Quiz Study 9-14 Flashcards
Describe two techniques of cathodic protection to prevent the corrosion of metals
Galvanic Couple: the anodes connected to the protected structure have a natural potential that is more negative than the structure’s. When connected in a circuit, cathodic protection current flows from the anode (more negative) to the structure (less negative).
Impressed current Cathodic: Component to be protected is connected to power source. Impressed current flows from electrode to component to be protected.
Describe the differences in electronic band structures of metals, semiconductors, and
insulators.
Metals: overlapping valence gap, which allows conduction
Semi-conductors: filled valence band is separated from the empty conduction band by a small gap.
Insulators: Filled valence band is separated from the empty conduction band by a large gap.
Describe differences in the conductivity change with temperature between metals and
semiconductors
Semiconductors have a negative temperature
coefficient (they tend to increase their conductivity at higher temperatures), whereas metals have a positive temperature
coefficient (their conductivity is decreased at higher temperatures).
Describe three major functions of semiconductor devices.
P-N rectifying junction- is an electronic device that allows the current to flow in one direction only.
Transistors- Can amplify an electrical signal and serve as switching devices in computers for the processing and storage of information/
Microelectronic Circuitry- Large amount of electronic components and circuits are incorporated to a very small space.
Describe current flow in a p-n junction under forward and reverse bias.
Forward Bias- conducts a current once the barrier voltage is overcome.
Reverse Bias- a voltage across a diode in the opposite direction not easily.
Name three terminals of bipolar junction transistors and field-effect transistors.
Bipolar Junction Transistors- (E) Emitter, (B) Base, (C) Collector
Field Effect Transistors- (S) Source, (G) Gate, (D) Drain
Describe three different types of polarization
Electronic Polarization- Displacement of the center of the negatively charged electron cloud relative to the positive nucleus of an atom by the electric field
Ionic Polarization- An applied filed acts to displace cations i none direction and anions in the opposite direction, which gives rise to a net dipole moment.
Orientation Polarization- A rotation of the permanent moments in to the directions of the applied field.
Describe voltage output in response to external stress in piezoelectric materials.
Caused by a reconfiguration of the dipole-inducing surrounding or by re-orientation of molecular dipole moments under the influence of the external stress
Describe the concept of phonon
unit of vibrational energy that arises from oscillating atoms within a crystal
Describe thermal expansion in different materials in relation to bonding energy.
Metals- with high melting points (strong bonding) have low thermal expansion coefficients. Low melting point metals have high thermal expansion coefficients
Ceramics- strongly bonded have low thermal expansion coefficients
Polymeric- have large thermal coefficients & bonding is mostly covalent (Weaker)
Describe relationship between magnetic field strength (H), magnetic flux density
(magnetic induction) (B), and magnetization in magnetism (M
Magnetic field- amount of magnetising force
Magnetic flux density- amount of magnetic force induced on the given body due to magnetising force H
Magnetic Permeability- measure of the ability of a material to support the formation of a magnetic field within itself
Describe two origins of magnetic moments
Orbital Motion and its spin
Describe the differences in five magnetism in terms of magnetic moments with and
without magnetic field
Ferromagnet- Magnetic moments of equal magnitude arrange themselves in parallel to each other. (Permanent Magnets)
Ferrimagnet-the moments are unequal in magnitude and order in an antiparallel arrangement
Anti-Ferromagnetism- Moments are equal in magnitude and ordering occurs at a temperature called the neel temperature in an antiparallel to give no net magnetization.
Paramagnetism- weak form of magnetism observed in substances which display a positive response to an applied magnetic field
Diamagnetism- Materials that have a negative magnetic suceptability (repelled)
Describe hysteresis behavior in B-H curve of ferromagnetic materials.
Hysteresis loop shows the history dependant nature of magnetization of a ferro material. Once the material has been driven to saturation, the magnetization field can be dropped to zero and the material will retain most of its magnetization.
Describe the relationship between refractive index and speed of light in the material.
Refractive index of the medium is inversely proportional to the velocity of light in it. As the refractive index increases, the speed of light going through that medium decreases.
