Electrical polarization describes how materials react to an electric field. It involves a realignment of electrical charges within a material, creating a temporary imbalance of positive and negative charge centers. This internal shift differs from continuous electrical current. Understanding polarization reveals how substances behave electrically, enabling technological advancements.
Defining Electrical Polarization
Electrical polarization occurs primarily in dielectric materials, which are electrical insulators. When an external electric field is applied to a material, the positive and negative charge centers within its atoms or molecules experience opposing forces. This causes a slight separation of these charge centers, even though charges are not free to move throughout the material. This internal displacement of charges creates numerous tiny electric dipoles within the material.
The collective effect of these microscopic dipoles is the formation of an internal electric field that opposes the original external field. This internal field effectively reduces the net electric field within the dielectric material.
Unlike electrical conduction, where charges flow freely, polarization involves localized shifts within the atomic or molecular structure, maintaining the material’s insulating properties.
The Mechanism of Material Polarization
Materials become polarized through several microscopic mechanisms, depending on their atomic and molecular structure. Electronic polarization occurs in all materials.
An electric field distorts the electron cloud around an atomic nucleus, shifting its negative charge center relative to the positive nucleus. This distortion effectively stretches the atom into a tiny dipole.
Orientational polarization is prominent in materials with polar molecules, such as water. These molecules inherently possess a permanent electric dipole moment due to their asymmetrical charge distribution. When an external electric field is applied, these pre-existing dipoles rotate and align with the field. This alignment of numerous molecular dipoles contributes to the overall polarization of the material.
Polarization in Everyday Life
Electrical polarization is responsible for several observable phenomena in daily life. A common example is static cling, often experienced after clothes come out of a dryer. Friction during drying transfers electrons between fabrics, creating charged areas. When these oppositely charged fabrics come close, the electric field from one induces polarization in the other, causing them to stick together.
Similarly, when a charged balloon sticks to a wall, it demonstrates the effect of induced polarization. Rubbing a balloon on hair gives it a net charge. When brought near a neutral wall, the balloon’s charge repels like charges within the wall’s atoms and attracts opposite charges, inducing localized dipoles in the wall. This induced polarization creates an attractive force that allows the balloon to adhere to the surface.
Dust attraction to television or computer screens also occurs due to polarization. The static charge on the screen induces polarization in dust particles, drawing them to the display.
Applications in Technology
Electrical polarization is harnessed in various technological applications. Capacitors, which store electrical energy, utilize dielectric materials that undergo polarization.
The polarized dielectric between a capacitor’s conductive plates enhances its ability to store charge at a given voltage. This polarization allows capacitors to accumulate and release electrical energy efficiently.
Liquid crystal displays (LCDs) also rely on polarization. Liquid crystal molecules are naturally polar and align with an electric field. In LCD screens, electric fields control their orientation, manipulating light passage to create images. Piezoelectric sensors convert mechanical stress into electrical signals, a process rooted in polarization changes. Certain crystals exhibit piezoelectricity, where mechanical deformation induces charge separation and polarization, generating an electrical voltage.