Chapter 26 Electrostatic Forces Coulombs Law Electric force

Chapter 26 Electrostatic Forces & Coulomb’s Law

• Electric force is a fundamental force of nature… • Lightening is uncontrolled, but electricity is controlled

Through the discovery of the electron, these conclusions are assumed… Charged objects exert forces on each other Any charged object will “pick up” small pieces of paper. Charges are transferred through touch. Two major types of materials, conductors and insulators.

• Insulators have electrons tightly bound to their nuclei which prohibits current to flow. (rubber, wood, glass…. ) • Conductors have electrons weakly bound to their nuclei which promotes current to flow. (copper, silver, platinum…)

Charge Model… 1. 2. 3. 4. 5. Friction causes charging 2 types of charge exist Like charges repel while opposite attract Strength of a charge field depends on distance Neutral objects have same number of positives and negatives 6. 2 types of materials exists 7. Charges transfer through contact

Chemistry Review….

• Electrons and protons are basic charges of matter. Their motion is governed by Newton’s Laws. Electrons can move from one object to another when contact is made, but neither particles can leap through the air from object to object.

Homework… • #2, 5, 6 and 11 page 813

• Charge is represented by Q or q. q= Npe – Nee protons and electrons have equal charge, but opposite sign. + or – 1. 6 x 10 -19 C

• Because electrons are in the outer most position in an atom, they are easily lost during the ionization process.

Rank in order from most positive to least positive…

• e>a>d>b>c Cam’s red number line was right…I was wrong!!!

• Insulators can be charged by rubbing where as conductors cannot. • Static equilibrium occurs when charges are isolated and at rest with no net force. • In an isolated conductor (brass door knob) the charge is located on the surface.

• People and earth are both good conductors due to the fact they are large salt water. • The purpose of “grounding” an object to earth is to move excess electrons to a huge surface and disperse them.

How does an object become polarized?

• When we polarize an atom, the shape of the atom becomes more “pill” shaped than the standard sphere we normally imagine. • As you move a charged “rod” near a conductor or insulator, the atoms inside act completely different. In the conductors all of the particles actually move while in an insulator, the atoms simple realign without motion.

• The electric force increases for objects with more charge and decreases as charged objects are moved further apart, this is known as Coulomb’s Law. F= (k|q 1 q 2|) ÷r 2

F= (k|q 1 q 2|) ÷r 2 According to Coulomb’s Law, forces occur in pairs that are equal in magnitude and opposite in direction. Forces are directed along a line joining the particles and is repulsive for two like charges and attractive for oppositely charges particles.

Homework… • #14, 15, 22, 31 and 32 page 813 -816

• SI unit for charge is C (coulomb) and 1 C is equal to 6. 25 x 1018 protons. • Restrictions of Coulomb’s Law: - only applies to point charges -only applies to electrostatics -electric forces can be superimposed

• A point charge comes form one spot and only affects the space around itself. • A field is a simultaneous force at “all’ points in an area due to the interactions of multiple point sources.

• Electric field is defined as a force to charge ratio and recorded in N/C. • E is a vector field • If q+, electric field vectors point in the same direction as the force…If q-, electric field vectors point in the opposite direction as the force.