Micro (μ) means one-millionth (1⁄1,000,000). Milli (m) means one-thousandth (1⁄1,000). Kilo (k) means one thousand (1,000).  Mega (M) means one million (1,000,000).  Kilo is one of the most extensively used conversion factors. It  explains the use of prefixes with basic units of measurement.  Kilo means 1,000, and when used with volts, is expressed as  kilovolt, meaning 1,000 volts. The symbol for kilo is the letter  “k.” Thus, 1,000 volts is one kilovolt or 1 kV. Conversely,  one volt would equal one-thousandth of a kV, or 1 ⁄1,000 kV. This could also be written 0.001 kV.  Similarly, the word “milli” means one-thousandth, and  thus, 1 millivolt equals one-thousandth (1⁄1000) of a volt.  Figure 12-5  contains a complete list of the multiples used to  express electrical quantities, together with the prefixes and  symbols used to represent each number.  Electricity is often described as being either static or dynamic.  The difference between the two is based simply on whether  the electrons are at rest (static) or in motion (dynamic). Static  electricity is a buildup of an electrical charge on the surface  of an object. It is considered “static” due to the fact that there  is no current flowing as in alternate current (AC) or direct  current (DC) electricity. Static electricity is usually caused  when non-conductive materials, such as rubber, plastic, or  glass, are rubbed together causing a transfer of electrons,  which results in an imbalance of charges between the two  materials. The fact that there is an imbalance of charges  between the two materials means that the objects will exhibit  an attractive or repulsive force.  Although most objects become charged with static electricity  by means of friction, a charged substance can also influence  objects near it by contact.  [Figure 12-7]  If a positively-charged  rod touches an uncharged metal bar, it draws electrons from  the uncharged bar to the point of contact. Some electrons enter  the rod, leaving the metal bar with a deficiency of electrons  (positively charged) and making the rod less positive than it  was or, perhaps, even neutralizing its charge completely.  A method of charging a metal bar by induction is  demonstrated in  Figure 12-8 . A positively-charged rod is  brought near, but does not touch, an uncharged metal bar.  Electrons in the metal bar are attracted to the end of the bar  nearest the positively-charged rod, leaving a deficiency of  electrons at the opposite end of the bar. If this positively- charged end is touched by a neutral object, electrons will  flow into the metal bar and neutralize the charge. The metal  bar is left with an overall excess of electrons.  A field of force exists around a charged body. This field is  an electrostatic field (sometimes called a dielectric field) and  is represented by lines extending in all directions from the  charged body and terminating where there is an equal and  opposite charge.  To explain the action of an electrostatic field, lines are used  to represent the direction and intensity of the electric field  of force. As illustrated in  Figure 12-9 , the intensity of the  field is indicated by the number of lines per unit area, and  the direction is shown by arrowheads on the lines pointing  in the direction in which a small test charge would move (or  tend to move) if acted upon by the field of force. 12-5  Figure 12-5.  Prefixes and symbols for multiples of basic quantities.  Number  Prefix  Symbol  1,000,000,000,000  tera  t  1,000,000,000  giga  g  1,000,000  mega  M  1,000  kilo  k  100  hecto  h  10  deka  dk  0.1  deci  d  0.01  centi  c  0.001  milli  m  0.000001  micro  µ  0.000000001  nano  n  0.000000000001  pico  p  Electrostatic Field  Static Electricity  Attractive and Repulsive Forces  One of the most fundamental laws of static electricity, as  well as magnetics, deals with attraction and repulsion. Like  charges repel each other and unlike charges attract each other.  All electrons possess a negative charge and as such repel each  other. Similarly, all protons possess a positive charge and  as such repel each other. Electrons (negative) and protons  (positive) are opposite in their charge and attract each other.  For example, if two pith balls are suspended, as shown in  Figure 12-6 , and each ball is touched with the charged glass  rod, some of the charge from the rod is transferred to the balls.  The balls now have similar charges and, consequently, repel  each other as shown in part B of  Figure 12-6 . If a plastic rod  is rubbed with fur, it becomes negatively charged and the  fur is positively charged. By touching each ball with these  differently charged sources, the balls obtain opposite charges  and attract each other as shown in part C of  Figure 12-6 . 