Electrostatics 1 Personal Ad Electron rich…seeks Electron poor for bonding, conducting, and long term relationship. Resistance a plus.

Electrical Forces and Charges 2 The fundamental rule at the base of all electrical phenomena is that like charges repel and opposite charges attract. Electrostatics is electricity at rest.

Electrical forces arise from particles in atoms. In the simple model of the atom, protons in the nucleus attract the electrons and hold them in orbit. 3

Electrons are attracted to protons, but electrons repel other electrons. The fundamental electrical property is which the mutual attractions or repulsions between electrons or protons is assigned to charge. By convention, electrons are negatively charged and protons positively charged. Neutrons have no charge and are neither attracted nor repelled by charged particles. 4

Conservation of Charge An object that has unequal numbers of electrons and protons is electrically charged. An atom with a net positive charge is a positive ion; it has lost one or more electrons. 5

An atom with a net negative charge is a negative ion; it has gained one or more electrons. The principle that electrons are neither created nor destroyed but are simply transferred from one material to another is known as conservation of charge. 6

Coulomb’s Law q = charge of particle; +q or -q Coulomb’s law states that for charged particles or objects that are small compared with the distance between them, 7

the force between the charges varies directly as the product of the charges and inversely as the square of the distance between them. q can be positive or negative Allows for repulsive force is F is positive (+q)(+q)  +F and like charges repel! (-q)(-q)  +F and like charges repel! 8

Conductors Conductors- outer electrons are not well fixed to the nuclei and are free to travel Heat and electricity can be transmitted Most metals, “salt”-based solutions 9

Insulator Insulators- outer electrons are fixed No energy can be transmitted Ceramics, rubber, dry wood, pure water 10

Semi-/Super- conductors Semiconductors- can behave as a conductor or insulator Germanium, silicon Used in circuit boards Superconductors- transmits energy without resistance (heat) Only occurs at temperatures near 0K Limited applications due to low temperature required 11

Triboelectricity Triboelectricity- charging by friction Walking across a carpet and touching a door knob Rubbing a balloon on your head and sticking it on a wall 12

Charging by Induction A charge is drawn away from a pair of touching objects, then the objects are separated Induced- when something is forced to occur Grounding- allowing a charge to flow into the Earth 13

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Charge Polarization Can occur in insulators that are near a charged object Polarization occurs, meaning all the positive charges line up on one side and all the negatives line up on another 15

Ex: rubbing a balloon on your hair gives the balloon a negative charge. When you hold it against the wall, the charges in the wall line up with the positives by the negatively charged balloon, which allows it to momentarily stick 16

Summary of Causes of Charges By friction, through rubbing objects together By contact, through touching of a charged object to another conductive object By induction, bringing a charged object near another object, but not necessarily with touching 17