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UNITS OF ELECTRICAL MEASUREMENT
Ohms Law - h1011v1_39

Electrical Science Volume 1 of 4
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UNITS OF ELECTRICAL MEASUREMENT Basic Electrical Theory Current Electron  current,  or  amperage,  is  described  as  the  movement  of  free  electrons  through  a conductor.  In electrical formulas, current is symbolized with a capital I, while in the laboratory or on schematic diagrams, it is common to use a capital A to indicate amps or amperage (amps). Resistance Now that we have discussed the concepts of voltage and current, we are ready to discuss a third key  concept  called  resistance.    Resistance  is  defined  as  the  opposition  to  current  flow.   The amount  of  opposition  to  current  flow  produced  by  a  material  depends  upon  the  amount  of available  free  electrons  it  contains  and  the  types  of  obstacles  the  electrons  encounter  as  they attempt to move through the material.  Resistance is measured in ohms and is represented by the symbol  (R)  in  equations.   One  ohm  is  defined  as  that  amount  of  resistance  that  will  limit  the current  in  a  conductor  to  one  ampere  when  the  potential  difference  (voltage)  applied  to  the conductor is one volt.  The shorthand notation for ohm is the Greek letter capital omega (W).  If a voltage is applied to a conductor, current flows.  The amount of current flow depends upon the resistance  of  the  conductor.   The  lower  the  resistance,  the  higher  the  current  flow  for  a  given amount of voltage.   The higher the resistance, the lower the current flow. Ohm’s Law In 1827, George Simon Ohm discovered that there was a definite relationship between voltage, current, and resistance in an electrical circuit.   Ohm’s Law defines this relationship and can be stated in three ways. 1. Applied  voltage  equals  circuit  current  times  the  circuit  resistance.   Equation  (1-2)  is  a mathematical respresentation of this concept. E = I x R    or    E = IR (1-2) 2. Current is equal to the applied voltage divided by the circuit resistance.   Equation (1-3) is a mathematical representation of this concept. (1-3) I E R ES-01 Page 14 Rev. 0







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