Callister - An introduction - 8th edition

770 • Chapter 18 / Electrical Properties
Equation Summary
• This polarization phenomenon accounts for the ability of the dielectrics to
increase the charge-storing capability of capacitors.
• Capacitance is dependent on applied voltage and quantity of charge stored
according to Equation 18.24.
• The charge-storing efficiency of a capacitor is expressed in terms of a dielectric
constant or relative permittivity (Equation 18.27).
• For a parallel-plate capacitor, capacitance is a function of the permittivity of the
material between the plates, as well as plate area and plate separation distance
per Equation 18.26.
• The dielectric displacement within a dielectric medium depends on the applied
electric field and the induced polarization according to Equation 18.31.
• For some dielectric materials, the polarization induced by an applied electric field
is described by Equation 18.32.
Types of Polarization
Frequency Dependence of the Dielectric Constant
• Possible polarization types include electronic (Figure 18.32a), ionic (Figure
18.32b), and orientation (Figure 18.32c); not all types need be present in a particular
dielectric.
• For alternating electric fields, whether a specific polarization type contributes to
the total polarization and dielectric constant depends on frequency; each polarization
mechanism ceases to function when the applied field frequency exceeds
its relaxation frequency (Figure 18.34).
Other Electrical Characteristics of Materials
• Ferroelectric materials exhibit spontaneous polarization—that is, they polarize in
the absence of an electric field.
• An electric field is generated when mechanical stresses are applied to a piezoelectric
material.
Equation
Page
Number Equation Solving for Number
18.1 V IR
Voltage (Ohm’s law) 721
18.2 r RA Electrical resistivity 721
l
18.4 s 1 r
Electrical conductivity 721
18.5 J se
Current density 722
18.6 e V Electric field intensity 722
l
18.8, 18.16
s nem e
Electrical conductivity (metal); conductivity for n-type
extrinsic semiconductor
727, 737
18.9 r total r t r i r d For metals, total resistivity (Matthiessen’s rule) 729
18.10 r t r 0 aT
Thermal resistivity contribution 729