Electrical Conduction and Resistance

Electrical conduction in materials refers to the ability of a material to allow the flow of electric charge, primarily carried by electrons, ions, or both.

Conductors, insulators, and semiconductors.

<p>They have conductivity between conductors and insulators.</p> Signup and view all the answers

<p>Resistivity is a property of a substance that describes its opposition to the flow of current through it.</p> Signup and view all the answers

<p>All of the above</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>The resistance of a material is directly proportional to its length, meaning resistance increases with increasing length and decreases with decreasing length.</p> Signup and view all the answers

<p>The resistance of a material is inversely proportional to its cross-sectional area, meaning resistance increases with decreasing cross-sectional area and decreases with increasing cross-sectional area.</p> Signup and view all the answers

<p>The resistance of a substance is directly proportional to the resistivity of the materials it's made from.</p> Signup and view all the answers

<p>The resistance of a metallic conductor increases with increasing temperature.</p> Signup and view all the answers

<p>Resistivity is the electrical resistance of a conductor of unit cross-sectional area and unit length. It is a characteristic property of each material, providing a useful basis for comparing various materials on their ability to conduct electric currents.</p> Signup and view all the answers

<p>Materials with stable temperature coefficients of resistance are ideal for precision applications as they maintain their resistance values reliably over a wide range of temperatures.</p> Signup and view all the answers

<p>Resistive materials must withstand mechanical stress without degrading, ensuring their structural integrity and maintaining their resistance properties.</p> Signup and view all the answers

<p>Stability refers to the ability of resistive materials to maintain their resistance values under varying conditions, such as temperature and load, ensuring reliable performance in diverse environments.</p> Signup and view all the answers

<p>Fixed resistor</p> Signup and view all the answers

<p>Variable resistor</p> Signup and view all the answers

<p>Metal film resistors</p> Signup and view all the answers

<p>Wire-wound resistors</p> Signup and view all the answers

<p>A thermistor is a resistor whose resistance changes with temperature. A common application is in temperature sensors for HVAC systems.</p> Signup and view all the answers

<p>A photoresistor is a resistor whose resistance varies with light intensity. A common application is in automatic street lights.</p> Signup and view all the answers

<p>All of the above</p> Signup and view all the answers

<p>The temperature coefficient of a resistor indicates the fractional change in resistance per degree Celsius (°C). It is typically expressed in parts per million (ppm).</p> Signup and view all the answers

<p>The frequency response of a resistor describes how it behaves at different frequencies of alternating current (AC) signals, indicating whether it still acts as a pure resistor or if it exhibits characteristics of capacitance and/or inductance.</p> Signup and view all the answers

<p>Power dissipation refers to the maximum power a resistor can handle without overheating. It is crucial in selecting a resistor to ensure its resistance value remains stable and the device does not fail due to excessive heat buildup.</p> Signup and view all the answers

<p>Power de-rating is a reduction in the maximum power a resistor can handle at higher temperatures. As temperature increases, the ability of the resistor to dissipate heat decreases, leading to a reduced power rating.</p> Signup and view all the answers

<p>The maximum temperature rating indicates the upper temperature limit at which the resistor can function reliably. Exceeding this limit can lead to damage or failure of the resistor.</p> Signup and view all the answers

<p>The maximum voltage rating indicates the maximum voltage across the resistor beyond which the electrical stress can cause it to fail or break down. A voltage flash-over or a sudden breakdown of the resistor can occur if the voltage rating is exceeded.</p> Signup and view all the answers

<p>Selecting an appropriate resistor requires considering resistance value, power rating, tolerance, temperature coefficient, voltage rating, mounting type, special conditions, material and construction type, and ensuring safety compliance.</p> Signup and view all the answers

<p>Standardized resistance values, known as preferred values, are used for practical reasons and to simplify resistor selection and manufacturing.</p> Signup and view all the answers

<p>Resistors with a low TCR maintain stability and accuracy, particularly in conditions with fluctuating temperatures.</p> Signup and view all the answers

<p>Exceeding the voltage rating can lead to breakdown or failure of the resistor under high-voltage conditions.</p> Signup and view all the answers

<p>Surface-mount technology offers advantages such as reduced size, increased component density, and automated assembly, making it suitable for high-density electronic circuits.</p> Signup and view all the answers

<p>Through-hole mounting is a more robust and reliable technology, making it well-suited for handling higher power levels and ensuring long-term stability.</p> Signup and view all the answers

<p>Special conditions include high-frequency applications, pulse power applications, environmental factors, and specific material and construction requirements.</p> Signup and view all the answers

<p>Space suits utilize materials that are lightweight, durable, and capable of providing protection from extreme environments, including radiation, micrometeoroids, and temperature variations. Examples include Kevlar, Nomex, polycarbonate, Vectran, Teflon, and coated Teflon.</p> Signup and view all the answers

<p>UV radiation can cause fading, strength loss, and brittleness in materials over time, particularly for organic polymers.</p> Signup and view all the answers

<p>UV stabilizers, including absorbers and HALS, are incorporated into organic polymers to prevent damage by absorbing UV radiation and releasing it as heat.</p> Signup and view all the answers

<p>Fire-resistant clothing, also known as turnout gear, is designed to protect firefighters from extreme heat and flames, as well as other hazards. Common materials include Nomex, Kevlar, Modacrylic, and PBI, all of which possess excellent thermal stability, flame resistance, and heat protection properties.</p> Signup and view all the answers

<p>Firewalls serve as passive fire protection systems, containing fires and preventing their spread within a building. Common materials used in firewalls include concrete, gypsum board, brick, steel (with fireproofing), and modular wall systems.</p> Signup and view all the answers

<p>Advanced materials used in firewalls that enhance thermal resistance include fire-resistant insulation (mineral wool) and advanced ceramics (such as FIBERFRAX).</p> Signup and view all the answers