Engineering 45. Electrical Properties-3. Bruce Mayer, PE Registered Electrical & Mechanical Engineer BMayer@ChabotCollege.edu. Learning Goals – Dielectrics. Understand the fundamentals of Electrical Capacitance How Certain Materials can Dramatically Increase the Electrical Capacity
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Bruce Mayer, PE
Registered Electrical & Mechanical EngineerBMayer@ChabotCollege.edu
Consider Two Conductive Plates Separated by a Small & Empty Gap With a Voltage Applied (right)
Since No Current Can Flow Across The Gap
Positive Charges Accumulate on Top
Negative Charges Accumulate on BotElectrical Capacitance
The Value of C can Found from an Expression that is Analogous to Ohm’s EqnElectrical Capacitance cont.
Introducing a Analogous to Ohm’s EqnConstant of proportionalitybetween C & A/ℓElectrical Capacitance cont.2
For a DiElectric Filled Cap Analogous to Ohm’s EqnElectrical Capacitance cont.3
Electric Field is the ratio of a Voltage Drop to Distance over Which the Drop Occurs; to whitElectrical Terms
and Current will Flow
What is a “DiPole”? over Which the Drop Occurs; to whit
DiPole Refers to the Physical SEPARATION of TWO, OPPOSITE-polarity, and thus Attractive, “Charge Entities”
Two Classical Types
“+” & “-” Charges SeparatedElectric DiPole
Not Aligned →Torque
Aligned →NO Torque
The Areal Density of Charges on Each Plate, DField Vectors cont.2
Consider Two Caps: One in a Vacuum, and one with a Dielectric Material Between the PlatesOrigins of DiElectric Constant
Note that Regions Removed from the Dielectric Surface Do Not Contribute to the ElectroStatic Balance, and thus this region is Electrically NEUTRAL
The Dielectric Surface Charge Tends to Cancel the Vacuum Charge
Hence the Battery Must Supply added Charge to Bring the interface Regions to Electrical Neutrality
This Occurs withOUT an increase in V; and to the Q/V quotient (C) increases
Quantify the Increase in D asOrigins of DiElectric Const cont.
Electronic Contribute to the ElectroStatic Balance, and thus this region is Electrically NEUTRALPolarization Types
Ionic Contribute to the ElectroStatic Balance, and thus this region is Electrically NEUTRALPolarization Types cont.
AC Electric signals Are often Applied at High Frequencies to Capacitive Materials
Since Dipole Alignment MUST have some FINITE Relaxation Time, r, Expect some Dielectric Frequency Dependence Frequency Dependence