# 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.

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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.electric field 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 coulombscoulombs –potential difference up to 1 gigavolt –lasts for hundreds of milliseconds –discharge energy of up to 3x10 11 joule.

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. –Baryon (3 quarks) Electrons carry a fundamental negative charge. –Leptons Neutrons carry no net charge. Proton Quarks +1 (+⅔ +⅔ -⅓) u u d Electron Lepton 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?Charge 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 10 18 elementary charges.

Fundamentals of Electricity The proton has a positive elementary charge. The electron has a negative elementary charge. The neutron has a net charge of zero. Proton+ 1.6 x 10 -19 C Electron- 1.6 x 10 -19 C Neutron0

Q = ne Q is the charge of object (in coulombs) n is the number of elementary charges e is the elementary charge

Q = ne How many excess electrons are on an object with a charge of - 8.0 x 10 -19 C

Transfer of Electric Charge Materials with a mobile sea of free electrons, are called conductors. –Metals, 10 28 /m 3 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 0 - 5pC + 5pC 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. -7pC + 4 pC - 18pC + 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. Electrons are forced from the left side of the sphere to the right side, charge separation A Ground connection is made. And the electrons “escape” to ground, neutralizing the right side of the sphere. The charged rod is removed and the net positive charge is re- distributed

Charging by Induction A neutral conducting plate is brought near a negatively charged insulator plate. Electrons are forced from the bottom of the conductor to the top side. charge separation A Ground connection is made. And the electrons “escape” to ground, neutralizing the top side of the plate. The plate is removed and the net positive charge is re- distributed

Using two metal spheres and a charged object, how could you charge one sphere positive and one negative? AnswerAnswer

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 Force of repulsion is equal in magnitude on both charges regardless of the charge. q1q1 q2q2

Coulomb’s Law F = kq 1 q 2 /r 2 Electrostatic constant k = 8.99 x 10 9 Nm 2 /C 2 Click on Link Above for Example. r Force of repulsion is equal in magnitude on both charges regardless of the charge. q1q1 q2q2

The Electric Field + + The Electric Force per unit charge, where the test charge is a positive point charge. TEST CHARGE E = F/q Electric Field is a vector quantity

The Electric Field + + The Electric Field around a point charge obeys an INVERSE SQUARE LAW INVERSE SQUARE LAW Field lines point away from positive charges E = kq/r 2 E = F/q

Electric Field Electric Field Rules + test charge + Line Density shows relative field strength Field lines never cross Start and end on surface of a conductor at 90 o Directed away from positive

Electric Potential + Electric potential lines form right angles with Electric lines of force. Equipotential lines Electric potential is the Energy per unit charge. V = W/q Electric Field lines Electric Potential is a Scalar quantity

Electric Potential + Equipotential lines around a point charge form right angles with Electric lines of force. Equipotential lines V = W/q Electric Field lines Electric Potential is a Scalar quantity

Electric Potential Energy W = F d, U = kq 1 q 2 /r r The potential energy stored in the system of both charges regardless of the charge. q1q1 q2q2

Electric Potential Energy W = F d, U = kq 1 q 2 /r r The potential energy stored in the system of both charges regardless of the charge. q1q1 q2q2

Electric Field Formulas F = kq 1 q 2 /r 2 E = kq/r 2 E = F/q U = kq 1 q 2 /r V = kq/r V = W/q E = V/d VectorsScalars

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.lightning

Millikan's Oil Drop Experiment Click Link Showed the existence of an elementary charge

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