Physics-reviewer.docx

PHYSICS Electricity- comes from the word “electron” which means amber.

#electrons= _q total_ 1.6x10-19

Amber effect- literally called static electricity Benjamin Franklin-made the arbitrary choice of calling the positive and one negative. 

“an equal amount of the opposite charge is produced on another object when a certain amount of charge is induced on one object”

Electrostatics- study of charge that can be localized and contained. Studies electric charges at rest. Electric Charge   

Electric charge is conserved and it is quantized with units of e. An atom that loses an electron becomes positively charged(positive ion) Atom that gains an electron becomes negatively charged(negative ion) Some material may be polarized such their atoms interchange in response to an external charge.

Charge Concepts- opposite charges attract, like charges repel Law of conservation of Charge  The total amount of electric charge produced in this process is zero  Symbol: q, Q  Unit: C , Coulomb named after Charles De Coulomb  Our body contains more than 1X1028  The net charge of an object is the

excess of any charges as a result of the transfer of electrons  Essential principle in electrical phenomena is the conversation of charge; The total charge of an isolated system remains constant

Particle electron

Charge(c)

proton

1.6x10-19

9.109x1013 1.673x10-27

neutron

0

1.675x10-27

-1.6x10

-19

Mass(kg)

Ways to charge a neutral object by : 1). Conduction- interaction occurs between charged object and neutral object Consequence: two objects with the same charges 2). Induction- no interaction occurs between charged object and neutral object Consequence: two objects with opposite charges 3). Friction: Rubbing two materials together can rub electrons off from one object to another. Conductor  Materials that allow electrons to pass through them.  Metals are naturally excellent conductors because their valence(outer shell) electrons are not confined to any one atom.  Electrons are free to roam on metal object.  If a conductor carries excess charge, the excess is distributed over the surface of the conductor. Insulator  Materials that hinders the flow of electrons and atoms are tightly bond.  Non-metals are mostly insulators



Insulators are useful for studying electrostatics.  Electrons are not free to roam on nonmetallic objects. Semi-Conductor  Materials that are considered neither good conductors nor insulators.  Their properties change with their chemical composition.  Photoconductive materials become conductor when light shines of them. Super Conductor  Material that considered as perfect conductors of electricity. ____________________________________ Coulomb’s Law  In 1778, a French physicist Charles Augustine de Coulomb formulated the relation between charged particles which is called Coulomb’s law.  States that ”the magnitude of the electric force between two-point charges is directly proportional to the product of the charges and indirectly proportional to the square of distance that separates them” Mathematically can be written as:

Fe= k Q1 Q2 r2 where… Fe = electric force(N)

Q1 Q2= electric charge(c) r= distance between 2 charges(m) k= coulomb constant= 9x109 Nm/c2 or 8.998x109 Nm/c2

Electric Fields  a region of space in which an electric charge will experience a force when placed on it.  An electric field may be produced by one or more charges and it may be uniform or it may vary in magnitude, direction or both, from place to place. Electric Field Intensity  Coulomb force per unit charge the electric field exerts on a positive charged placed in the region of the field. Mathematically can be written as: E= _F_ or E= Q1 Qt r2 Where is…  E= electric field(N/C)  F= electric force(N)  Qt= test charge(c) Electric Flux  Defined as the rate of flow of the electric field through a given area. Gauss’s Law  Powerful tool for the evaluation of electric fields when they are produced from charge distributions of enough symmetry to apply it.