Electricity

What is electricity? --- All the phenomena caused by positive and negative charges ---

Electric Charges The electric charge is a property of protons and electrons. A proton is positively charged, and an electron is negatively charged.

Electric Charges A negatively charged object has a surplus of electrons (more electrons than protons)

Electric Charges A positively charged object has a deficit of electrons (fewer electrons than protons)

Electrical charges Proton  + charge Electron  - charge A negatively charged body contains more electrons than protons. A positively charged body contains fewer electrons than protons.

Electric Charges elementary charge- charge carried by an electron or a proton. It is 1.602 x 1019 C. Coulomb- unit of measure of the electric charge. A Coulomb is equivalent to the charge of 6.25 x 1018 electrons or protons.

Example After charging a piece of fabric, Jonathan calculates that it has lost 2x1015 electrons. a) What is its charge in coulombs? 2x1015 electrons/ 6.25x1018 = 0.00032 C b) Is this charge positive or negative?

Forces of Attraction and Repulsion Similar electric charges (two positive charges or two negative charges) repel each other Opposite electric charges (one positive and one negative charge) attract each other

Forces of Attraction and Repulsion electric force- force that permits the attraction or repulsion between charges law of conservation of charge- electric charges can not be created nor destroyed; they can only be transferred from one object to another

Most objects are electrically neutral [equal numbers of positive and negative charges (protons and electrons)] We can however give a charge to an object by transferring electrons from one place to another (electrification).

Electroscope

Conductors and Insulators a substance that permits charges to circulate freely Ex: metals, electrolytic solutions Insulators a substance that does not permit charges to circulate freely Ex: wood, plastic, glass, paper, ceramic, rubber, silk, air

Semi-conductors conductibility depends on different factors Often used in electronics Ex: carbon, metalloids

Static Electricity phenomena linked to charges at rest

Charging by Rubbing When two objects are rubbed together, certain atoms from one take the valence electrons of the other. This results in two charged objects with opposite signs.

Charging by Rubbing Affinity Substance High affinity to receive electrons (tendency to become negatively charged)   High affinity to donate electrons (tendency to become positively charged) Plastic Gold Nickel, copper Rubber Sulfur Wood, yellow amber, resin Cotton Paper Silk Lead Wool Glass

Charging by Conduction charge an object by placing it in contact with another object that is already charged. The charges are shared between the two objects. The result is two charged objects with the same sign but the charge is weaker than in the original object.

Charging By Induction action that occurs without direct contact charged object comes close to a neutral object, without touching it charges with opposite signs progressively accumulate on the side close to the charged object. At the same time, if the second object is a conductor, an equal number of opposite charges accumulates on the other side of the object, conforming to the law of conservation of charge.

Charging By Induction

In class work p.172 # 1,2,3,7,8