Electrostatics

• Energy at rest - study of nonmoving electric charge.

• Static Electricity.

• Involves– Electric charges– Forces between them– Their behavior in material

• Atoms – electrons

• Energy associated with electrons that move from one place to another.

Form of EnergyForm of Energy

• Charge – gain/loss of e-.

• Force – when charge particles come near one another.

• Rule: “Like charges repel, unlike attract”

Electric Charge/ForceElectric Charge/Force

• Region surrounding charged particles.• Strength as distance of particle

Electric FieldsElectric Fields

Charged Particles

• Ion - a charged atom caused by an imbalance of p+ and e-.– positive ions have lost e-– negative ions have gained e-

• The amount of energy required to tear an electron away from an atom varies for different substances.

Triboelectric Series

• Ranks materials according to their tendency to give up their electrons.

THE TRIBOELECTRIC SERIES

PositiveRabbit’s fur

Glass

Wool

Cat’s fur

Silk

Felt

Cotton

Wood

Cork

Rubber

Celluloid

Negative

Law of Conservation

• Conservation of Charge - electrons are neither gained nor destroyed, but are simply transferred from one material to another.

• Metric unit for electric charge (C).

• The symbol for charge is (q).

• One Coulomb is the charge of 6.24 x 1018 electrons – about the charge going thru a 100 watt light bulb in about 1 second.

Coulomb

Coulomb’s Law

• For charged particles, the force between the charges varies directly as the product of the charges and inversely as the square of the distance between them.

• Fel = kq1q2

d2

k = 9.0 x 109 N-m2/C2

• Build up of electric charges.

• Methods– Friction– Conduction– Induction

Methods of ChargingMethods of Charging

Conduction

• Conductors - materials where the outer electrons are not anchored to the nuclei of a particular atom, but are free to roam.

• Insulators - materials where the outer electrons are tightly bound to the nuclei and remain with a particular atom, they are not free to roam.

Semi-Conductors

• Materials which are good insulators in pure crystalline form, but conduction tremendously increases when an impurity has been added.

• Examples: germanium and silicon.

• Uses: transistors and diodes.

Superconductors

• Certain materials (metal alloy and ceramics) that acquire infinite conductivity (zero resistance to the flow of charge) at temperatures near absolute 0.

• Examples: Mercury, Niobium-Tin, Lanthanum-Barium-Copper Oxide, and Yttrium-Barium-Copper Oxide.

Induction

• Electrons will move in the conduction surface of an object when a charged object is near it. Excess electrons in the conduction surface will transfer onto another surface.

• Brings opposite charges

• Electric discharge.

• Loss of static electricity as electric charges move off an object.

• Grounding – lightning rod

LightningLightning

Electroscope