Chapter 15 Electricity and Magnetism

History of Electrostatics Electrostatics is the study of the nature, behavior, and uses of static electricity. Benjamin Franklin is famous for his study of electricity!

The Study of Static Electricity The Electric Charge: We know that all matter consists of tiny particles called atoms which contain protons, neutrons, and electrons. Protons and electrons have a certain amount of “electric charge.” This electric charge enables them to attract and repel each other.

The Study of Static Electricity The Electric Charge cont… Protons are positive (+) Electrons are negative (-) Electricity is the result of the transfer of electrons.

The Study of Static Electricity Ordinarily – the charges are in equal balance and the atom is said to be “neutral.” If an atom loses and electron or gains an electron, it is “charged”.. To many electrons? It is negatively charged. To many protons? It is positively charged.

The Study of Static Electricity Opposite charges neutralize each other!!! One of the ways to cause an atom to gain or lose electrons is with friction. When an objects “rub” against each other, the electrons can “rub off” one object onto another.

The Study of Static Electricity Whenever charges are built up in two objects by friction, one object is charged negatively and the other is charged positively.

Electric Fields We cannot see electric fields – we CAN map them with imaginary lines. These lines are called “lines of Force”

Measuring Charge The more electrons an object gains or loses, the stronger its charge will be. The unit of charge is the “coulomb” One coulomb equals 6.24 billion billion electrons. (6.24 X )

Electrostatic Laws Law of electric charges: opposite charges attract each other, like charges repel each other Law of electric force: strong charges attract strongly, weak charges atatract weakly

Electrostatic Laws Coulomb’s Law of Electric Force - strength of the attraction or repulsion is directly related to the strength of the charges and inversely related to the distance between them.

Coulomb’s Law of Electric Force The force between two charges is 100 Newtons 1. What happens if the distance d is doubled? 2. Double both charges? 3. Double d and charges?

Sharing a Charge Contact – neutral object touches a charges object – charged object transfers the charges. This can happen with positive and negatively charged objects. Charging by contact is permanent! The transfer of charges is conserved – that is the amount of charge is the same before and after the transfer.

Transferring Charges An object’s charge can be taken away completely by bringing it into contact with the ground! The earth is so “huge” it can soak up an object’s electrical charge. This is called grounding!

Inducing a Charge A temporary transfer happens without direct contact. This is called “induction” Charging by induction produces two “new” charges instead of one. The example of this is the balloon on your hair!

Detecting Charges Small charges can be detected by means of an electroscope. When uncharged, the foil leaves stay down. When charged, the foil leaves rise up.

Electrostatic Generators The Van de Graaff Generator The charges move outward!

Protection from Lightning Benjamin Franklin knew that if the charge from a lightning strike could be directed into the ground, then the strike would be harmless. So, He invented the Lightning Rod.

Protection from Lightning Franklin’s famous experiment is VERY DANGEROUS! Numerous people over the years have tried to duplicate it and have died from being struck by lighting! Do not attempt!

Magnets and Magnetism The first magnet ever used was actually a lodestone which is a natural magnet. It is a form of the mineral magnetite!

Magnets and Magnetism The Vikings were the first to use lodestones for navigation.

The Nature of Magnets Magnets come in various sizes and strengths. Magnets are used in televisions and speakers and computers.

Magnetic Fields The property of attracting objects by the magnetic force is known as magnetism. The region around a magnet that other objects are attracted to are the magnetic field. Compasses are affected by these fields. The iron filings represent lines of force.

Law of Magnetic Poles All magnets possess poles. One pole always seeks North. One pole always seeks South. The Law of Magnetic Poles states: Like poles repel and unlike poles repel.

Law of Magnetic Poles ical_science/magnetism/bar_magnet_inter active.html