The dreadnought was the predominant type of battleship in the early 20th-century. The first of the kind, the Royal Navy’s Dreadnought, had such an impact when launched in 1906 that similar battleships built after her were referred to as “dreadnoughts”, and earlier battleships became known...
Health and safety
The potential health effects of the very low frequency EMFs surrounding power lines and electrical devices are the subject of on-going research and a significant amount of public debate. In workplace environments, where EMF exposures can be up to 10,000 times greater than the average,...
Time-varying EM fields in Maxwell’s equations
Main articles: near and far field, electromagnetic radiation, virtual particle, dielectric heating, and magnetic induction An EM field that varies in time has two “causes” in Maxwell’s equations. One is charges and currents (so-called “sources”), and the other cause for an E or B field...
Static E and B fields and static EM fields
Main articles: electrostatics, magnetostatics, and magnetism When an EM field (see electromagnetic tensor) is not varying in time, it may be seen as a purely electrical field or a purely magnetic field, or a mixture of both. However the general case of a static EM...
Electromagnetic field as a feedback loop
The behavior of the electromagnetic field can be resolved into four different parts of a loop: the electric and magnetic fields are generated by electric charges, the electric and magnetic fields interact with each other, the electric and magnetic fields produce forces on electric charges,...
Dynamics of the electromagnetic field
In the past, electrically charged objects were thought to produce two different, unrelated types of field associated with their charge property. An electric field is produced when the charge is stationary with respect to an observer measuring the properties of the charge, and a magnetic...
Discrete structure
The electromagnetic field may be thought of in a more ‘coarse’ way. Experiments reveal that in some circumstances electromagnetic energy transfer is better described as being carried in the form of packets called quanta (in this case, photons) with a fixed frequency. Planck’s relation links...
Continuous structure
Classically, electric and magnetic fields are thought of as being produced by smooth motions of charged objects. For example, oscillating charges produce electric and magnetic fields that may be viewed in a ‘smooth’, continuous, wavelike fashion. In this case, energy is viewed as being transferred...
Photoelectric effect
Main article: Photoelectric effect In another paper published in that same year, Albert Einstein undermined the very foundations of classical electromagnetism. His theory of the photoelectric effect (for which he won the Nobel prize for physics) posited that light could exist in discrete particle-like quantities,...
Classical electrodynamics
Main article: Classical electrodynamics The scientist William Gilbert proposed, in his De Magnete (1600), that electricity and magnetism, while both capable of causing attraction and repulsion of objects, were distinct effects. Mariners had noticed that lightning strikes had the ability to disturb a compass needle,...
