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Home , Static electricity

(aka “Static ”) What is Electrostatics?

• Electrostatics is the study of the behavior of stationary charged objects. It’s all about the (in constant, random motion around the nucleus) and (stuck in the nucleus)

Negative

Nucleus: positive protons & neutral neutrons The Atom & its particles… • Electrons are negatively charged particles moving around the nucleus (in orbitals) • electron = e- • Protons are positively charged particles located inside the nucleus (w/the neutral neutrons) • = p+ • Electrons are able to be stripped off an atom (friction: fur & pvc pipe) • Protons are NOT able to leave an atom because they’re stuck in the nucleus!

Types of Materials 1. Conductor: a material that transfers charge easily (ex. Metals: gold, silver, copper). 2. : a material that does not transfer charge easily (ex. Plastics, glass, cork) 3. Semiconductors: somewhere between 1 & 2 (ex. Silicon, carbon, germanium). 4. Superconductors: some metals become perfect conductors below certain temperatures 5. Train Conductor: a person who drives a train.  Law of Conservation of Electrical Charge • Electrons may be transferred from one object to another, but they will never disappear or appear from nowhere. • Electron abundant = negative charge • Electron deficient = positive charge Electrically charged objects... • Exert a force on each other • Unlike charges attract • Like charges repel There are four methods to charge an object: 1. Charging by Friction • using friction to remove electrons from one object and placing them on the other object. Result: two objects with opposite charge • Walk across carpeted floor with wool socks and you can build up an excess of charge (either on you or the carpet) and therefore, become charged. • Fur becomes positively charged. Why? • Rod becomes negatively charged. Why? • Can use friction to remove electrons from fur and deposit onto rod. 2. Charging by Contact (or Conduction)

• The process of giving one object a net by placing it in contact w/another object that is already charged is known as charging by contact. • Result: two objects with same charge

3. Temporarily Charging by Induction

• An object may become polarized (opposite ends) while a charged object is brought near. But, the overall charge on this piece of plastic (for example) is neutral. • Result: two objects with opposite charge temporarily • When the charged rod goes away, the electrons rearrange and disperse evenly. Object is still neutral. 4. Permanently Charging by Induction • The process of giving one object a net electric charge without touching the object to a second charged object is called charging by induction. Permanently Charging Polarization by Induction 5. Credit Card Charging:

• You may use Visa, Master Card, or American Express • Result: Debt from high interest rates!

Check out these animations!

• http://phet.colorado.edu/simulations/sims.p hp?sim=John_Travoltage • http://phet.colorado.edu/simulations/sims.p hp?sim=Balloons_and_Static_Electricity Van de Graaf Generator

Electric Fields • What is an ? • A region of space where a charge exerts a force on other charged objects. This field extends outward and permeates all of space. • Direction of Electric Field = Direction of Force the field produces on a positive charge in the field. • In comparison: What is a gravitational field? • How to measure an electric field: Using a SMALL POSITIVE test charge, move it around a charged object (that is creating an Electric Field) and the magnitude and direction of force acting on the small positive test charge is measured. • The strength of the field is measured based on the force on the test charge. F ..on..q F E  E  q q • F = The force felt by (acting on) the test charge, q, due to the point charge’s electric field. (N) • q = the charge of the test charge. (C) • E = Electric Field Strength. (N/C) (Direction is based on imagining a small positive charge in the field.) • The Electric Field (E) at a given spot can exert a variety of forces, depending on the magnitude of the test charge placed there.

• E = F/q = F/q = F/q • E is constant for that particular point charge at a given location (the Point Charge is the charge whose field is being tested… the point charge is creating the Electric Field. ) Compare

• Compare the electric field equation to the one we used to measure Earth’s gravitational field strength: F F a  E  m q

• So, Electric Fields are measured in N/C and are a measure of the force felt by a small positive test charge. (The test charge must be small in charge so that we can ignore its electric field.) Electric fields: Man holding point charge, girl holding test charge.

Must click on 2nd link!

• http://phet.colorado.edu/simulations/sims.p hp?sim=Electric_Field_Hockey http://phet.colorado.edu/simulations/sims.ph p?sim=Charges_and_Fields http://phet.colorado.edu/simulations/sims.ph p?sim=Electric_Field_of_Dreams