1. Electricity Chapter 17

2. Chapter 17- Electric Charge The two different kinds of Electric charges are positive and negative Like charges repel – unlike charges attract Protons and neutrons are relatively fixed in the nucleus of the atom but electrons are easily transferred from one atom to another.

3. Chapter 17- Electric Charge All charge is a result of the movement of electrons. (Chemistry Review) –All atoms begin as neutral- with no charge. –If you take away negative electrons then the atom has a positive charge. –If you add negative electrons then the atom becomes negatively charged. –All atoms with a charge are called ions.

4. Chapter 17- Electric Charge What causes the electrons to move? Friction! When objects rub together electrons are moved from one object to the other. This causes one object to be positively charged and the other to be negatively charged and the process is called charge by contact.

5. Chapter 17- Electric Charge

6. The fundamental unit of charge, e, has been determined to be 1.6 X 10 -19 coulombs C (coulomb) is the SI unit of electric charge 1.0 C contains 6.2 X 10 18 electrons

7. Chapter 17- Electric Charge Materials in which electric charges move freely are called conductors. –Ex: Copper, Aluminum, most metals Materials in which electric charges do not move freely are called insulators. –Ex: Wood, glass, styrofoam Semiconductors are materials between conductors and insulators. –Ex: silicon, germanium

8. Chapter 17- Electric Charge Grounding is when a conductor is connected to the Earth by another conducting object such as copper wire. Many times it is a safety precaution in electrical devices. Induction is the process of charging a conductor by bringing it near another charged object and grounding the conductor.

9. Chapter 17- Electric Force Electric Force – two or more charged objects near one another may experience motion either toward or away from each other because each object exerts a force on the other objects. Electric force is an example of a field force

10. Chapter 17- Electric Force Coulomb’s Law F electric = k C (q 1 q 2 /r 2 ) Electric force = Coulomb constant X (charge 1)(charge 2) / (distance) 2 Coulomb constant in SI units: k C = 8.99 X 10 9 Nm 2 /C 2

11. Chapter 17- Electric Field Electric field – a region in space around a charged object in which a stationary charged object experiences an electric force because of its charge. No contact needs to take place for this to occur

12. Chapter 17- Electric Field Electric field strength is a ratio of force to charge; the SI unit is N/C (Newton/Coulomb) It also depends on charge and distance E = k C (q/r 2 ) Electric field strength = Coulomb constant X charge producing the field/(distance) 2