Charges/Interactions/Electromagnetics

Diffraction spikes ("sunstars") at f/8, note the eight points. Credit: Lewis Collard.

Electromagnetics is most familiar as light, or electromagnetic radiation.

"Laser pulses have been made to accelerate themselves around loops of optical fibre - which seems to go against Newton’s 3rd law. This states that for every action there is an equal and opposite reaction."

On the right are diffraction spikes ("sunstars") at f/8. Note the eight points. This is caused by the 18-70 mm DX having 8 aperture blades.

Charges

Main resource: Charges

File:Chargon and spinon separation.png

The locus of the abrupt change in conductance that clearly moves away from the 1D parabola is the chargon. Credit: Y. Jompol, C. J. B. Ford, J. P. Griffiths, I. Farrer, G. A. C. Jones, D. Anderson, D. A. Ritchie, T. W. Silk and A. J. Schofield.

Charge is usually thought of as a property of matter that is responsible for electrical phenomena, existing in a positive or negative form.

Charge interactions

Main resources: Charges/Interactions and Charge interactions

"Under Newton’s third law of motion, if we imagine one billiard ball striking another upon a pool table, the two balls will bounce away from each other. If one of the billiard balls had a negative mass, then the collision of the two balls would result in them accelerating in the same direction."

The relative strengths and ranges of the charge interactions:

Interaction	Mediator	Relative Magnitude	Behavior	Range
Strong interaction	gluon	1038	1	10−15 m
Electromagnetic interaction	photon	1036	1/r2	universal
Weak interaction	W and Z bosons	1025	1/r5 to 1/r7	10−16 m
Gravity interaction	photon?	10	1/r2	universal

From an electromagnetic-type interaction point of view, the gravity interaction, or gravitational interaction, is a heavily charge-balanced ever so slight excess of positive charge amounting to 10^-36 of a proton for the mass of a proton. Gravity owes its ability to attract other objects due to their apparent charge excess often represented by mass.

Quanta

Main resources: Charges/Quanta and Quanta

"Quantum mechanics however states that matter cannot have a negative mass. Negative mass is not the same as antimatter, as even antimatter has positive mass. Negative mass is a hypothetical concept of matter where mass is of opposite sign to the mass of normal matter. Negative mass is used in speculative theories, such as the construction of wormholes. Should such matter exist, it would violate one or more energy conditions and show strange properties. No material object has ever been found that can be shown by experiment to have a negative mass."

Effective masses

Main resources: Charges/Effective masses, Effective masses, Masses, and Mass

File:Light loops diagram.jpg

The light going around the longer loop is relatively delayed. Credit: New Scientist.

"When a material such as layered crystals slows the speed of the light pulse in proportion to its energy, it is behaving as if it has mass. This is called effective mass, which is the mass that a particle appears to have when responding to forces. Light pulses can have a negative effective mass depending on the shape of their light waves and the structure of the crystal material that the light waves are passing through."

"The pulses were split between the loops at a contact point and the light kept moving around each [loop] in the same direction. The key to the experiment was having one loop slightly longer than the other. This meant light going around the longer loop is relatively delayed, as shown by the diagram [on the right]."

"When the light completes a circuit and splits at the contact point, some of its photons are shared with pulses within the other loop. After a few circuits, the pulses develop an interference pattern that gives them effective mass."

Pulses "with both positive and negative effective mass [were created]. When the opposing pulses interacted in the loops, they accelerated in the same direction and moved past the detectors a little bit earlier after each trip. The loops are essentially the equivalent of having extremely long crystals."

Electromagnetic radiation

Main resources: Radiation/Electromagnetics, Electromagnetic radiation, and Electromagnetics

The electromagnetic interaction is a fundamental force of nature that is felt by charged [particles]. Its exchange particle is the photon (symbol γ) and the many forms of electromagnetic radiation are a manifestation of this interaction.

Electromagnetic fields

Sources of electromagnetic fields consist of two types of charge – positive and negative.

