Electrostatics: Electricity at Rest Chapter 16 Electrostatics: Electricity at Rest

Facts About the Atom Protons Neutrons Electrons positive charge, don’t move Neutrons no charge, don’t move Electrons negative charge, move

Facts About the Atom Atoms normally have equal p+ and e- and are therefore neutral To have a charge they must gain or lose the electrons

Electrical Charges Fundamental Rule: Like charges repel Opposite Charges Attract

Conservation of Charge Total amt. of charge remains the same but may be rearranged. Ex: a rubber rod is rubbed with fur, electrons are transferred from the fur to the rod Ex: a plastic rod is rubbed with silk, electrons are transferred from the rod to the silk

Conductors vs. Insulators Conductor – electrons can move easily Metals electron sea Insulator - Tightly bound electrons Rubber Glass

Creating charge by Induction Bring charged item near neutral conductor and it will polarize its charge

Forces Newton’s Law of Universal Gravitation F = G m1m2 d2 Attractive Depends on mass G = small magnitude = weak force

Forces Coulomb’s Law F = k q1q2 d2 Attractive or Repulsive Depends on Charge k = large magnitude = strong force

Coulomb’s Law F = k q1q2 d2 k = 9.0 x 109 N•m2/C2 Unit of Charge - Coulomb (C)

Coulomb’s Law Sirap rubs two latex balloons against her hair, causing the Balloons to become charged negatively with 2.0 x 10-6 C. She holds them a distance of 0.70 m apart. What is the electric force between the two balloons?

Coulomb’s Law When sugar is poured from the box into the sugar bowl, the rubbing of sugar grains create a static electric charge. If two sugar grains each acquire a charge of 3.0 x 10-11 C at a separation of 0.00080 m, with what force will they repel?

Coulomb’s Law Two balloons acquire a charge of 2.0 x 10-7 C each. How large is the electric force between them when they are separated by a distance of 0.50 m?

Coulomb’s Law A raindrop acquires a negative charge of 3.0 x 10-18 C as it falls. What is the force of attraction when the raindrop is 6.0 cm from the end of a car antenna that holds a charge of 2.0 x 10-6 C?

Coulomb’s Law In a grain elevator, pieces of grain become electrically charged while falling through the elevator. If one piece of grain is charged with 5.0 x 10-16 C while another holds a charge 2.0 x 10-16 C. What is the force between them if they are separated by 0.050 m?

Lightning!! Clouds build up static electricity Ground is inductively charged Discharge!!! Lightning rods – slowly drain charge Use Ellen’s Video – start at 7 minutes to discuss how clouds get charged 2 reasons for lightning rods