Electric Charge. MATTER AMBER a hard translucent fossil resin varying in color from yellow to light :Amber.pendants.800pix.050203.jpg.

Electric Charge

MATTER

AMBER

a hard translucent fossil resin varying in color from yellow to light

http://commons.wikimedia.org/wiki/File:Amber.pendants.800pix.050203.jpg

http://witchcraft-supplies.com/Prod4/amber_insect1.jpg

BENJAMIN FRANKLIN

INTRODUCED THE IDEA THAT ALL SUBSTANCES ARE PENETRATED BY AN ELECTRIC FIRE

TOO MUCH ELECTRIC FIRE= POSITIVE CHARGE

LACK OF ELECTRIC FIRE= NEGATIVE CHARGE

Electrostatics

The study of the interactions

between electric charges that

are at rest (or nearly so).

ELECTRIC CHARGE

Fundamental quantity in electrostatics

Two kinds of charge: positive and negative

Elementary Charge

Ce 1910602.1 ×=

Electric Attraction and RepulsionLIKE CHARGES REPEL: Two positive charges repel each other

Two negative charges repel each other

UNLIKE CHARGES ATTRACT:

Negative charge attracts positive charge.

Law of Conservation of Charge

• THE NET AMOUNT OF CHARGE PRODUCED IN ANY PROCESS IS ZERO;

• NO NET ELECTRIC CHARGE CAN BE CREATED OR DESTROYED

Conductors, Insulators, and Ground

Conductor- material that permit the flow of electric charge

Insulator- material that do not allow the flow of electric charge readily

Ground- a neutral material that can accept or supply an essentially unlimited number of charges

PLEASE SEE VIDEO DEMONSTRATION

CHARGING PROCESSCONDUCTION- charging neutral object by placing charge object in contact with the neutral object

INDUCTION- charging neutral object by placing charge object near the neutral object without physical contact

INDUCTION PROCESS

INDUCTION PROCESS

ELECTROSCOPE

• A device that can be used for detecting charge

a,a- - thin leaves of metal foilb - metal supportc - glass container d - metal knob

COULOMB’S LAWApplicable to point charges

(objects whose size is much smaller than the distance between them)

Describes the interaction of electric

chargesforce) electric theof (magnitude 2

21

r

qqkF=

[m])(meter charges b/w distance -r

[C]) 2(Coulombobject of charge -q

[C]) (Coulomb 1object of charge -q

10 9.0 ≈

constant sCoulomb’ -k

[N])(Newton force ticelectrostaforce/ electric -F

where

2

1

22 9 CmN×

EX 1. ELECTRIC FORCE ON ELECTRON BY PROTON

Determine the magnitude and direction of the electric force on the electron of a hydrogen atom exerted by the single proton that is the atom’s nucleus. Assume the average distance between the revolving electron and the proton is r= 0.53 x 10-10 m.

Two point charges, q1= +25nC and q2= -75nC, are separated by a distance of 3.0 cm. Find the magnitude and direction of

a) The electric force that q1 exerts on q2; and

b) The electric force that q2 exerts on q1.

EX 2. WHO IS STRONGER?

PRINCIPLE OF SUPERPOSITION OF FORCES

States that when two or more forces exerted by two or more charges on a charge, the total force on that charge is the vector sum of the forces exerted by the individual charges.

N

N

i

FFFFF→

3

→

2

→

1

→

1

→

....∑ ++++==

Two point charges are located on the positive x-axis of a coordinate system. Charge q1 = 1.0 nC is 2.0 cm from the origin, and charge q2 = - 3.0 nC is 4.0 cm from the origin. What is the total force exerted by these two charges on a charge q3 = 5.0 nC located at the origin? Gravitational forces are negligible.

VECTOR ADDITION OF ELECTRIC FORCES ON A LINE