Rutherford scattering

Rutherford scattering showed that the electromagnetic field has a greater range than the weak or strong fields and charged particles usually interact electromagnetically before other fields have a chance to operate.

Continual exchange

Electromagnetic interactions are long range attractions or repulsions between any particles or antiparticles that have charge. If the particles are attracted they stay together, because there is a continual exchange of photons.

Above the nuclear scale

The electromagnetic force is the one responsible for practically all the phenomena one encounters in daily life above the nuclear scale. Roughly speaking, all the forces involved in interactions between atoms can be explained by the electromagnetic force acting on the electrically charged atomic nuclei and electrons inside and around the atoms, together with how these particles carry momentum by their movement. This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which come from the intermolecular forces between the individual molecules in our bodies and those in the objects. It also includes all forms of chemical phenomena.

Electrons move between interacting atoms.

Electric fields

Main resources: Charges/Interactions/Electromagnetics/Electric fields and Electric fields

The electric field E is defined such that, on a stationary charge:

$\mathbf {F} =q_{0}\mathbf {E}$

where q₀ is what is known as a test charge. The size of the charge doesn't really matter, as long as it is small enough not to influence the electric field by its mere presence. What is plain from this definition, though, is that the unit of E is N/C (newtons per coulomb). This unit is equal to V/m (volts per meter).

In electrostatics, where charges are not moving, around a distribution of point charges, the forces determined from Coulomb's law may be summed. The result after dividing by q₀ is:

$\mathbf {E(r)} ={\frac {1}{4\pi \varepsilon _{0}}}\sum _{i=1}^{n}{\frac {q_{i}\left(\mathbf {r} -\mathbf {r} _{i}\right)}{\left|\mathbf {r} -\mathbf {r} _{i}\right|^{3}}}$

where n is the number of charges, q_i is the amount of charge associated with the ith charge, r_i is the position of the ith charge, r is the position where the electric field is being determined, and ε₀ is the electric constant.

Magnetic fields

Main resources: Charges/Interactions/Electromagnetics/Magnetic fields and Magnetic fields

In a material,

$\mathbf {B} =\mu _{0}(\mathbf {H} +\mathbf {M} ).$

The quantity $\mu _{0}\mathbf {M}$ is called magnetic polarization.

Lorentz forces

The electromagnetic field exerts the following force (often called the Lorentz force) on charged particles:

$\mathbf {F} =q\mathbf {E} +q\mathbf {v} \times \mathbf {B}$

where all boldfaced quantities are vectors: F is the force that a charge q experiences, E is the electric field at the location of the charge, v is the velocity of the charge, B is the magnetic field at the location of the charge.

The above equation illustrates that the Lorentz force is the sum of two vectors. One is the cross product of the velocity and magnetic field vectors. Based on the properties of the cross product, this produces a vector that is perpendicular to both the velocity and magnetic field vectors. The other vector is in the same direction as the electric field. The sum of these two vectors is the Lorentz force.

Electrons

Main resources: Charges/Electrons and Electrons

Light in fibers can have effective mass just as "electrons in semiconductors can also have effective mass".

Accelerations

Main resources: Physics/Accelerations and Accelerations

"In the most striking of the new experiments a pulse of light that enters a transparent chamber filled with specially prepared cesium gas is pushed to speeds of 300 times the normal speed of light. That is so fast that, under these peculiar circumstances, the main part of the pulse exits the far side of the chamber even before it enters at the near side."

"Our light pulses can indeed be made to travel faster than c. This is a special property of light itself, which is different from a familiar object like a brick."

"In the usual arrangement, one beam of light is shone on the chamber, exciting the cesium atoms, and then a second beam passing thorugh the chamber soaks up some of that energy and gets amplified when it passes through them."

"But the amplification occurs only if the second beam is tuned to a certain precise wavelength."

"By cleverly choosing a slightly different wavelength, Dr. Wang induced the cesium to speed up a light pulse without distorting it in any way."

"If you look at the total pulse that comes out, it doesn't actually get amplified."

