ELECTROSTATICS Static Electricity Static electricity the accumulation of

ELECTROSTATICS

Static Electricity Static electricity - the accumulation of excess electric charges on an object Only electrons move

Electrostatic Rules All charges are surrounded by electric fields • Any charge placed in an electric field will be pushed or pulled by the field (experience a force)

Opposite charges attract Similar charges repel Charges can act at great distances Electrostatic force is a very strong one

What is Going to Happen? +++ ---

What is Going to Happen? --- --

Field Lines • Field Lines cause force just like gravitational field lines -

Field Lines • Electric field lines always point towards a negative charge • Electric field lines always point away from a positive charge

Strength of a Field • Strength of an electric field can be determined by the force on a positive test charge placed in the field • The strength of a field increases as the test charge gets closer to the field • Calculated with E=F/q

Field Lines - +

Law of Conservation of Charges may be transferred from object to object but it cannot be created or destroyed

Conductors & Insulators • Conductors- Materials that easily transfer electrons – Metals (Copper) • Insulators- Materials that do not transfer electrons easily – plastic wood rubber and glass

Transferring a Charge • Three main methods –By Contact –By Induction –By Static Discharge

Charging by Contact • Done by touching or rubbing • Example: feet rubbing the carpet

Charging by Induction • Electrons move because of a nearby charged object • Example: negatively charged balloon near your sleeve causes your sleeve to be positively charged

Charging by Induction • How does a balloon stick to the wall or ceiling to “defy” gravity?

Static Discharge • A transfer of charge through the air between two objects because of the buildup of a static electricity – a spark! • Example: lightning

Coulomb’s Law q 1 q 2 FE=k d 2 FE is the electrostatic force (Newtons) q 1 and q 2 are charges (coulombs) d is the distance between the charges k = coulomb’s constant = 9 X 109 N m 2/c 2 1 Coulomb of charge = 6. 24 X 1018 e-

Relationship of Electrostatic Force and Distance • Recall the Inverse Square Law • Ex: If the distance between A & B is doubled, by what factor does the Force change?

Energy of Charged Particles • The energy of charged particles in an electric field can be calculated as • UE=q. V • Where q is the charge and V is the potential or voltage it experiences in the field

Questions: 1. Which particle is responsible for electrostatic forces? 2. Which method of transferring charge is by direct contact? 3. Field lines flow away from ___ charges and towards ___ charges 4. When placed between the positive and negative terminals of a discharge tube, which would move toward the positive terminal?

Questions: 5. What happens when a rubber rod is rubbed with a piece of fur, giving the rod a negative charge? (where do the e- move to? ) 6. If you ½ the distance of 2 charged particles, what happens to the strength of the force? 7. Give an example of an insulator. 8. Lightning is an example of ?