Electricity and Electrical Properties of Materials Lecture Notes PDF

Biophysics dept. Electricity and electrical properties of materials Dr.Rehab Abdel Sattar LECTURE OUTLINE Ohm’s law. Electrical properties of materials. Electrical conductivity of materials. Conductors, semiconductor s and insulators. Applications of electrical p...

Biophysics dept. Electricity and electrical properties of materials Dr.Rehab Abdel Sattar LECTURE OUTLINE Ohm’s law. Electrical properties of materials. Electrical conductivity of materials. Conductors, semiconductor s and insulators. Applications of electrical properties in dental medicine. LECTURE ILOs Student will be able to understand Ohm’s law. Student will be able to analyze the electrical properties of conductors,semi- conductors and insulators. Students will be able to apply the electrical properties on dental medicine.  Electromagnetic radiation High energy level Low energy level Ohm’s law Ohm’s law states that the voltage or potential difference between two points is directly proportional to the current or electricity passing through the resistance, and directly proportional to the resistance of the circuit. The formula for Ohm’s law is V=IR. This relationship between current, voltage and resister. Electrical properties of materials Electrical property refers to the response of a material to an applied electric field. One of the principal characteristics of materials is their ability (or lack of ability) to conduct electrical current. Indeed, materials are classified by this property, that is, they are divided into conductors, semiconductors, and nonconductors. Electrical conductivity of materials Electrical conductivity and its converse, electrical resistivity, is a fundamental property of a material that quantifies how it conducts the flow of electric current. Electrical conductivity or specific conductance is the reciprocal of electrical resistivity. The symbol for electrical conductivity is κ (kappa), and also σ (sigma) or γ (gamma). The SI unit of electrical conductivity is siemens per metre (S/m). A high conductivity indicates a material that readily allows the flow of electric current. Note that, electrical resistivity is not the same as electrical resistance. Electrical resistance is expressed in Ohms. While resistivity is a material property, resistance is the property of an object. Conductors- Semiconductors- Insulators Substances in which electricity can flow are called conductors. Conductors are made of high-conductivity materials such as metals, in particular copper and aluminium. Insulators, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance. Semiconductors are materials, inorganic or organic, which have the ability to control their conduction depending on  The name semiconductor comes from the fact that these materials have an electrical conductivity between that of a metal, like copper, gold, etc. and an insulator, such as glass. They have an energy gap less than 4eV (about 1eV). In solid- state physics, this energy gap or band gap is an energy range between valence band and conduction band where electron states are forbidden. In contrast to conductors, electrons in a semiconductor must obtain energy (e.g. from ionizing radiation) to cross the band gap and to reach the conduction band.  To understand the difference between metals, semiconductors and electrical insulators, we have to define the following terms from solid-state physics:  Conduction Band. In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level and thus determine the electrical conductivity of the solid. In semiconductors, the conduction band is the lowest range of vacant electronic states. On a graph of the electronic band structure of a material, the valence band is located below the Fermi level, while the conduction band is located above it. In semiconductors, electrons may reach the conduction band, when they are excited.  The distinction between the valence and conduction bands is meaningless in metals, because conduction occurs in one or more partially filled bands that take on the properties of both the valence and conduction bands. Band Gap. In solid-state physics, the energy gap or the band gap is an energy range between valence band and conduction band where electron states are forbidden. In contrast to conductors, electrons in a semiconductor must obtain to cross the band gap and to reach the conduction band. Band gaps are naturally different for different materials.  Fermi Level. The term “Fermi level” comes from Fermi-Dirac statistics, Fermi level is the term used to describe the top of the collection of electron energy levels at absolute zero temperature. Electron-hole Pair. In the semiconductor, free charge carriers are electrons and electron holes(electron-hole pairs). Electrons and holes are created by excitation of electron from valence band to the conduction band. An electron hole (often simply called a hole) is the lack of an electron at a position where one could exist in an atom or atomic lattice.  It is one of the two types of charge carriers that are responsible for creating electric current in semiconducting materials. Since in a normal atom or crystal lattice the negative charge of the electrons is balanced by the positive charge of the atomic nuclei, the absence of an electron leaves a net positive charge at the hole’s location. Positively charged holes can move from atom to atom in semiconducting materials as electrons leave their positions. When an electron meets with a hole, they recombine and these free carriers effectively vanish. The recombination means an electron which has been excited from the valence band to the conduction band falls back to the empty state in the valence band, known as the holes.  Electrical properties of human tissues: Tissues and organs exhibit electrical properties that we divide into passive and active: passive electrical properties’ – behavior of tissues in an electric field (conductivity, capacity), active electrical properties’ – electrical manifestations associated with the tissue’s own activity. Electrically Conductive tissues: Nervous tissues ( neurons) and muscles.  Human tissue consists of cells suspended in an aqueous medium. As a consequence, the electrical conductivity of a tissue is inhomogeneous on a microscopic scale. On a macroscopic scale the conductivity of a tissue can be considered to be homogeneous, and this conductivity is called the effective conductivity. The cells in the human body contain different ions like chlorine ion, potassium ion, sodium ion, which possess the tendency to conduct electricity. Ex.: sodium potassium pump.  Insulating components in human body: Enamel and dentin ( Carbonated hydroxyapatite+ Calcium). Applications of electricity and electrical properties in dental medicine Current adhesive systems follow either an "etch-and-rinse" or "self-etch" approach, which differ in how they interact with natural tooth structures. Etch-and-rinse systems comprise phosphoric acid to pretreat the dental hard tissues before rinsing and subsequent application of an adhesive. The use of electric current during application of etch-and- rinse adhesive systems has been recently introduced to decrease microleakage. Many studies investigated the effects of an electric field produced by an experimental device for the application of a two-step etch-and-rinse References: Introduction to the Electronic Properties of Materials – David C. Jiles · 2017 · Preview · https://books.google.com.eg/books?id=v_iF cKNo_N4C&pg=PA157&dq=electrical+cond uctivity+of+oral+tissues&hl=en&newbks= 1&newbks_redir=0&source=gb_mobile_sear ch&sa=X&ved=2ahUKEwiG-NCBoc6IAxX92 AIHHWXAGTQQ6AF6BAgNEAM Hermann Scharfetter, Robert Merwa · 2007 · Preview · More editions.