A charge is when an object is either positive or negative. It is important to remember that like charges will repel each other. And opposite charges will always be attracted to each other. CHarges are transferred through: friction, contact, and induction.
Polarization is the sharing of electrons and protons. If an object is polar it means that the object has both positive and negative charges.
So why does plastic wrap stick to ceramic and glass bowls but not metal bowls?
-Because of COULOMBS LAW: the force between any two objects is inversely proportional to distance
1.) Plastic wrap is charged by friction and when brought near the bowl the bowl polarizes
2.) The positive charges in the bowl move close to negative the plastic wrap and the negative charges between the like repelling charges
3.) The distance between the opposite attractive charges is smaller than the distance between the like repelling charges
F=K(q1q2/d^2)
Since there is a greater distance between the repulsive forces, the force between them will be less than the closer attractive forces thus the plastic wrap sticks to the bowl.
Another good question related to polarization and Coulomb's law is:
Why does our hair stand up after taking a sweater or hat off?
-Because the sweater/ hat will steal all of the protons leaving only electrons left which will then repel each other since they are like charges causing your hair to stick up
Electric Fields
An electric field is the area around a charge that can influence another charge. Positive charges have arrows pointing outward because they will repel any positive charge and electrons have arrows pointing inward because they are attracted to protons. As a charge moves away from the electric field the force becomes weaker and the field shows this by getting further apart.
OHM'S LAW
States that voltage is directly proportional to current times resistance.
And in order to figure out the force of an electric field you say the electric field=the amount of force per coulomb.
What is Electric Shielding?
-if you are inside a metal container the forces counter act because they are pulling from every direction so that no force is felt
SO then why are electric devices put in metal containers?
-so we keep the positive charges where they are because you don't want any negative charges near them
Electric Potential/ Electric potential Difference/ Ohm's Law and Capacitors
OHM'S LAW
States that voltage is directly proportional to current times resistance.
And in order to figure out the force of an electric field you say the electric field=the amount of force per coulomb.
-So when there is more current the resistance is less but when there is more resistance the current will be less.
-The Potential difference is when the circuit is completed. There must be two unlike charges which are different that must be attracted to each other to form a circuit. Without potential difference there would be no way for the current to travel through the circuit because there would be no circuit. Voltage is also potential difference per charge
PE/charge
V= change in PE per charge
measured in Volts
A conductor is used in order to create more resistance so that less current will flow through.
Types of Current, Source of Electrons, Power
Current is the flow of charges through a circuit. Current is measured in amperes and in order to find current you use Ohm's law which is V=IR.
There are two types of current which are AC and DC
AC stands for alternating current which is when the flow of electrons switches from forward to backward.
DC stands for direct current where the flow of electrons is direct and only flows in one direction.
The electrons which flow through the current are not supplied through power but they are already there. Power is the amount of voltage in the current.
Power=VI
Power companies don't sell power like their name implies but they sell energy.This energy is used in current. They do not sell electrons because electrons are already there and they do not sell power because power is what is generated.
In order for there to be a current though there must be a potential difference and the circuit must be completed.
**Flashlights**
Why do flashlights get dimmer as the batter becomes weaker?
-Because as the batter becomes weaker it means that the current is less because the voltage is lowered. With let current means there must be more resistance so the light will become weaker.
Why do bulbs often blow when they are first turned on?
-Because when bulbs are first turned on the filament is generally really cold so the hot current flowing through will be so hot there is little resistance causing the bulb to go out. But as the heat in the filament increases the resistance will increase so that the bulb will not blow out.
Parallel and Series Circuits
A Series circuit is a circuit which looks likes:
Where the current travels straight through both of the lightbulbs. The resistance in a series circuit goes up as more appliances are added, which then causes the current to go down as more appliances are added, then causing the brightness to go down as more appliances are added. If a lightbulb were to stop working in a series circuit then the will all go out. This is because since they all have the same current running through them they will all go out if one bulb were to be removed. Series are not used in homes because of this fact.
A Parallel circuit looks like:
The current is divided into two different paths in a Parallel circuit. The resistance will go down as more appliances are added causing the current to increase as more are added to the circuit. The brightness will stay the same though because voltage is the exact same for each branch in the circuit. If one of the bulbs were to go out though they are not all effected because they each have their own branch with the same amount of voltage. This is why they are used in most households.
How is fuse wired and how does it work?
-They are used if the current gets too high it could overheat and the wiring could cause a fire so fuses/circuit breakers are used to protect. At a certain current level they shut off all of the power from the circuit. In order to do this they must be wired in series with the rest of the circuit. fuse blows by melting the wire inside. Fuses protect your house because when the circuit overheats the fuse wire will melt so that the current will not pass through the circuit.
This unit has been the hardest unit so far for me. I have really struggled with my understanding of almost all of the different topics. It took me a while to grasp current in particular. Once I did though and I went in to conference period a few days I felt a lot better. I think that my effort has been pretty solid but not as good as it could be. I think that what I could do in the future is take better notes, because for some reason my notes for this section were a little disorganized. I am expecting to do well on this test but again this unit was particularly hard for me.
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