"There is a further twist in the experiment, since only a particularly strange type of wave can propagate through the cesium. Waves Light signals, consisting of packets of waves, actually have two important speeds: the speed of the individual peaks and troughs of the light waves themselves, and the speed of the pulse or packet into which they are bunched. A pulse may contain billions or trillions of tiny peaks and troughs. In air the two speeds are the same, but in the excited cesium they are not only different, but the pulses and the waves of which they are composed can travel in opposite directions".

"These so-called backward modes are not new in themselves, having been routinely measured in other media like plasmas, or ionized gases. But in the cesium experiment, the outcome is particularly strange because backward light waves can, in effect, borrow energy from the excited cesium atoms before giving it back a short time later. The overall result is an outgoing wave exactly the same in shape and intensity as the incoming wave; the outgoing wave just leaves early, before the peak of the incoming wave even arrives."

The "cesium chamber reconstructs the entire pulse solely from information contained in the shape and size of the tail, and spits the pulse out early."

"If the side of the chamber facing the incoming wave is called the near side, and the other the far side, the sequence of events is something like the following. The incoming wave, its tail extending ahead of it, approaches the chamber. Before the incoming wave's peak gets to the near side of the chamber, a complete pulse is emitted from the far side, along with a backward wave inside the chamber that moves from the far to the near side."

"The backward wave, traveling at 300 times c, arrives at the near side of the chamber just in time to meet the incoming wave. The peaks of one wave overlap the troughs of the other, so they cancel each other out and nothing remains. What has really happened is that the incoming wave has "paid back" the cesium atoms that lent energy on the other side of the chamber."

"A paper on the second new experiment, by Daniela Mugnai, Anedio Ranfagni and Rocco Ruggeri of the Italian National Research Council, described what appeared to be slightly faster-than-c propagation of microwaves through ordinary air, and was published in the May 22 issue of Physical Review Letters. [They] used an ingenious set of reflecting optics to create microwave pulses that seemed to travel as much as 25% faster than c over short distances."

Recent history

Main resources: History/Recent and Recent history

The recent history period dates from around 1,000 b2k to present.

Originally electricity and magnetism were thought of as two separate forces.

In 1873, the interactions of positive and negative charges were shown to be regulated by one force. There are four main effects resulting from these interactions, all of which have been clearly demonstrated by experiments:

1. Electric charges attract or repel one another with a force inversely proportional to the square of the distance between them: unlike charges attract, like ones repel.
2. Magnetic poles (or states of polarization at individual points) attract or repel one another in a similar way and always come in pairs: every north pole is yoked to a south pole.
3. An electric current in a wire creates a circular magnetic field around the wire, its direction (clockwise or counter-clockwise) depending on that of the current.
4. A current is induced in a loop of wire when it is moved towards or away from a magnetic field, or a magnet is moved towards or away from it, the direction of current depending on that of the movement.

Hypotheses

Main resource: Hypotheses

1. Each of the three interactions: the strong interaction, electromagnetic interaction, and the weak interaction are all derivable from an expression of variable exponent.
2. Electromagnetics such as light or electromagnetic radiation are a special manifestation of a more general electromagnetic-type interaction.

See also

• Charge interactions
• Circuit astronomy
• Coronal cloud
• Dynamos
• Electromagnetic interaction
• Electrostatics
• Electroweak interaction
• Empty spaces
• Magnetic reconnections
• Magnetohydrodynamics
• Magnetostatics
• Natural electric fields
• Radiative dynamos
• Weak interactions
• Weak forces
• Stellar surface fusion
• Strong interactions

Further reading

• Edward Mills Purcell (1985). Electricity and Magnetism Berkeley Physics Course Volume 2 (2nd ed.). McGraw-Hill. ISBN 0-07-004908-4. 
• Moliton, André (December 2006). Basic electromagnetism and materials. New York City: Springer-Verlag New York, LLC. pp. 430. ISBN 978-0-387-30284-3. http://books.google.com/?id=2kPAIlxjDJwC&printsec=copyright&q=fundamental. 

External links

{{Physics resources}}{{Radiation astronomy resources}}