Definitions

Material copyright 1993 by M. Gore.  All rights reserved.

This is a list of basic electronic terms used in 
electronics class.

RESISTANCE: The ability of a material to 
OPPOSE current flow.  All materials have some 
resistance.  Measured in OHMS for electronics.

CONDUCTORS: The ability of a material to 
ALLOW current flow.  All materials have some 
conductivity.  Measured in MHOs.  The opposite 
of OHMs.

VOLTAGE:  A term used to describe the "force" 
that causes current to flow in a conductor.  
Also know as "Electromotive Force (EMF). The 
symbol is V.

CURRENT: The flow of electrons in a conductor.

AMP:  6.28 x 10 to the 18th power
electrons past a point in one 
second. That's
  6,280,000,000,000,000,000 electrons !!!
The symbol is I. 

OHM: The resistance of 1,000 feet of #10 gauge 
copper wire is 1 ohm.  The unit of resistance. 
The Symbol is the Greek ohm.

 VOLT: The "pressure" or "Force" to get 1 amp 
through 1 ohm is 1 volt. The symbol is V.

OHM's LAW:  Voltage is equal to Current times 
Resistance. V = IR

POWER: The amount of "Work" the circuit does.  
For a resistor it is heat.  

WATT: The unit of electrical power.  Voltage 
times Current equals Wattage (if both are in 
phase with each other). P = VI

MAGNETIC FIELD: The invisible magnetic force 
that surrounds a magnet or is created when a 
current travels through a wire.

COIL: A simple wrapping of many turns of a wire 
close together to intensify a magnetic field 
created when a current passes through the wire.  
Measured in units of HENRYs. Causes a shift in 
phase between voltage and current. Stores energy 
in a magnetic field.  Opposes changes in 
voltage.  It INCREASES its' IMPEDANCE to voltage 
changes as frequency goes HIGHER.  It does pass 
DC. 
 


IMPEDANCE: The TOTAL opposition to current 
flow.  Unlike pure resistance, Impedance takes 
into account phase relationships between voltage 
and current, and frequency as well as pure 
resistance.  Still measured in units of OHMs. 
The symbol is Z.

CAPACITANCE: A current storage device.  2 
plates are separated close but away from each 
other and hold current by electrostatic charge.  
Opposes a change in current by storing current, 
and then feeding this stored current out when 
the supplied current is low.  Blocks DC voltage 
and current.  Changes its' IMPEDANCE as 
frequency changes.  IMPEDANCE goes LOWER as 
frequency INCREASES.  Also causes a phase shift! 
Measured in units of Farads.

DIODE: Consider this a "one-way current 
switch".  It allows current flow in one 
direction only. Must have .6 volts to "turn on". 

FILTER: A circuit that changes its' impedance 
with frequency changes.  It allows some 
frequencies to pass while blocking or reducing 
others.

TRANSISTOR: A three terminal device (three 
connections), basic amplifier.  A small change 
in BASE current causes a large change in 
COLLECTOR current and voltage.  Two basic types, 
NPN and PNP.  Almost always silicone.

OP-AMP: A pre-made complex circuit in a simple 
to use package.  It amplifies the difference 
between its' two input terminals via a simple 
mathematical formula: the FEEDBACK impedance 
divided by the INPUT impedance.

NOISE: Unwanted signals.  Usually refered to as 
hiss, though includes distortion too.  Lowest 
noise possible: -128.5 dbm at room temperature.

AMPLIFICATION: When a small change in current 
and/or voltage causes a larger change in BOTH 
current and voltage (WATTAGE)in the output.  Can 
also refer to a large change in just voltage, 
though an increase in wattage is the correct way 
to look at this term.

DECIBEL: 1/10 bel.  One BEL is "twice-as-loud" 
to most people.  A logrymithic relationship 
between powers (Watts), or voltages.  DBm is 
decibels measured with 600 ohms at the output 
device: a audio standard.  DBv is measured into 
a high-impedance, usually 10,000 ohms.  0dbm = 
.775 volts rms. into 600 ohms.  Most pro audio 
is set up so the output of a device at 0VU is 
equal to +4dbm.  Semi-pro gear uses -10dbv.