the magnetic
  field strength, moving a magnet toward or away
  from the coil, moving the coil into or out of the
  magnetic field, rotating the coil relative to the
  magnet, etc.

E Electromotive Force (EMF) N the number of
coils t time Fm Magnetic flux B Magnetic flux
density S Area the magnetic flux pass through
vertically

E-N(? Fm/ ?t) -N(?SB/ ?t)
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Basic Concepts
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Basic Concepts

• Lenz's Law
• When an emf is generated by a change in magnetic
  flux according to Faraday's Law, the polarity of
  the induced emf is such that it produces a
  current whose magnetic field opposes the change
  which produces it. The induced magnetic field
  inside any loop of wire always acts to keep the
  magnetic flux in the loop constant. In the
  examples below, if the B field is increasing, the
  induced field acts in opposition to it. If it is
  decreasing, the induced field acts in the
  direction of the applied field to try to keep it
  constant.

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The application of Faradays Law

• AC Generator
• The turning of a coil in a magnetic field
  produces motional emfs in both sides of the coil
  which add. Since the component of the velocity
  perpendicular to the magnetic field changes
  sinusoidally with the rotation, the generated
  voltage is sinusoidal or AC. This process can be
  described in terms of Faraday's law when you see
  that the rotation of the coil continually changes
  the magnetic flux through the coil and therefore
  generates a voltage.

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The application of Faradays Law

• Generator and Motor
• A hand-cranked generator can be used to generate
  voltage to turn a motor. This is an example of
  energy conversion from mechanical to electrical
  energy and then back to mechanical energy.

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Impact to our society

• The discovery of Faradays Law establish the
  fundamental requirement for the second industrial
  revolution. The invention of AC generator caused
  the alteration of the energy structure from
  mechanical to electrical power. Hence, the
  efficiency of world industries turned into a
  brand new era.

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Impact to our society

• With the application of AC generator, the power
  plant was invented later. Thus the applications
  of electric light, tramcar, telegraph, electrical
  engines and so on, soon became possible.

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Impact to our society

• Since the energy structure was altered from
  mechanical to electrical power based, the
  pressure on the environment from industries was
  mitigated. The polluted emissions were replaced
  by millions miles of electricity transmitter.

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Citation

• http//hyperphysics.phy-astr.gsu.edu/hbase/magneti
  c/forwir.htmlc1
• http//en.wikipedia.org/wiki/Electromagnetism
• http//www.vuse.vanderbilt.edu/rap2/papers/em_his
  tory.pdf