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Transcript

Electrostatics Quantities & Concepts Charge (charge conservation) Electrostatic Potential Energy Electrostatic Force Electrostatic Potential Electric Field Electric Field Lines Electric Flux Gauss’ Law ◦ Potential ◦ Voltage ◦ Electromotive Force (EMF) Charge Electrostatic Force Coulombs Law - + + “sames” repel + “opposites” attract Electric Field Coulombs Law The “field point” is a location of the “system” (aka, “the object of interest”). The “surroundings” creates “electric field” and the system (to be located at the field point) feels the effect + Charge in the “surroundings” is associated with the “electric field” (the surrounding charge creates the electric field) Electric Field Lines + “Electric Field Lines” are a visual pattern generated by considering the force a “positive test charge” would feel if placed at various locations. Electric Flux “Electric Flux” is electric field times area (but only the field component perpendicular to the area. If the area is a closed surface then flux is positive if field is leaving the enclosed volume. Flux is negative if the field is entering the enclosed volume. Gauss’ Law 𝑞′ Φ= 𝜖0 q‘ is the charge inside the closed surface The total electric flux for a closed surface is proportional to the charge enclosed. Gauss’ Law Examples Point Charge and charge distributions with spherical symmetry. Infinite “sheet” of charge 𝜎 𝐸= 2𝜖0 + Parallel Plate Capacitor 𝜎 𝐸= 𝜖0 𝑘 𝑞′ 𝐸= 2 𝑅 q’ is charge inside your radius σ is charge density + − on positive plate Potential Energy & Potential final 𝑞 initial Δ𝑈 Δ𝑉 = 𝑞 System is moved from initial to final. Electrostatic force does work. This work is “conservative” so we can define “potential energy”, Δ𝑈 = −𝑊 = +𝑊𝑎𝑔𝑒𝑛𝑡 “potential” is potential energy divided by system charge. Joules per coulomb is volts Potential for point source charge Coulombs Law R q 𝑘𝑞 𝐸= 2 𝑅 𝑘𝑞 𝑉= 𝑅 Potential for uniform field V1 V2 E E is constant High Volts Low Volts d Δ𝑉 𝐸= 𝑑 Electric field goes from high to low volts. A newton per coulomb is a volt per meter.