HMWK for Wed: Read p .400-405, p. 405#1-7
Today we had a warm up: Your blanket takes some e- from you. You are now ____ and your blanket is now ___.
Notes: Metals vs Nonmetals and Grounding vs. Insulating:
Metals and Nonmetals vary mainly based on how they treat their electrons.
Metals have relatively few p+ in the nucleus, and can't hold e- very tightly/closely. This makes their e- free to come and go, and also makes metals relatively big atoms. The loose grip on e- makes metals good conductors.
Nonmetals have larger numbers of p+ in the nucleus and hold e- more tightly. This means smaller atoms and electrons that are not able to move very freely. This makes nonmetals generally good insulators.
Grounding is when an object is connected to the Earth by a conductor. The round plug in a 3-prong electrical outlet is the "ground" and is connected to a home's copper plumbing, and... the Earth. This grounding has multiple reasons; motorized electronics, if there is a short or a static electrical discharge, dissipate this electricity to the Earth and not a person. Second, a person touching a computer, etc. won't cause the internals to get damaged because they're sealed inside a grounded metal cage.
Insulating is kind of opposite from grounding... not exactly. Insulating is keeping an object from contact with other conductors (or the Earth). It's accomplished with nonmetals; plastics, rubber, AIR, etc. Insulators CAN allow e- to move, just not as easily as metals do. The more push the e- have (voltage), the more likely e- are to move. Your skin is a good enough insulator to hold a 1.5V battery in your hand, but it's not really safe to go grabbing 120V or 240V wires; they will conduct through you!
We will review insulation with the Van de Graff generator; 500kV will jump through your shoes and into the floor like they weren't there. :)
Other stuff from today: Ranking tasks WS relating electric force between particles with different charge and spacing (see me for a copy) and induced charges.
Video and demonstrations on the Wimshurst Electrostatic Generator.
Tomorrow (Tues) we will have an algebra quiz to help you decide whether to take Honors chemistry or regular Chemistry next year (signups are soon!) , we will have some brief notes regarding how charges behave on conductors, and demonstrations (some hands-on!) with the Van de Graff electrostatic generator.
Notes on charge distribution: Charge spreads over the surface of conductors; the electric field inside a conductor is zero. If you've ever tried to use a cell phone in an elevator or metal building (seckman HS), you have experienced this!
On the surface, charges repel each other and tend to spread out over the surface. For a spherical object, each charge pushes on the others with equal force and there is little net force on each charge (the larger the sphere, the closer this net force gets to zero)
With a pointed object, charges close to the point are repelled by others away from the point unevenly; they have nothing pushing them back, so they experience a net force pushing them off the object. For this reason, you are more likely to receive a shock when approaching a doorknob with your finger than a whole hand; charges accumulate and push toward the point.
This idea is manipulated with lightning rods; pointed rods that protect buildings from lightning. Charges accumulate on the points and make strikes less likely to hit other objects.... at the same time, charge "leaks off" the rods, making lightning less likely in the first place.
We experienced charging by induction and contact with the Van de Graff generator and got to play with rounded vs. pointed approaches for lightning rods a bit. Wednesday we'll have more; an insulated platform for those who don't want to feel any shock but would like to be charged!
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