Appendix C
Operational electrical parameters
Ohm’s Law and
Joule’s Law
Electrophoresis is the migration of a charged particle under the influence of an electrical
field. The power supply output parameters voltage, current, and power are related by the
following two equations:
Voltage (V) = Current (I) x Resistance (R); (V=IR)
Power (P) = Current (I) x Voltage (V); (P=IV)
Resistance
Resistance of the assembled electrophoresis cell is dependent on the conductivity of the
gel buffer, the thickness of the gel, and the number of gels being run. Although the
resistance is determined by the gel system, the resistance can vary over the course of an
electrophoretic separation. For instance, in the Tris-Glycine buffer system, the fast
moving, highly conductive chloride ions in the gel are gradually replaced by the slower
moving, less conductive glycine ions from the running buffer as the gel runs. As a result,
the resistance of the gel increases as the chloride/glycine front moves down the gel.
Voltage
The velocity with which an ion moves in an electric field will vary in proportion to the
field strength (volts per unit distance). The higher the voltage the faster an ion will move.
Current
Current is a function of the number of ions passing a given cross-section of the circuit at a
given time. For a given gel/buffer system, at a given temperature, current will vary in
proportion to the field strength (voltage) and/or cross-sectional area (number and/or
thickness of the gels). Ions in solution and at a given voltage will move faster as the
temperature increases, increasing current.
Power
The power in Watts, or the rate of heat generated by the system, is directly proportional
to voltage and current (P=IV).
PowerEase
®
90W Power Supply User Guide
15
Summary of Contents for PowerEase 90W
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