Chapter 32: Electrostatics Conceptual Physics Bloom High School

32.1 Electrical Forces and Charges Electrostatics- electricity “at rest” Electrical forces- like gravity, can attract Unlike gravity, can also repel Charge- electrons (-), protons (+) 1. Every atom has a (+) nucleus surrounded by (-) 2. All (-) are identical in mass and charge 3. All (+) are identical in mass and charge. The nucleus also contains neutrons, which are neutral. A proton is equal in mass to a neutron, but 2000x more massive than (-) 4. Neutral Atoms have an equal number of (-) and (+)

Like attracts like (only in chem) Like charges repel, opposite charges attract

32.2 Conservation of Charge Conservation of Charge- electrons may not be created nor destroyed! Protons cannot be gained or lost from an atom Electrons are only gained or lost in whole number quantities There’s no such thing as losing 1.5 electrons! Anion- an atom that has gained one or more (-) Negative ion Cation- an atom that has lost one or more (-) Positive ion

32.3 Coulomb’s Law Universal Gravitation (Ch 12) Coulomb’s Law (Ch 32) Fg=G(m1m2)/r2 G=6.67x10-11 Nm2/kg2 m=mass of an object (kg) r=distance between objects (m) F=gravitational force between particles (N) Coulomb’s Law (Ch 32) Fe=k(q1q2)/r2 k=9x109 Nm2/C2 q=charge on a particle (C) r=distance between particles (m) F=electrostatic force between particles (N)

Coulomb’s Law Force is inversely proportional to distance Larger r=weaker F q can be positive or negative Allows for an attractive force is q’s are opposite (+q)(+q)  +F and like charges repel! (-q)(-q)  +F and like charges repel!

Comparison of Fg and Fe For a Hydrogen atom: Fe=k(q1q2)/r2 qe=-1.6x10-19 C qp=1.6x10-19 C r=5.3x10-11 m Fe/Fg=2.2x1039 stronger!!! Fe=8.2x10-8 N Fg=G(m1m2)/r2 me=9.1x10-27 kg mp=1.7x10-31 kg Fg=3.7x10-47 N

32.4 Conductors & Insulators 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 Insulators- outer electrons are fixed No energy can be transmitted Ceramics, rubber, dry wood, pure water

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

32.5 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

32.6 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

32.7 Charge Polarization Electrically Polarized- when one side of a molecule has a larger electron cloud than the other By design or by induction

Summary of Causes of Charges 1. By friction, through rubbing objects together 2. By contact, through touching of a charged object to another conductive object 3. By induction, bringing a charged object near another object, but not necessarily with touching