Electric Charge and Force Chapter 17.1 Notes

Electric Charge Electric charge is an electrical property of matter An object can have a negative charge, a positive charge, or no charge at all Positive and negative electric charges are opposite—an object with equal amount of positive and negative charge has no net charge Energy is never created nor destroyed Conservation of charge is a fundamental law of nature

Opposites Attract Like charges will repel one another Positive and positive will repel; negative and negative will repel Opposite charges are attracted to one another Electric charge depends on an imbalance of protons and electrons Remember that atoms are made of protons, electrons, and neutrons Protons have a positive charge, electrons have a negative charge, and neutrons have no charge Negatively charged objects have more electrons than protons; positively charged objects have fewer electrons than protons The SI unit of electric charge is the coulomb (C)

Transfer of Electric Charge Protons and neutrons are relatively fixed in the nucleus of the atom, but the outermost electrons can easily move from one atom to another When different materials are rubbed together, electrons can be transferred from one material to the other The direction in which the electrons are transferred depend on the materials

Conductors and Insulators Materials, such as copper, are called electrical conductors Conductors allow electric charges to move freely Materials that do not transfer charge easily are called electrical insulators Cardboard, glass, silk, and plastic are insulators The charges in a neutral conductor can be redistributed without actually changing the overall charge of the object When doing so, the total charge on the object is still zero, but the opposite sides will have an induced charge

Charging by Contact The transfer of electrons from one object to another can charge objects When a negatively charged object touches a neutral object, some electrons move from the negative object to the neutral object Both objects will then have a negative charge

Charging by Friction and Induction Sometimes objects can gain a charge by rubbing against one another through friction For example, if you slide across the seat of a car, one material will gain electrons becoming negatively charged The other material will lose electrons becoming positively charged When a charged object is brought near a neutral insulator, it causes the positions of the electrons within the insulator to change slightly—one side will have an induced positive charge and one side will have an induced negative charge

Electric Force The electric force is the force of attraction or repulsion on a charged particle that is due to an electric field The electric force at the atomic and molecular levels is responsible for most of the everyday forces that we observe, such as the force of a spring and the force of friction The electric force is also responsible for holding atoms together The greater the amount of charge on two objects, the greater the electric force The greater the distance between two objects, the lesser the electric force

Electric Field An electric field is the space around a charged object in which another charged object experiences an electric force One way to show an electric field is by drawing electric field lines Electric field lines point in the direction of the electric force on a positive charge

Electric Field Lines Electric field lines never cross one another Field lines can show both the direction of an electric field and the relative strength of each charge