1. Static Electricity Notes
CP Physics

2. Electrical Forces
Created by the attraction and repulsion of charged particles (ions)
Part of electromagnetic force

3. Electromagnetic Forces vs. Gravitational Force
Attraction or repulsion between two charged objects
Can act over a distance (two objects do not have to touch)
Stronger than gravitational force
Attractive force only between two objects
Can act over a distance (two objects do not have to touch)
Weaker than electromagnetic force (weakest of four universal forces)

4. Fundamental Rule of Electrical Phenomena
Like charges repel
Opposite charges attract

5. Charged Objects Objects become charged when electrons are removed
Ions = charged atoms
Atoms lose electrons = positive ion
Atom s gain electrons = negative ion
Materials that become negatively charged
Rubber
Silk
Materials that become positively charged
Glass
Hair
Fur
Plastic

6. Conservation of Charge
Cannot create or destroy charges, can only transfer charges from one material (object) to another
Actually separating charges to form (+) and (-) charged objects
Note: charges cannot be divided, they always move in whole numbers

7. Coulomb’s Law
States that electrical force varies inversely with the square of the distance and directly with the product of the charges
Unit of charge = Coulomb (C)
Electrical forces between very large objects tend to cancel out, but electrical forces between very small objects (atomic level) can be very large
Equation:
Fel = kQ1Q2 k = 9.0 x 109 N•m2/C2 d2
Q = charge in coulombs, d = distance in meters, k = constant

8. Conductors and Insulators
Conductors: outer electrons move easily, have loosely held electrons, ex. Metals
Insulators: outer electrons held tightly so they do not move easily, ex. Glass, plastic, rubber, wood
Semiconductors: materials that are usually insulators but when impurities added become conductors, ex. Silicon, germanium
Superconductors: materials with no resistance to electrical flow – do not lose any energy to friction or heat, most work at absolute zero (-273 oC)

9. Charging Objects: Friction
Rubbing two surfaces together transfers electrons
Results in a (+) object and a (-) object
Two objects are attracted to each other
Ex. Clothes in dryer, combing hair

10. Charging Objects: Conduction
Touching a neutral object with a charged object results in the neutral object taking on the same charge. The two objects then repel each other. Until the objects are grounded, this form of charging is permanent.

11. Charging Objects: Induction
Bring a charged object near the neutral object. Charges within the neutral object separate so that the side closest to the charged object takes on the opposite charge and is attracted to the charged object. This process is only temporary unless the object can be divided as in steps c and d shown below.

12. Grounding
Process of touching an object so that a path to the ground exists and charges can move from the object into the ground.

13. Lightning
Electrical discharge between oppositely charged clouds or the ground
Results from charging by induction – negatively charged clouds induce positive charge in ground below them

14. Charge Polarization Occurs in insulators
Charged object near insulator causes charge rearrangement within atoms or molecules
Atoms – electrically polarized – one side of atom is slightly positive while opposite side is slightly negative
Ex. Balloon rubbed against hair will stick to the wall

15. Charge Polarization: Water
Many molecules are electrically polarized in their natural state. One example is water – the oxygen atom has a slight negative charge while the side of the molecule with the hydrogen atoms is slightly positive.