Electromagnetic Field
Electromagnetic Field Overview
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The study of electromagnetism began in 1820 when Hans Christian Oersted discovered that electric currents produce magnetic fields (Oersted's law).
A magnetic field (sometimes called B-field is a physical field that describes the magnetic influence on moving electric charges, electric currents and magnetic materials.
Scale and Force of the Electromagnetic Force
Electromagnetic (EM) force fields can theoretically span to an infinite size, as the electromagnetic force has an infinite range, weakening only as the inverse square of the distance from the source.
Electromagnetic force fields operate at both the classical level (Newton and Einstein) and the quantum level (atomic and subatomic).
(In practice, however, the size and strength of a manageable or effective field are limited by the energy required to create them and the physical constraints of the apparatus generating them. The universe is enormous and the space between particles vast.)
Key Aspects of Size and Strength Limits:
- Fundamental Range: The electromagnetic force, is carried by photons, and operates across the entire universe, meaning a field's influence never truly hits a zero limit, although it becomes negligible at great distances.A photon is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. A photon is a Gauge Boson. Photons, W and Z bosons, and gluons are gauge bosons.
- Natural Magnets (Largest):
Magnetars: The largest known coherent magnetic fields exist around magnetars (a type of neutron star), which can generate fields roughly 10 to the 15th Gauss or 10 to the 11th Tesla )
- This means a value of 1,000,000,000,000,000 Gauss, or one quadrillion Gauss. This immense field strength is typically found only in extreme astrophysical objects such as magnetars. By way of comparison, a strong refrigerator magnet has a field of about 10,000 μT (100 G).
Earth's magnetic field also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic field is generated by electric currents due to the motion of convection currents of a mixture of molten iron and nickel in Earth's outer core: these convection currents are caused by heat escaping from the core, a natural process called a geodynamo.
It is the earth's electromagnetic field that provides the directional force in an everyday compass.
- Man-Made Limits (Small to Moderate Size):
On Earth, the strongest sustained, human-made magnetic fields are in the range of tens to 100 Tesla. These are generally confined to small, specialized laboratory spaces (a few centimeters or less) because stronger fields create forces that destroy the magnets themselves.
- "Force Field" Shielding (Plasma):
For shielding applications, plasma-based systems (like those being tested for ion thrusters) are often confined within vacuum chambers. While plasma can be directed, creating a large, self-sustaining "plasma bubble" (a sci-fi style force field) is constrained by the massive power required to ionize and confine the air or particles.
- Practical Constraints: The limiting factor for size is energy density. A field large enough to cover a vehicle or ship would require power sources vastly exceeding current, conventional technology, and would likely require superconducting materials that can withstand intense internal magnetic pressures.
In summary, while the influence of a field can be infinite, a concentrated, high-intensity, and actionable EM force field is practically restricted to small-scale, high-energy, and typically metallic, superconducting, or plasma-confined environments.
Magnetic fields are expressed most strongly in certain metallic materials—specifically ferromagnetic materials like iron, nickel, and cobalt due to their unique atomic structure, which allows unpaired electron spins to align in the same direction, creating large magnetic domains. In most other materials, electron spins are either paired (canceling each other out) or oriented randomly, resulting in no net magnetic behavior.
Here is a detailed breakdown of why this phenomenon is restricted to specific metals:
1. Unpaired Electrons and Alignment (Quantum Mechanics)
- The Source of Magnetism: Magnetism at the atomic level arises from electrons spinning around the nucleus and on their own axes. In most materials, electrons are paired in opposite directions, canceling their magnetic moments.
- The Ferromagnetic Exception: In ferromagnetic metals (iron, cobalt, nickel, and some alloys), the crystal structure ensures that numerous electrons in the 3d shell are unpaired.
- Exchange Interaction: Due to quantum mechanical effects called "exchange interaction," the spins of these unpaired electrons in neighboring atoms align, creating strong magnetic "domains". In most other materials (like wood, plastic, or copper), these interactions are not strong enough to align the electrons.
2. Magnetic Domains
- Unmagnetized Metal: In their natural state, these magnetic domains in iron or nickel are oriented in random directions, resulting in zero net magnetic force.
- Magnetized State: When an external magnetic field is applied, these domains rotate and align in the same direction, creating a powerful, additive magnetic field.
3. High Magnetic Permeability
- Metals, particularly iron, have high magnetic permeability, meaning they allow magnetic field lines to pass through them very easily.
- A magnetic field will "choose" to travel through a metal object rather than through air or plastic, resulting in a strong attraction as the magnetic field seeks the lowest energy path.
4. Comparison with Other Materials
- Non-Magnetic Materials: In materials like plastic, glass, or aluminum, the electrons do not have the specific configuration required to form long-range, aligned domains, making them almost entirely non-responsive to magnetic fields.
- Diamagnetic/Paramagnetic Materials: While all materials have some magnetic response (diamagnetism), it is typically millions of times weaker than the ferromagnetic response found in metals.
Summary of Metallic Types
Not all metals are strongly magnetic. They are classified based on their response to a field:
- Ferromagnetic (Strongly Magnetic): Iron, Cobalt, Nickel, and their alloys (steel).
- Paramagnetic (Weakly Attracted): Aluminum, Platinum.
- Diamagnetic (Weakly Repelled): Copper, Gold, Silver.
A number of figures collectively carried Maxwell's classical field theory through its relativistic reformulation and into the quantum era in which Dirac finally placed the electron and the electromagnetic field on a relativistic quantum footing.
It is important to note that aspects of electromagnetic forces are still a focus of research and discovery particularly in the quantum realm. For example the field of spintronics.
The Electromagnetic Spectrum Overview
You Tubes on Electromagnetism
Electromagnetism - Vocabulary (lexicon)
Electromagnetic Greats that advanced our Electromagnetic Knowledge
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Alessandro Volta inventor of the battery
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Wiki: Hans Christian Ørsted, Danish physicist - discovered that electric currents create magnetic fields.(Oersted's law)
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Wiki: Michael Faraday, English physicist - discoveries include the principles underlying electromagnetic induction, diamagnetism, and electrolysis.
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Charles-Augustin de Coulomb, French physicist - discoverer of what is now called Coulomb's law, the description of the electrostatic force of attraction and repulsion
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André-Marie Ampère, French Physicist - an important founder of the science of classical electromagnetism,
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Carl Friedrich Gauss, German mathematician, astronomer, geodesist, and physicist measured the Earth's magnetic field strength in 1832 and created the first electromagnetic telegraph
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Wiki: James Clerk Maxwell, Scottish physicist and mathematician - responsible for the classical theory of electromagnetic radiation, which was the first theory to describe electricity, magnetism and light as different manifestations of the same phenomenon.
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wiki: Heinrich Hertz, German physicist conclusively proved the existence of the electromagnetic waves proposed by James Clerk Maxwell's equations of electromagnetism.
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Wiki: Paul Dirac British Physicist - laid the foundations for both quantum electrodynamics and quantum field theory
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Electromagnetic Spectrum News and Developments
Metrology - If you can't measure it you can't understand it. If you can't understand it you can't harness it.
The Science of Measurement
Simple Electromagnetic Experiments for beginner scientsts
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