Thousands of genera Phanerozoic biodiversity as shown by the fossil record Mass extinctions are thought to result when a long-term stress is compounded by a short term shock. In general, large extinctions may result when a biosphere under long-term stress undergoes a short-term shock. High diversity leads to a persistent increase in extinction rate; low diversity to a persistent increase in origination rate. These presumably ecologically controlled relationships likely amplify smaller perturbations asteroid impacts, etc.
If a similar ball is charged by the same glass rod, it is found to repel the first: Two balls that are charged with a rubbed amber rod also repel each other. However, if one ball is charged by the glass rod, and the other by an amber rod, the two balls are found to attract each other.
These phenomena were investigated in the late eighteenth century by Charles-Augustin de Coulombwho deduced that charge manifests itself in two opposing forms. This discovery led to the well-known axiom: The magnitude of the electromagnetic force, whether attractive or repulsive, is given by Coulomb's lawwhich relates the force to the product of the charges and has an inverse-square relation to the distance between them.
Electric charge gives rise to and interacts with the electromagnetic forceone of the four fundamental forces of nature. The most familiar carriers of electrical charge are the electron and proton. Experiment has shown charge to be a conserved quantitythat is, the net charge within an electrically isolated system will always remain constant regardless of any changes taking place within that system.
The charge on electrons and protons is opposite in sign, hence an amount of charge may be expressed as being either negative or positive.
By convention, the charge carried by electrons is deemed negative, and that by protons positive, a custom that originated with the work of Benjamin Franklin. Charge is possessed not just by matterbut also by antimattereach antiparticle bearing an equal and opposite charge to its corresponding particle.
Electric current The movement of electric charge is known as an electric currentthe intensity of which is usually measured in amperes. Current can consist of any moving charged particles; most commonly these are electrons, but any charge in motion constitutes a current. Electric current can flow through some things, electrical conductorsbut will not flow through an electrical insulator.
Current defined in this manner is called conventional current. The motion of negatively charged electrons around an electric circuitone of the most familiar forms of current, is thus deemed positive in the opposite direction to that of the electrons.
The positive-to-negative convention is widely used to simplify this situation. An electric arc provides an energetic demonstration of electric current The process by which electric current passes through a material is termed electrical conductionand its nature varies with that of the charged particles and the material through which they are travelling.
Examples of electric currents include metallic conduction, where electrons flow through a conductor such as metal, and electrolysiswhere ions charged atoms flow through liquids, or through plasmas such as electrical sparks.
While the particles themselves can move quite slowly, sometimes with an average drift velocity only fractions of a millimetre per second, : That water could be decomposed by the current from a voltaic pile was discovered by Nicholson and Carlisle ina process now known as electrolysis.
Their work was greatly expanded upon by Michael Faraday in Current through a resistance causes localised heating, an effect James Prescott Joule studied mathematically in The level of electromagnetic emissions generated by electric arcing is high enough to produce electromagnetic interferencewhich can be detrimental to the workings of adjacent equipment.
These terms refer to how the current varies in time. Direct current, as produced by example from a battery and required by most electronic devices, is a unidirectional flow from the positive part of a circuit to the negative.
Alternating current is any current that reverses direction repeatedly; almost always this takes the form of a sine wave. The time-averaged value of an alternating current is zero, but it delivers energy in first one direction, and then the reverse.
Alternating current is affected by electrical properties that are not observed under steady state direct current, such as inductance and capacitance. Electric field See also: Electrostatics The concept of the electric field was introduced by Michael Faraday.
An electric field is created by a charged body in the space that surrounds it, and results in a force exerted on any other charges placed within the field. The electric field acts between two charges in a similar manner to the way that the gravitational field acts between two massesand like it, extends towards infinity and shows an inverse square relationship with distance.
Gravity always acts in attraction, drawing two masses together, while the electric field can result in either attraction or repulsion. Since large bodies such as planets generally carry no net charge, the electric field at a distance is usually zero.
Thus gravity is the dominant force at distance in the universe, despite being much weaker. As the electric field is defined in terms of forceand force is a vectorso it follows that an electric field is also a vector, having both magnitude and direction.
Specifically, it is a vector field. The field may be visualised by a set of imaginary lines whose direction at any point is the same as that of the field.
This concept was introduced by Faraday,  whose term ' lines of force ' still sometimes sees use. The field lines are the paths that a point positive charge would seek to make as it was forced to move within the field; they are however an imaginary concept with no physical existence, and the field permeates all the intervening space between the lines.
The field is therefore zero at all places inside the body. The principles of electrostatics are important when designing items of high-voltage equipment.
There is a finite limit to the electric field strength that may be withstood by any medium.MJ Bioscience Spin-off As a result of the Plan of Arrangement, Highmark Marketing will transfer to MJ Bioscience all of the intellectual property related to its cannabis research and development.
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