* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Electricity
Survey
Document related concepts
Fundamental interaction wikipedia , lookup
Electron mobility wikipedia , lookup
Introduction to gauge theory wikipedia , lookup
Magnetic monopole wikipedia , lookup
Field (physics) wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Electromagnetism wikipedia , lookup
Aharonov–Bohm effect wikipedia , lookup
Nuclear physics wikipedia , lookup
Maxwell's equations wikipedia , lookup
Elementary particle wikipedia , lookup
Electrical resistivity and conductivity wikipedia , lookup
Lorentz force wikipedia , lookup
Atomic nucleus wikipedia , lookup
Transcript
Electricity Click this link Lightning • Stepped Leader: Path of ionized air. – large number of quick jumps, each up to 50 meters long. – branch into a number of paths. – takes (100’s of milliseconds) to descend. – almost invisible compared • Positive Streamers arise as the leader approaches the ground due to the intense electric field created by the approaching leaders. • circuit is closed, and the main lightning stroke follows with much higher current. • Negative lightning contains a number of re-strikes along the same channel creating a strobe effect. Lightning • Positive – - 300 kiloamperes of current (10 times more current than neg. lightning) – transfers a charge of up to 300 coulombs – potential difference up to 1 gigavolt – lasts for hundreds of milliseconds – discharge energy of up to 3x1011joule. Lightning • No, no, no. This sucker's electrical, but I need a nuclear reaction to generate the 1.21 gigawatts of electricity I need. What is Electrical Charge? • There are two types of electric charges – positive charges – negative charges • LIKE charges REPEL each other. (positive-positive; negative-negative) • UNLIKE charges ATTRACT each other (positive-negative) Electric Forces + Opposites charges attract + - - Fundamentals of Electricity • Protons carry a fundamental positive charge. Proton Quarks – Baryon (3 quarks) • Electrons carry a fundamental negative charge. Electron Lepton +1 (+⅔ +⅔ -⅓) u u d -1 – Leptons • Neutrons carry no net charge. Neutron Quarks 0 (+⅔ - ⅓ - ⅓) u d d Atomic Structure ? • Protons, neutrons and electrons are found within atoms • Protons are in the center with neutrons and are tightly bound in the nucleus • Electrons, however, are much smaller and move around the nucleus, and therefore, can be easily lost or gained. • Therefore, when a negative charge is gained (-) electrons are gained, and when a positive charge is gained (+) electrons are lost How is Charge Measured? • The unit of charge in the SI system of measurement is the coulomb (C) • The charges of protons and neutrons are denoted as (e) elementary charges • 1 elementary charge is 1.6 x 10-19 C. • 1 coulomb (C) = 6.25 x 1018 elementary charges. Fundamentals of Electricity Proton • The proton has a positive elementary charge. Electron • The electron has a negative elementary charge. • The neutron has a net Neutron charge of zero. + 1.6 x 10-19 C - 1.6 x 10-19 C 0 Q is the charge of object (in coulombs) e is the elementary charge Q = ne n is the number of elementary charges How many excess electrons are on an object with a charge of - 8.0 x 10-19 C Q = ne Transfer of Electric Charge • Materials with a mobile sea of free electrons, are called conductors. – Metals, 1028 /m3 • Materials with few free electrons are called insulators – rubber, silk, glass, plastic Law of conservation of Charge During any charging process or interaction between matter the net charge of the system must remain constant. Electrification by Friction • Two neutral objects (ex. hair and balloon) are rubbed together 0 - 5pC + 5pC 0 Electrons are transferred from one object to another, resulting in equal magnitude, but opposite, charges. Charge by Contact • A Negatively charged sphere touches a positive sphere of the same surface area. - 18pC + 4 pC -7pC + 7pC Electrons are transferred from the sphere with more negatives to the sphere with less negatives, resulting in equal magnitude of Charge. Charge by Contact • A Negatively charged rod touches a neutral electroscope. Electrons are transferred from the rod with more negatives to the device with less negatives. The leaves of the scope acquire a negative charge and repell. Charging by Induction • A Negatively charged rod is brought near a neutral sphere. The Electrons charged are rod forced is removed from and the theleft net side positive of charge the sphere is re-to the distributed right side, charge separation A Ground connection is made. And the electrons “escape” to ground, neutralizing the right side of the sphere. Charging by Induction • A neutral conducting plate is brought near a negatively charged insulator plate. Electrons The plateare is removed forced from andthe the bottom net positive of the charge conductor is reto distributed the top side. charge separation A Ground connection is made. And the electrons “escape” to ground, neutralizing the top side of the plate. • Using two metal spheres and a charged object, how could you charge one sphere positive and one negative? Answer Electric Forces + Opposites charges attract + - - Coulomb’s Law • Between two point charges the force of attraction is proportional to the product of the two charges and inversely proportional to the square of the distance between them. r q1 q2 Force of repulsion is equal in magnitude on both charges regardless of the charge. Coulomb’s Law • • F = kq1q2 /r2 k = 8.99 x 109 Nm2/C2 Electrostatic constant • Click on Link Above for Example. r q1 q2 Force of repulsion is equal in magnitude on both charges regardless of the charge. The Electric Field The Electric Force per unit charge, where the test charge is a positive point charge. E = F/q + + TEST CHARGE Electric Field is a vector quantity The Electric Field around a point charge obeys an INVERSE SQUARE LAW E = kq/r2 E = F/q The Electric Field + + Field lines point away from positive charges Electric Field Rules + test charge Directed away from positive Line Density shows relative field strength Start and end on surface of a conductor at 90o + Field lines never cross Electric Potential Electric Field lines Electric potential lines form right angles with Electric lines of force. Electric potential is the Energy per unit charge. V = W/q + Equipotential lines Electric Potential is a Scalar quantity Electric Potential Electric Field lines Equipotential lines around a point charge form right angles with Electric lines of force. + Equipotential lines V = W/q Electric Potential is a Scalar quantity Electric Potential Energy • W = F d, • U = kq1q2 /r r q1 q2 The potential energy stored in the system of both charges regardless of the charge. Electric Potential Energy • W = F d, • U = kq1q2 /r r q1 q2 The potential energy stored in the system of both charges regardless of the charge. Electric Field Formulas • F = kq1q2 /r2 • U = kq1q2 /r • E = kq/r2 • V = kq/r • E = F/q • V = W/q Vectors Scalars E = V/d Experiments Faraday’s Cage - Shielding • An external electrical field causes the charges to rearrange which cancels the field inside. Coaxial Cables • Wire mesh is grounded. • Copper wire is shielded. Faraday’s Cage - Shielding • Airplanes act as Faraday cages, protecting passengers from lightning strikes. Millikan's Oil Drop Experiment • Showed the existence of an elementary charge • Click Link