ELECTRICITY

and COULOMB’S LAW

Created byKurnia Ika Pangesti

THE FACT OF CHARGE

• There are two kinds of electric charges, which were given the names positive and negative

• Charges of the same sign repel one another and charges with opposite signs attract one another

• Positive charge comes from having more protons than electrons

• Negative charge comes from having more electrons than protons

• Charge is quantized, charges occur in integral amounts of the fundamental unit of charge e

• Electric charge is always conserved

The Law of Conservation of Charge

Charge can be created and destroyed, but only in positive-negative pairs.

The Law of conservation of charge states that the net charge of the two objects of the isolated system remains constant

Electrostatic ChargingMaterial category depending on the ability of electron to move trough the material:1. Insulator2. Semiconductor3. Conductor

Electrostatic ChargingThere are three ways that object can be given a net charge, these are:1. Charging by Friction2. Charging by Conduction3. Charging by InductionElectrostatics is the science of static or stationary electricity. Electrostatics operates in electrical insulators, and this is where it differs from current electricity that needs electrical conductors to facilitate electron flow.

Coulomb’s LawThe force exerted by one point charge on another acts along the line betweenthe charges. It varies inversely as the square of the distance separating the charges and is proportional to the product of the charges. The force is repulsive if the charges have the same sign and attractive if the charges have opposite signs.The magnitude of the electric force exerted by a charge q1 on another charge q2 a distance r away is thus given by:

Where the constant k = 8.99 x 109 Nm2/C2 and r is the distance between the charges.

The law expressed in vector form for the electric force exerted by a charge q1 on a second charge q2 , written F12, is

The form of the electrostatic force should remind you of something

that you have already seen before: Gravity.

Recall that the gravitational force is:

where G = 6.67 x 10-11 Nm2/kg2

Compare this to the electrostatic force:

  where k = 8.99 x 109 Nm2/C2

Parallel between Electrostatic and Gravitational Field

Parallel between Electrostatic and Gravitational FieldSimilarities between electrostatic and gravitational forces:

1. Both act in a vacuum.

2. Both are central and conservative.

3. Both obey an inverse-square law (both are inversely proportional to

square of r).

Parallel between Electrostatic and Gravitational FieldDifferences between electrostatic and gravitational forces:

1. Electrostatic forces are much greater than gravitational forces for natural

values of charge and mass. For instance, the ratio of the electrostatic force

to the gravitational force between two electrons is about 1042.

2. Gravitational forces are attractive for like charges, whereas electrostatic

forces are repulsive for like charges.

3. There are not negative gravitational charges (no negative mass) while there

are both positive and negative electric charges. This difference, combined

with the previous two, implies that gravitational forces are always attractive,

while electrostatic forces may be either attractive or repulsive.

Thank You