## Definitions for Electricity and Magnetism

When two objects in each other's vicinity have different electrical charges, an electricfield exists between them. An electric field also forms around any single object that is electrically charged with respect to its environment. An object is negatively charged (—) if it has an excess of electrons relative to its surroundings. An object is positively charged (+) if it is deficient in electrons with respect to its surroundings.

An electric field has an effect on other charged objects in the vicinity. The field strength at a particular distance from an object is directly proportional to the electric charge of that object, in coulombs.The field strength is inversely proportional to the distance from a charged object.

Flux is the rate (per unit of time) in which something flowing crosses a surface perpendicular to the direction of flow.

An alternative expression for the intensity of an electric field is electric flux density. This refers to the number of lines of electric flux passing at right angles through a given surface area, usually one meter squared (1 m2). Electric flux density, like electric field strength, is directly proportional to the charge on the object. But flux density diminishes with distance according to the inverse-square law because it is specified in terms of a surface area (per meter squared) rather than a linear displacement (per meter).

INTERNATIONAL SYSTEM PREFIXES

 SI prefix Symbol Multiplying factor exa- E 1018 = 1,000,000,000,000,000,000 peta- P 1015 = 1,000,000,000,000,000 tera- T 1012 = 1,000,000,000,000 giga- G 109 = 1,000,000,000 mega- M 106 = 1,000,000 kilo- K 103 = 1,000 hecto- h 102 = 100 deca- da 10 = 10 deci- d 10-1 = 0.1 centi- c 10-2 = 0.01 milli- m 10-3 = 0.001 micro- ^ or u 10-6 = 0.000,001 nano- n 10-9 = 0.000,000,001 pico- p 10-12 = 0.000,000,000,001 femto- f 10-15 = 0.000,000,000,000,001 atto- a 10-18 = 0.000,000,000,000,000,001

A note on nonmetric prefixes: In the United States, the word billion means the number 1,000,000,000, or 109. In most countries of Europe and Latin America, this number is called "one milliard" or "one thousand million," and "billion" means the number 1,000,000,000,000, or 10'2, which is what Americans call a "trillion." In this set, a billion is 109.

A note on nonmetric prefixes: In the United States, the word billion means the number 1,000,000,000, or 109. In most countries of Europe and Latin America, this number is called "one milliard" or "one thousand million," and "billion" means the number 1,000,000,000,000, or 10'2, which is what Americans call a "trillion." In this set, a billion is 109.

NAMES FOR LARGE NUMBERS

 Number American European SI prefix 109 billion milliard giga- 1012 trillion billion tera- 1 0 15 quadrillion billiard peta- 1018 quintillion trillion exa- 1021 sextillion trilliard zetta- 1024 septillion quadrillion yotta- 1027 octillion quadrilliard 1030 nonillion quintillion 1033 decillion quintilliard 1036 undecillion sextillion 1039 duodecillion sextilliard 1042 tredecillion septillion 1045 quattuordecillion septilliard

This naming system is designed to expand indefinitely by factors of powers of three. Then, there is also the googol, the number 10'00 (one followed by '00 zeroes). The googol was invented for fun by the eight-year-old nephew of the American mathematician Edward Kasner. The googolplex is '0googo[ or one followed by a googol of zeroes. Both it and the googol are numbers larger than the total number of atoms in the universe, thought to be about '080.

This naming system is designed to expand indefinitely by factors of powers of three. Then, there is also the googol, the number 10'00 (one followed by '00 zeroes). The googol was invented for fun by the eight-year-old nephew of the American mathematician Edward Kasner. The googolplex is '0googo[ or one followed by a googol of zeroes. Both it and the googol are numbers larger than the total number of atoms in the universe, thought to be about '080.

A magneticfield is generated when electric charge carriers such as electrons move through space or within an electrical conductor. The geometric shapes of the magnetic flux lines produced by moving charge carriers (electric current) are similar to the shapes of the flux lines in an electrostatic field. But there are differences in the ways electrostatic and magnetic fields interact with the environment.

Electrostaticflux is impeded or blocked by metallic objects. Magnetic flux passes through most metals with little or no effect, with certain exceptions, notably iron and nickel.These two metals, and alloys and mixtures containing them, are known as ferromagnetic materials because they concentrate magnetic lines of flux.

Magnetic flux density and magnetic force are related to magnetic field strength. In general, the magnetic field strength diminishes with increasing distance from the axis of a magnetic dipole in which the flux field is stable. The function defining the rate at which this field-strength decrease occurs depends on the geometry of the magnetic lines of flux (the shape of the flux field).