PowerEase
®
300W Power Supply User Guide
17
4B
Appendix C
21B
Operational electrical parameters
48B
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)
49B
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.
50B
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.
51B
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.
52B
Power
The power in Watts, or the rate of heat generated by the system, is directly proportional to voltage
and current (P=IV).
