current

                                                                    current

   Electricity is the flow of free electrons in a conductor from one atom to the next atom in the same general direction

. This flow of electrons is referred to as current and is

designated by the symbol “I”.  Electrons move through a conductor at different rates and electric current has different values

Current

that pass through

a cross-section of a conductor

is determined by the number of electrons 

in one second

current is measured in amperes which is abbreviated

“amps”. The letter “A” is the symbol for amps.

                  Units of Measurement

Prefix                   Symbol               Decimal

1 kilo ampere           1 k A                  1000 A

1 milli ampere          1 m A                  1/1000 A

1 micro ampere         1 µ A               1/1,000,000 A

current (I) =change in charge / change in time = dQ/dt

current measured by ampere . 1 Ampere = Coulomb /second

there are two types of current direct current (DC) and alternating current (AC)

DC is constant direction the flow of electrons in one direction

only .electrons flow from negative terminal to positive terminal

one the battery

                     I (DC) = Q/t

    AC change it`s polarity at half cycle and direction of 

electrons

                             I(AC)  =dQ/dt

         

SI system

                                               

                                             SI units

The system of units used in engineering and science is the (International system of units), usually abbreviated to SI units, and is based on the metric system and is now adopted by the majority of countries as .the official system of measurements 

 

The basic units in the SI system are listed with their symbols

length                                                           metre m

mass                                                            kilogram , kg

time                                                              second,     s

electric current                                              ampere , A

thermodynamic temperature                            kelvin, K

luminous intensity                                           candela, cd

amount of substance                                          mole, mol

    

     ·     SI units may be made larger or smaller by using prefixes which denote

multiplication or division by a particular amount. The six most common multiples, with their meaning, are listed

                    M   mega                multiply by 1 000 000    
        k    kilo                        multiply by 1000          
        m   milli                       divide by 1000           
             µ   micro                  divide by 1 000 000

         n  nano    divide by 1 000 000 000              

         p pico                    divide by 1 000 000 000 000