Chapter 20 Notes Static Electricity
Ben Franklin’s experiment in 1752 • Electrostatics-The study of electrical charges that can be collected and held in one place, in other words, they are AT REST
Something about ATOMS • Every atom has a positively charged nucleus surrounded by negatively charged electrons • All electrons are identical (same mass and charge) • Nucleus=protons and neutrons • Atoms usually have an equal number of protons and electrons
Charge • Electrons are negatively charged • Protons are positively charged • The attracting and repelling is due to something called charge • LIKE CHARGES REPEL • OPPOSITE CHARGES ATTRACT
Insulators • Materials through which charges will not move easily • Examples-glass, dry wood, plastics, cloth, dry air
Conductors • Materials, such as metals, that allow charges to move about easily. Charge spreads very quickly over the entire object • Examples-door knob, desk, lightening rod
Why are metals good conductors? • Because at least one electron on each atom of the metal can be removed easily; they move freely throughout the entire piece of metal • Most of the time, the materials involved in Static Electricity are nonconductors of electricity
Conservation of Charge • Individual charges are never created nor destroyed • The combined total charge of 2 interacting objects remains the same
Things to Remember!! • 2 Kinds of Electrical Charges-Positive & Negative • Charges exert force on other charges over a distance • The force is stronger when the charges are closer together • Like charges repel, Opposite charges attract
How do we Charge Object? • Conduction Charging a neutral object by touching it with a charged object
Induction Charging a neutral object by bringing it close to a charged object, causing a separation of charges, then removing the object to be charged, trapping equal but opposite charges
Coulomb’s Law • Says that the magnitude of a force between 2 charges varies directly with the magnitude of the charges and inversely with the square of the distance of the charges • F=K(qq/d2) • K is a constant • K=9.0x109 Nm2/coul2
Electric Potential Energy • Bodies with diff. concentrations of electrons have a difference in potential between them. • This means that the 2 bodies are a source of potential energy. • The difference in potential is measured in Volts (v)
Electrons flow from areas of higher conc. to areas of lower conc. • An electron flow takes place if 2 bodies have a difference in potential and are connected by a conductor. • This flow is called an electric current.
The way to maintain a current is to maintain a charge on the 2 bodies that are at diff. potentials. • To maintain the potential, some devices must pump the electrons back to the body with higher concentrations as soon as they get to the lower concentration. These are called Voltaic Cells-Batteries.