1. Electrostatics

2. Charges Electrons Negative q = -1.6 x 10 -19 C Protons Positive q = +1.6 x 10 -19 C Neutrons Neutral

3. Materials Conductors: Materials in which electrons can move freely (have more freedom to roam than in other materials) which allows charge to move through the material easily Also good conductors of heat Most metals are good conductors Insulators: Materials in which electrons are tightly bound and have little to no freedom to move which causes charge to not flow easily Also NOT good conductors of heat Examples: rubber, glass, plastic, foam

4. Semiconductors: Materials that fall between conductors and insulators In pure state, act as insulators If introduce impurity, can increase ability to conduct significantly Examples: germanium, silicon  used in electronic devices, layered to form transistors Superconductors: At certain temperatures are perfect conductors which allow the electrons to flow indefinitely For some metals this occurs at absolute zero (0K or -273 o C) Examples: tin, aluminum, metallic alloys

5. Charged Objects How does an object become charged? Valence Electrons Charging Methods Friction Contact Induction Polarization http://phet.colorado.edu/en/simulation/travoltage http://phet.colorado.edu/en/simulation/balloons http://phet.colorado.edu/en/simulation/electric-hockey

6. Charging by friction: Electrons are transferred by friction when one material rubs against another Examples: stroke cat’s fur and hear crackle of sparks Comb your hair on dry day and hear/see sparks of electricity Feel shock when touch doorknob Fleece blankets Playground slides Charging by contact: Electrons are directly transferred from one object to another through touching one object to the second A charged rod contacts a neutral object If neutral object is a good conductor, the extra charge will spread out throughout the surface of the object since like charges repel each other If neutral object is a poor conductor, may have to touch the rod in several places on the object in order to get a more uniform distribution of charge

7. Charging by induction: Electrons move and charge is produced, but no contact occurs Inducing a charge in two conducting spheres: “grounding” something allows the object to have a conducting path to an infinite reservoir for electric charge – the Earth This is why lightning rods are on buildings Lightning occurs because there is an electrical discharge between oppositely charged parts of the clouds Negatively charged bottom of the clouds induce a positive charge on the ground/surface of the earth

8. Charging by polarization: Similar to charging by induction in conductors, but polarization occurs only in an insulator where the electrons are not as free to move Instead of free electrons moving, the molecules within the object rearrange so that all positive ends are pointing one direction and negative ends are pointing opposite direction Once object is polarized, still has no net charge (is neutral), but can attract/repel objects due to the realignment of charge within the object Ex. Charged comb picks up pieces of paper, charged balloon by stream of water can attract water

9. Coulomb’s Law Use magnitude of charges in equation. Like charges give a repulsive force and unlike charges give a force of attraction

10. Charges in Equilibrium Occurs where the net electric force on a charge is zero Have to find the position where a third charge can be placed so that the electric force from charge 1 is equal and opposite to the electric force from charge 2