16.4. Dielectrics http://www.ck12.org
16.4 Dielectrics
Objectives
The student will:
- Understand what a dielectric is and how it affects the capacitance of a capacitor.
- Solve problems involving capacitors with dielectrics.
Vocabulary
- dielectric constant:The factor by which the dielectric increases the capacitance. The dielectric constant is
particular to each dielectric material. - dielectric material:An insulating material placed between the conducting plates of a capacitor.
- polarization: A process similar to induction, in which the molecules of the inductor align such that the
positive end of the molecules will be attracted to the negative conducting plate and the negative end of the
molecules will be attracted to the positive conducting plate. An electric field is created inside the dielectric
that is opposite to the electric field between the two conducting plates of the capacitor.
Introduction
We mentioned earlier that electrostatic repulsion can cause an electrical breakdown or discharge across the plates of
a capacitor. Generally, this is not something that we wish will happen. We also mentioned that the capacitance was
dependent upon the physical dimensions of the capacitor and the insulator placed between its plates. The insulator
is called adielectric material,Figure16.12. We now investigate how the capacitance is affected by a dielectric.
Dielectrics
As we have just mentioned, a dielectric material is an insulating material inserted between the conducting plates of
a capacitor.
Let us consider the effect of inserting a dielectric between the plates of a charged capacitor. We assume the capacitor
is charged and then disconnected from the charging source (a battery, for example),Figure16.13.
A process similar to induction occurs, calledpolarization. When an insulator is inserted between the conducting
plates of the capacitor, the molecules of the inductor will align such that the positive end of the molecules will be
attracted to the negative conducting plate and the negative end of the molecules will be attracted to the positive
conducting plate, seeFigure16.14. An electric field is therefore created inside the dielectric that is opposite to the
electric field between the two conducting plates of the capacitor,Figure16.15.