Types of Electric Charge

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Ch.9.1 – Types of Electric Charge

* Static electricity : static cling of clothes out of dryer; lightning; * Walk across carpet and touch get a shock touching metal doorknob – friction of shoes against carpet cause you acquire static electric charge * Static charge – electric charge at rest, stays on and eventually discharged or lost to other objects/air * Discharge – remove excess static charge so the object is neutral * Static charge last long when air is dry

* Electrostatics – study of static electric charge

* Benjamin Franklin demonstrated lightning is a form of electricity by flying a kite during a thunderstorm * Kite made out of silk and had pointed wire tip 30cm to draw “electric fire” * Flew kite using piece of twine tied to ground & metal key tied to twine by silk *

* 2 types of charge: positive & negative
* Object with no net charge is neutral (equal amounts of positive & negative) * Law of Electric Charges – like charges repel and unlike charges attract * Benjamin Franklin imagined an electric charge was a type of fluid and believed every object contained “natural amount” of the fluid * When rubbed against another, one lost some fluid and one gained some * Positive indicate an object had more than the natural amount * Charges could easily been called red and green; positive & negative makes adding up the total charge easier

Atomic Structure and Electric Charge
* Atoms made up of smaller particles
* Protons – positive charge, large mass (2000x larger than electron) * Electrons – negative charge, tiny mass
* Neutrons – no charge, similar mass as proton
* Protons and neutrons in nucleus of atom and do not move when atom becomes charged * Electrons move around outside of nucleus and can be easily added/removed from an atom * Atom with same number of protons and electrons is neutral; unequal number has an electric charge * Ion – atom that has an electron charge

* Negative ion picked up extra electrons; positive lost electrons * Neutrons does not make atom neutral

Positive, Negative, and Neutral Objects
* Only electrons can move, protons remain in the nucleus of an atom * Electrons can be transferred from one object to another, one lose electrons and other gains electrons, both objects become charged The Electrostatic Series

* Some materials are more likely to gain/lose electrons than others * 1 object gains electrons from another object that loses electrons

Attraction of Neutral Objects to Charged Objects
* Neutral objects are not attracted/repelled from each other * Induced charge separation – slight shift in the position of electrons

Ch.9.2 – Charging by Friction, Conduction, and Induction
* Charging by friction – 2 objects rubbed together, causes electric charges to be transferred from one object to another * Hair and comb are both neutral; when, rubbed together, polyethylene atoms have stronger attraction for electrons than hair atom * Rubbing transfers electrons; hair becomes positively charged and comb becomes negative * Charging by conduction – when objects touch and an electric charge is transferred from one to another * When a negatively charged bar contracts a neutral sphere, some of the extra electrons move to the sphere giving it a negative charge * Charging by induction – when objects are charged without touching or making any direct contact * When a negatively charged bar comes near a neutral sphere, the charge on the bar causes, or induces, the electrons on the sphere to change their position

Ch.9.3 – Insulators and Conductors
* Insulator – substance in which the electrons are so tightly bound to the atom making up the material that they are not free to move to a neighboring atom. (plastic) * Conductor – allows electrons to flow freely from one atom to another. (metal, copper) * Semiconductors – allow...
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