Lecture

Capacitance and Dielectrics: Polarization Mechanisms

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In course

PHYS-201(d): General physics : electromagnetism

The topics covered by the course are concepts of electromagnetism, properties of waves, and fluid mechanics. ...

Description

This lecture covers the concepts of capacitance, dielectrics, and polarization mechanisms in materials. It starts by defining capacitance for plate capacitors and explaining the energy stored in them. The role of dielectrics in technical capacitors is discussed, highlighting the structure of a wound cell capacitor. The lecture then delves into the polarization of matter by electric fields, introducing the concept of an electric dipole moment and the polarization mechanisms in different materials such as glass, water, and NaCl. By the end of the lecture, students will understand how electric fields polarize insulators, the formation of electric dipole moments, the definition of dielectrics, and the evaluation of potential functions and electric fields of dipole moments.

Instructor

Dirk Grundler

Official source

Related concepts (32)

Polymer capacitor

A polymer capacitor, or more accurately a polymer electrolytic capacitor, is an electrolytic capacitor (e-cap) with a solid conductive polymer electrolyte. There are four different types: Polymer tantalum electrolytic capacitor (Polymer Ta-e-cap) Polymer aluminium electrolytic capacitor (Polymer Al-e-cap) Hybrid polymer capacitor (Hybrid polymer Al-e-cap) Polymer niobium electrolytic capacitors Polymer Ta-e-caps are available in rectangular surface-mounted device (SMD) chip style.

Aluminum electrolytic capacitor

Aluminum electrolytic capacitors are polarized electrolytic capacitors whose anode electrode (+) is made of a pure aluminum foil with an etched surface. The aluminum forms a very thin insulating layer of aluminum oxide by anodization that acts as the dielectric of the capacitor. A non-solid electrolyte covers the rough surface of the oxide layer, serving in principle as the second electrode (cathode) (-) of the capacitor. A second aluminum foil called “cathode foil” contacts the electrolyte and serves as the electrical connection to the negative terminal of the capacitor.

Electrolytic capacitor

An electrolytic capacitor is a polarized capacitor whose anode or positive plate is made of a metal that forms an insulating oxide layer through anodization. This oxide layer acts as the dielectric of the capacitor. A solid, liquid, or gel electrolyte covers the surface of this oxide layer, serving as the cathode or negative plate of the capacitor. Because of their very thin dielectric oxide layer and enlarged anode surface, electrolytic capacitors have a much higher capacitance-voltage (CV) product per unit volume than ceramic capacitors or film capacitors, and so can have large capacitance values.

Capacitor types

Capacitors are manufactured in many styles, forms, dimensions, and from a large variety of materials. They all contain at least two electrical conductors, called plates, separated by an insulating layer (dielectric). Capacitors are widely used as parts of electrical circuits in many common electrical devices. Capacitors, together with resistors and inductors, belong to the group of passive components in electronic equipment.

Tantalum capacitor

A tantalum electrolytic capacitor is an electrolytic capacitor, a passive component of electronic circuits. It consists of a pellet of porous tantalum metal as an anode, covered by an insulating oxide layer that forms the dielectric, surrounded by liquid or solid electrolyte as a cathode. Because of its very thin and relatively high permittivity dielectric layer, the tantalum capacitor distinguishes itself from other conventional and electrolytic capacitors in having high capacitance per volume (high volumetric efficiency) and lower weight.

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