Static Electricity

Define some of the major ideas about static electricity

Static Electricity

Electricity “exists” because of two types of charge Charge is (+) or (-) Fundamental unit is the charge of one electron = one proton =

1.6 x 10-19C Unit of charge is the Coulomb. One coulomb is a boatload of

electrons Like charges repel, opposites attract Charge is Quantized, you can’t have ½ of an electron charge.

Can’t break the charge on one electron any smaller.

Static Electricity

Ways to charge objects include: Friction, like rubbing the fur on plastic Conduction, touching a charged object to another

object Induction, like in the lab (which maybe didn’t work

too well). Bring a charged object next to a conductor and then “ground” the conductor, leaving it charged.

Static Electricity

Insulators: electrons are held tightly and can’t move around easily, so electricity doesn’t move through them. Examples are rubber, plastic, glass

Conductors: charge (electrons) moves easily. Examples are metals: copper, aluminum, gold

Static Electricity

Electric Force You saw the tape attract or repel, what causes things to

move? (rhymes with horse) There is an electric force between any 2 charged objects

called the Coulomb Force Force depends on the amount of charge on each object

and on the distance between them. This force is analogous to the Universal Gravitational Force. Can you write the equation for these?

Electric Force

Coulomb’s law for electric force

F = (kq1q2)/r2

q = amount of charge in coulombs r = distance between charged objects k = Coulomb constant = 9x109

The force is the same on both charged objects (remember forces exist in pairs, Newton’s 3rd law)

Electric Force

The electric force is conceptually much bigger than the gravitational force.

Why don’t we see the “electric force” much? Objects in our world are typically neutral

(even number of electrons and protons)

Electric Field

Much like the concept of an invisible Gravitational Field, there exists an invisible electric field around any charged object.

The Electric field is defined as the Force that another charged object (test charge) would feel in the presence of the source charged object divided by the amount of the charge on the test charge

E = F/q = kQq/r2q = kQ/r2

Electric Field Lines

Electric field lines surround a charged object and point in the direction that a positive (+) test charge would be forced to move