Moving-electron and stationary-molecule interactions oppose electric current flow {resistance}| and turn electric energy into heat. Electrical resistance depends on path length, cross-sectional area, and material resistivity.
voltage
Resistance makes heat from electrical kinetic energy and, as potential energy decreases, drops potential across resistor.
current
For same voltage, more resistance makes less current, because flow slows.
factors
Resistance is more for poor conductors with few electrons that can move, for longer conductor length, or for less cross-sectional area. If cross-sectional area is more, conductor perimeter is more, fewer electron collisions happen, and resistance is less. If conductor length is more, distance is longer, and total resistance is more. If material resistivity is more, conductor has fewer free charges, and resistance is more.
factors: temperature
In conductors at higher temperature, resistance is more, because random motions are more. In insulators or semiconductors at higher temperature, resistance is less, because more electrons are free to move. Alloys have smaller resistance change when temperature changes, because alloys have fewer free electrons than pure metals.
resistor
Electrical devices {resistor} can have resistance. Conductor resistance R equals material resistivity r, which differs at different temperatures, times conductor length l divided by conductor cross-sectional area A: R = r * l / A.
resistivity
Resistivity is 10^-6 to 10^-1 ohm-cm for conductors, 10^-1 to 10^8 ohm-cm for semiconductors, and 10^8 to 10^21 ohm-cm for insulators.
examples
Resistance in incandescent light bulbs creates light. Resistance in electric heaters creates heat. Fuses, circuit breakers, voltmeters, ammeters, tube resistors, rod resistors, and coil resistors demonstrate electrical resistance. Lie detectors detect skin electrical resistance, which varies with sweat amount.
Physical Sciences>Physics>Electromagnetism>Conductivity
5-Physics-Electromagnetism-Conductivity
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Date Modified: 2022.0224