- Slides: 32
What is Electricity? • Electricity refers to the flowing motion of electric charge. • Electricity refers to the amount of imbalance between quantities of electrons and protons.
• Everything is made of atoms which contain POSITIVE particles called PROTONS and NEGATIVE particles called ELECTRONS. Electron m=9. 11 x 10 -31 KG Proton m=1. 673 x 10 -27 KG Neutron m=1. 675 x 10 -27 KG
• An atom will usually have the same number of positives and negatives • This makes the atom NEUTRAL. Q=Ne Where: Q is the electric charge N is the number of electrons(added or removed) e= 1. 6 x 10 -19 C Coulumb
e. g #1: What is the value of charge on a body which carries 20 excess electrons? N=20 e= -1. 6 x 10 -19 C As q=Ne q= 20 * -1. 6 x 10 -19 C q= - 3. 2 x 10 -18 C
Law of Conservation of It is possible to Electric Charge transfer electric charge During any process, from one object to the net electric charge of an another. isolated system remains constant(is conserved) The body that loses electrons has an excess Charges arecharge, equally while of positive sharedwhen objects the body, that gains of different charges come electrons has an excess into contact w/ each of negative charge other
• Like charges repel and unlike charges attract each other.
• Not only can electric charge exist on an object, but it can also move through an object. • Conductors are materials that permit electrons to flow freely from atom to atom and molecule to molecule.
• Insulators are materials that impede the free flow of electrons from atom to atom and molecule to molecule. e. g. #2: When an oil tanker car has arrived at its destination, it prepares to empty its fuel into a reservoir or tank. Part of the preparation involves connecting the body of the tanker car with a metal wire to the ground. Suggest a reason for why is this done.
History of Electricity • Early cave people probably recognized the force of electricity when lightning struck. They might also have noticed the way amber attracts light objects, or the way certain fishes, such as the electric eel, stun their prey.
History of Electricity • Around 500 B. C. a Greek philosopher named Thales first discovered electricity when he learned that when amber is rubbed with cloth, small bits of straw are attracted.
History of Electricity • Around 1600, William Gilbert, a physician who lived in London at the time of Queen Elizabeth I and Shakespeare, studied magnetic phenomena and demonstrated that the Earth itself was a huge magnet, by means of his "terrella" experiment. He also studied the attraction produced when materials were rubbed, and named it the "electric" attraction. From that came the word "electricity" and all others derived from it.
History of Electricity • In 1752, Benjamin Franklin started experiments with electricity. While trying to prove lightning was electricity he flew a kite in a lightning storm with a key at the end and the lightning touched the key which made a spark.
From this, he made a metal rod to go on a roof so the houses would have no damage.
History of Electricity • In 1786, Luigi Galvani discovered that a dead frog's muscles twitched when it was placed near an electrical machine. He conducted experiments to try to explain why a dead frog appeared to jump. Galvani thought the frog's nerves contained the electricity
History of Electricity • By 1792, Alessandro Volta, disagreed: he realized that the main factors in Galvani's discovery were the two different metals - the steel knife and the tin plate - upon which the frog was lying. Volta showed that when moisture comes between two different metals, electricity is created. This led him to invent the first electric battery, the voltaic pile, which he made from thin sheets of copper and zinc separated by moist pasteboard. The volt is named after Volta.
History of Electricity • Voltage(electromotive force(emf) or potential difference(pd)) – is the electric pressure that causes current to flow voltage = energy charge or V = W(joule) q(coulomb)
History of Electricity • Charles-Augustin de Coulomb, conducted the first quantitative work with electric charges. He studied the magnitude and the direction of the force between two charged spheres in a relation to the magnitude of the charges and distance between them.
• Coulomb’s Law: the force of attraction or repulsion between two small charged bodies is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them. F= k(Q 1 Q 2/d 2) where Q 1 represents the quantity of charge on object 1 (in Coulombs), Q 2 represents the quantity of charge on object 2 (in Coulombs), and d represents the distance of separation between the two objects (in meters). The symbol k is a proportionality constant known as the Coulomb's law constant.
e. G #3: What is the magnitude and direction of the force on a charge of +4 x 10 -9 C that is 5 cm from a charge of +5 x 10 -8 C ? Q 1 = +4 x 10 -9 C Q 2= +5 x 10 -8 C R = 5 cm = 5 x 10 -2 C Find F: F= k(Q 1 Q 2/d 2) = (9 x 109 N C 2)(4 x 10 -9 C )(5 x 10 -8) = 1. 8 x 10 -6 N m 2 / 2. 5 x 10 -3 m 2 F= 7. 2 x 10 -4 N
History of Electricity • Michael Faraday invented the electric motor in 1821. • Georg Ohm, a German, discovered the relationship among voltage, current and resistance in a circuit using direct current. Ohm’s Law deals with the relationship between voltage and current in an ideal conductor. V= I R
History of Electricity • In 1878 Joseph Swan, a British scientist, invented the incandescent filament lamp and within twelve months Edison made a similar discovery in America.
History of Electricity • The recognition of electromagnetism, the unity of electric and magnetic phenomena, is due to Hans Christian Ørsted and André-Marie Ampère in 1819 -1820. • Georg Ohm, a German, discovered the relationship among voltage, current and resistance in a circuit using direct current. The relationship is called Ohm's Law.
Types of Electricity Static Electricity • made by rubbing together two or more objects and making friction • when electrical charges build up on the surface of a material. • when something gives up or gains electrons • objects may be attracted to each other or may even cause a spark to jump from one to the other.
Types of Electricity
Friction - the force between two surfaces rubbing together.
Conduction transfer of electrons from a charged object to another object by direct contact.
Induction the movement of electrons to one part of an object by the electric field of another.
Types of Electricity Current Electricity • the flow of electric charge across an electrical field. • Free electrons continuously move to spaces where electrons are missing. • generated by batteries and power plants.
Types of Electricity
references • http: //library. thinkquest. org/J 001647 F/ • http: //library. thinkquest. org/6064/history. ht ml • http: //www. electricityforum. com/electricityhistory. html