PffpPossibleEssay2 - Pffp Possible Essays ELECTRICITY...

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Pffp Possible Essays 1 ELECTRICITY Electricity—movement of electrons Electric force—force electrons exert on other objects Units of measurement o Power: Watts o Current: Amps o Charge: Coulombs o Energy of e¯: Volts (eV) o Resistance: Ohms Electric current—movement of charged particles Property of Metals o Electrons can flow through solid inside of a metal o Electrons can’t leave surface of metal easily, because they’re attracted to positively-charged nuclei o Electric current flows in circles or closed paths o Electric cords require “return path” for electrons Resistance o As electrons move through wires, energy can be removed o Easiest way is by resistance—friction caused by electron flow o Conductors—materials that conduct electricity well (with little resistance) Most metals o Insulators—materials that don’t conduct electricity well Plastics, rock, wood o Semiconductors—materials that can turn from conductors to insulators Works by applying electricity a certain way In a tungsten light bulb o Current is 1 amp o Voltage is 110 volts o When current flows through it, resistance heats filament to make it glow current→ heat→ light In wires in home o Current is 15 amps o Wires made of copper, metal with low resistance Energy of electric current not wasted If high current, wires can be hot enough to start a fire o Fuses and circuit breakers make sure current does not exceed safe value, 15 amps o Fuses Short length of high-resistance material that melts when too much current flows through Breaks connection of wires when melts, and current stops flowing Must be replaced o Circuit-breakers Wire with bimetallic strip When it heats beyond allowed limit, it bends away Bending breaks the connection to another wire Can be reset after it has cooled
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Pffp Possible Essays 2 SUPERCONDUCTORS Superconductors—materials with zero resistance Known superconductors work only at low temperatures o Room temperature superconductor do not exist o Right now, energy wasted by conducting electricity through resistive wires Easiest way to cool wire is by putting it in cold liquid o Originally used liquid helium, which boils at 4 K (4° above absolute zero) Compounds that become superconductors at high temperatures o Highest temperature so far is 150 K Higher than temperature of liquid nitrogen, at 77K Nitrogen more abundant than helium Superconductors cooled by liquid nitrogen are more practical o Not used in power transmission because brittle, and hard to make wire from these o Limit to amount of current that superconducting wires can carry High current creates strong magnetic fields Strong magnetic fields can destroy superconductivity Electrons flow through a metal with zero friction VOLTS and ELECTRON ENERGY Volts o Calorie is typical amount of chemical energy for gram of material; eV is typical amount of energy for
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PffpPossibleEssay2 - Pffp Possible Essays ELECTRICITY...

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