Monday, April 29 Reminders: Sound and Light Test Make-Up TODAY after school or during Lunch Schedule time with Mr. Kipp Today In Class: Continue discussion of Electrostatics

Electrostatics - recap from Friday Electrostatics is electricity at rest; electricity in its natural state (without being forced through wires, etc.); and the concept of charge. "Like repels like"; "opposites" attract Examples: protons (positive) attract electrons (negative) but electrons repel other electrons

2 negatively charged particles repel each other.

How are objects normally charged? What charge do they naturally have? Most objects and materials are naturally in a state of neutral charge (or no charge) because they naturally have a more-or-less balanced number of electrons and protons. An object that has unequal numbers of electrons and protons is considered to be electrically charged (either positively or negatively).

Conservation of Charge Electrons are neither created nor destroyed, they just transfer from one material to the other. Therefore, an object can be given a charge by simply adding to or removing a number of electrons. But, these electrons have to come from another source.

Coulomb's Law - how we calculate charge The SI unit of charge is the coulomb, abbreviated C. Much like Newton's law of gravitation, Coulomb's Law states that the closer two like- charged materials are to each other, the greater the repulsive force, and vice versa. Because most objects have almost exactly equal numbers of electrons and protons, electrical forces usually cancel out. Therefore, they don't normally have any force of attraction or repulsion.

Conductors and Insulators Electrons move easily in good conductors and poorly in good insulators. Metals have "loose" outer electrons, therefore they are good conductors. Insulators have tightly bound electrons that remain with their particular atoms (examples: rubber, glass). Therefore, the electrons don't transfer, hence no charge. Semi-conductors can be made to either be good insulators or conductors.

Charging by Friction and Contact Electric charge can be transferred by friction and by contact; either rubbed together or simply by touching Charging by Induction - (no contact) If a charged object is brought near a conducting surface, even without physical contact, electrons will move in the conducting surface, (ie, lightning). Grounding - charges are moved off of a conductor by touching it.

Today's assignment Complete and submit Chapter 32 Electrostatics questions to the basket before you leave. You should have plenty of time to complete the assignment. When done, quietly use the remaining class time wisely.