DC electronics

Resistance Because electrons have mass and are held in place by polarity “bonds” – energy is consumed to dislodge electrons Resistance is affected by – Composition of material – Length of material – Cross-sectional area of material – Temperature of material

Resistance Composition – Resistance is the opposite of conductivity so resistance is lowest in silver, gold, copper, etc. Length – Resistance increases as length increases – Causes voltage drop in long cables Cross-sectional area – Resistance increases as cross section decreases – Causes heating of under-sized cables

Resistance Cross-sectional area – Wire diameter is described by system of “gauges” called American Wire Gauge (AWG) – Bigger number equals smaller diameter 28 is used for telephone, 12 or 14 is for household current, 00 is for entrance cable, etc Temperature – As temperature increases, so does resistance – “Super conductors” are cooled to absolute zero

AC versus DC +120 Volts -120 Volts 0 Volts +12 Volts -12 Volts 0 Volts

Capacitance There is a field of force surrounding the electrons Current can be caused to flow even when there is a “break” in a circuit When enough electrons, or negative force, build up – adjacent electrons can be caused to move

Capacitance Capacitors are constructed of two plates in close proximity Plates are separated by an insulator called a dielectric Current can flow through a capacitor even though the plates are separated by an insulator

Capacitance Plate Dielectric

_ Capacitance Plate Dielectric _ _ _ _ _ _ __ _ _ _ _

Capacitors Capacitors have the ability to store electrons The quantity of electrons in a capacitor is measured in farads Farad is the measure of capacitance 1 farad = 6.28 X 10 Size of plates and the dielectric constant determine capacitance 18

Capacitors Dielectric made be made of – Wax paper – Ceramic – Mylar – Mica – Electrolyte – Air (

Capacitors One application of capacitors is to convert AC to DC During each phase of AC when electrons are pushed onto the “in” plate – some current flows off the “out” plate During the opposite phase when no electrons are moving into capacitor – no current flows out

Capacitors Output current from a capacitor + _

Capacitors