VOLTAGE:
The driving force for charged particles.
Measured in volts.
|
| CURRENT:
The flow of charged particles past a
given point per unit time. Positive
Current flows from Positive to Negative.
Measured in "milliamps" (mA). |
IMPEDANCE:
A substance that impedes the flow of
current (skin, fat etc.) Sometimes
referred to as "resistance".
Measured in "ohm's".
Ohm's Law: Current = Voltage/Impedance
|
| Constant
Voltage - The ability of a
device to keep it's current constant over
any load resistance. Higher impedance
will lower current. Lower impedance will
higher current. |
Constant
Current - The ability of a
device to keep it's voltage constant over
any load resistance. Higher impedance
will lower voltage. Lower impedance will
higher voltage.
(So Patients will not recognize change in
intensity as impedance changes)
|
| HIGH
IMPEDANCE |
LOW
IMPEDANCE |
| Skin |
Extracellular
Fluid |
| Adipose
Tissue (FAT) |
Intracellular
Fluid |
| Blood
Vessel Walls |
Blood |
| Nerve
& Muscle Fiber Membranes |
Sweat |
|
TYPES OF CURRENT
Alternating Current:
Current that flows in one direction then
reverses. Therefore the waveform has two
phases with zero net DC.
Direct Current: Current
that has no change in the direction of
flow.
|
| |
