# Electrical Charges and the Electrical Interaction What do you know about electrical charges and their behavior? What do you know about electrical charges.

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Electrical Charges and the Electrical Interaction What do you know about electrical charges and their behavior? What do you know about electrical charges at the molecular, atomic, and subatomic level?

Electrical Charges and the Electrical Interaction Charges in nature nucleon level and larger sub-nucleon level questions raised by electrical understanding of atoms

What are charged particles?

Electrical Charges and the Electrical Interaction Charges as the bearers of the electrical interaction one kind of charge, but positive and negative Like charges repel each other and opposite charges attract each other.

Scotch tape lab X-rays from Scotch tape http://www.exo.net/~pauld/summer_institute/summer_day14electrostatic/ta pe_electroscope.html Four pieces of tape Pull two pieces off of table – bring near each other Pull two pieces off of other tape – bring near each other Pull one piece off of table, another off of a piece of tape, bring near each other Demonstrate likes repel, opposites attract?

Gravitational Force Electrical Force (Coulombs Law) Do assignment 5 worksheet on Coulomb’s law

Van de Graff demo The dielectric breakdown strength of dry air, at Standard Temperature and Pressure (STP), between spherical electrodes is approximately 33 kV/cmdielectric breakdownStandard Temperature and Pressure

The Ability of Materials to Transport Charge Insulators and conductors great range of conductivity Superconductors Semiconductors Iron man

Processes of Charging By friction By contact By induction

Processes of Charging By friction By contact By induction http://phet.colorado.edu/en/simulation/travoltage

Processes of Charging By friction By contact By induction

Electroscope lab

Processes of Charging By friction By contact By induction If the metal sphere is grounded while the wand induces a charge, the electrons will flow away to ground and leave the sphere with a net positive charge.

Electric Field

The Electric Field The concept of a field compared to action at a distance Representation of the electric field by lines of force http://web.ncf.ca/ch865/englishdescr/3DEFldIdentCharges.html http://phet.colorado.edu/en/simulation/electric-hockey What would the electric field lines look like for a charged conducting sphere? What would the electric field lines look like for a charged conducting plate?

Electric Potential Definition distinction from electric potential energy analogy to gravitational potential

E is force per unit charge V is Electric potential energy per unit charge E is force per unit charge V is Electric potential energy per unit charge

Parallel plate capacitor

Charge separation An atom can become electrically polarized if a nearby charge causes its electron cloud to become distorted. Charge separation in atoms can be a widescale effect.

Conceptual questions 1) Why do clothes often cling together after tumbling in a clothes dryer? 2) At some automobile toll-collecting stations, a thin metal wire sticks up from the road and makes contact with cars before they reach the toll collector. What is the purpose of this wire? 3) An electroscope is a simple device consisting of a metal ball that is attached by a conductor to two thin leaves of metal foil protected from air disturbances in a jar, as shown. When the ball is touched by a charged body, the leaves that normally hang straight down spread apart. Why? (Electroscopes are useful not only as charge detectors, but also for measuring the quantity of charge: the more charge transferred to the ball, the more the leaves diverge.) 4) Is it necessary for a charged body to actually touch the ball of the electroscope for the leaves to diverge?

Conceptual questions 5) The five thousand billion, billion freely moving electrons in a penny repel one another. Why don't they fly out of the penny? 6) How does the magnitude of electric force compare between a pair of charged particles when they are brought to half their original distance of separation? To one-quarter their original distance? To four times their original distance? (What law guides your answers?) 7) The proportionality constant k in Coulomb's Law is huge in ordinary units, whereas the proportionality constant G in Newton's law of gravitation is tiny. What does this indicate about the relative strengths of these two forces? 8) If you rub an inflated balloon against your hair and place it against a door, by what mechanism does it stick? Explain.

Conceptual questions 9) How can a charged atom (an ion) attract a neutral atom? 10) If you place a free electron and a free proton in the same electric field, how will the forces acting on them compare? Their accelerations? Their directions of travel? 11) Suppose that a metal file cabinet is charged. How will the charge concentration at the corners of the cabinet compare with the charge concentration on the flat parts of the cabinet?

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