Unit 6 – Static Electricity

1.21 gigawatts of electrical power

I. Static Electricity: the study of electrical _______________ that have _______________ . charges come to rest Atoms are made up of: electron e- - ________________________ charged proton p - __________________________ charged neutron n - ______________________ negatively positively uncharged q The symbol for electric charge = _________ UNITS for q: 1 elementary charge e = equal in magnitude to the charge on the _______________ or the __________________  Notice that the symbol e- is different from e. electron proton The charge on 5 electrons is written: q = ___________ The charge on 3 protons is written: q = ___________ The charge on 2 neutrons is written: q = ___________ -5e +3e

No single, isolated charge has ever been found that is smaller than 1 ____ . You cannot have a charge of _________ or __________ on an isolated particle or object, but you can have any integer multiple of it. e (1/2)e -13.7e In practical use, a bigger unit is used for charge: 1 coulomb C = __________________ elementary charges So you could write 4 coulombs as: q = 4C = _________________ e = __________________ e It is possible to have a fraction of 1 C. For example, 0.5 C = _____________________ e = ________________________________ e , because it is still an integer # of elementary charges. 6.25 x 1018 2.5 x 1019 25 x 1018 3.125 x 1018 3,125,000,000,000,000,000

What's in your wallet? 6.25 TIMES 10 TO THE 18TH NEVER ELECTRON I.N. ATOM

charged neutral Objects become _________________ when _____________ objects _______________________________ . gain or lose electrons has lost electrons positive ion/object - _______________________________ negative ion/object - ______________________________ has gained electrons A B C 9 # of + q: _____ # of - q: _____ net q = _____ 5 # of + q: _____ # of - q: _____ net q = _____ # of + q: _____ # of - q: _____ net q = _____ 6 2 5 7 +7 -1 Here, q = +7 means ______ and q = -1 means ______ +7e -1e B has ________________ and so is ______________ charged C has ________________ and so is ______________ charged lost 7 e- positively gained 1 e- negatively

Two basic types of materials: __________________ - its electrons can move easily - best examples are _______________ 2. ___________________ - its electrons cannot move easily There are three basic ways to _______________ charge: __________________ - by rubbing two __________________ _________________ - by touching two __________________ _________________ - by bringing a ______________ object near a conductor conductors metals insulators

Insulators: Plastic Lots of Plastic

Conductors:

Conductors: metal

Two basic types of materials: __________________ - its electrons can move easily - best examples are _______________ 2. ___________________ - its electrons cannot move easily There are three basic ways to _______________ charge: __________________ - by rubbing two __________________ _________________ - by touching two __________________ _________________ - by bringing a ______________ object near a conductor conductors metals insulators transfer friction insulators contact conductors induction charged

Charging by friction (rubbing two insulators together) requires ________ because the charges are not __________ __________ . work free to move neutral ________ plastic straw __________ wool neutral rub together, then separate. charged ________ plastic straw charged __________ wool The charges are ______________ on each object. Also, they are not ______________________ in either object even though the like charges __________ each other. This is because charges cannot move freely in ___________________. opposite evenly spread out repel insulators

Ever get that shock when getting out of your favorite car seat? Now use…

Charging by contact (by touching two conductors): the electrons are __________________ . They arrange themselves _____________________________________________________ because of _______________________________ . free to move as far as possible away from each other electrostatic repulsion metal ________sphere plastic _________ base __________ neutral _________ charged neg. _________ charged pos.  The charges are _____________________ over the sphere. spread out Ex. Touch a negative sphere to a neutral one: Before:

Touch: The charges _______ each other and some of them ______ ____________________ . repel move to the other sphere Separate: evenly distributed The charges are _______________________ because they are ____________________ . The neutral object has become charged with the ____________ type of charge as the charged object. free to move same

Static Electricity is used in pollution control: The same idea is used in some air fresheners.

You say you love your computer, but are you ready to make a…. commitment?

Charging by induction: Bringing a ___________object near a neutral conductor ____________ a charge separation. charged induces Before: _______ object neutral neutral still _______ but charges are _________ Bring charged object near ________________________ : but not touching separated Now allow some of the ______________ charges to escape. separated wire "ground" Now separate spheres: Sphere now has ______________ charge! opposite

cloud with separated charges negative charges are driven deep underground neutral ground ground is still neutral

Ben Franklin’s lightning rod….used. Lightning rods allow charges to drain off before they build up enough to cause a strike. rod wire

Charge up the paint drops negatively. Charge up the part you want to paint positive. Then you can paint the car with: …less mess …less waste …less skill …more even layers of paint

Whenever charges are __________________ , the total amount of charge involved always ____________________ . This is called the Law of ___________________ of Charge. _________ q before = ________ q after transferred remains the same Conservation total total Ex 1: Two identical metals spheres are touched together. What is the charge on each after they are separated? (Assume any excess charge spreads itself out equally over the two spheres after touching.) A B A B touched then separated ? ? +2C -8C qA' + qB' qA + q B =

+2C + -8C = qA' + qB' -6 C = -3 C + -3 C Each sphere will have half of the total = _________ C Sphere A: +2C  ______, so it ____________________ Sphere B: -8C  ______, so it ____________________ -3 C gained 5 C of e- -3 C lost 5 C of e- -3 C Ex 2: Two identical metals spheres are touched together. What is the charge on sphere B before it is touched? (Assume any excess charge spreads itself out equally over the two spheres after touching.) A B A B touched then separated -5 C ? -1C ?

qA + q B = qA' + qB' -1C + q B = -5 C + -5 C -1 C + -9 C = -10 C So sphere B had = _________ C before it touched. Sphere A: -1C  ______ C, so it ____________________ Sphere B: -9C  ______ C, so it ____________________ -9 gained 4 C of e- -5 lost 4 C of e- -5 Ex 3: Two insulators are rubbed together as shown below. What is the charge on B after they are rubbed? (Do NOT assume any excess charge spreads itself out equally—they are not identical metal spheres.) A B A B touched then separated ? +2e +15e +9e +15e

qA + q B = qA' + qB' +15e + +2e = +9 e + qB' +8e = qB' Object B will have = _________ e Object A: +15e  ______, so it ____________________ Object B: +2e  ______, so it ____________________ 8 +9 e gained 6 e- lost 6 e- +8e Ex 4: Two insulators are rubbed together as shown below. What is the charge on A before they are rubbed? (Do NOT assume any excess charge spreads itself out equally—they are not identical metal spheres.) A B A B touched then separated +10e -7e -6e ?

qA + q B = qA' + qB' -6 e + +10e qA + -7e = qA + -7e = +4e qA +11e = +11 Object A had = _________ e Object A: +11e  ______, so it ____________________ Object B: -7e  ______, so it ____________________ -6 e gained 17 e- lost 17 e- +10e