- Charges and Polarization (Coulomb's Law)
- Electric Fields
- Electric Potential/Electric Potential difference, Capacitors
- Ohm's Law and electric potential difference
- Types of Current, source of electrons, Power
- Parallel and Series Circuits
Charges and Polarization:
The three ways we learned how to make something neutral or to have a charge is by:
- Direct contact
- Friction (When objects rub against each other)
- Induction: Way to charge without contact by bringing a charged object next to a negative object.
One of the big questions related to this topic was, why does hair stand up after putting on a sweater? The answer to this question is that when the sweater rubs against your hair it steals electrons from it (friction) moreover, the sweater becomes negatively charged, leaving your hair to be positively charged. The hair stands up due to it's attraction to the sweater (positive and negative charges attract).
Polarization: When an object becomes polar charges separate to opposite sides of an object (object is still neutral)
Coulomb's Law: States that the force between 2 charges is inversely proportional to the distance (the greater the distance the weaker force)
Electric Fields:
Electric fields refers to the space around around every electrically charged body. Electric fields have both magnitude (force per unit of charge) and direction. The equation used for calculating the force a body is experiencing in space is E = F/q. The electric field is depicted with vector arrows which show the direction positive charges move.
An important thing to note about electric fields which make them different from gravitational fields is they electric fields can be shielded by various materials. For example charges inside a metal box stay is the same position because there is no force pulling them in one direction. The balance of positive charges around the box keeps everything in place (net force inside the box is zero).
Electric Potential, Electric Potential Difference, and Capacitors
Electric potential energy is the energy a particle possesses by virtue of its location. If one was to push a charged particle against the electric fields then the work changes the electric potential energy of the charged particle. If this particle was to be released then its potential energy changes into kinetic energy. When considering charged particles it is easier to consider the electric potential energy per unit of charge (per coulomb) A object with 12 coulombs of charge as a specific location has 12 times as much potential energy than a object with 1 coulomb of charge. But 12 times as much electric potential energy for 12 times as much charges is the same as 1 electric potential energy per 1 coulomb of charge.
Here is what a series circuit looks like
An important thing to note about electric fields which make them different from gravitational fields is they electric fields can be shielded by various materials. For example charges inside a metal box stay is the same position because there is no force pulling them in one direction. The balance of positive charges around the box keeps everything in place (net force inside the box is zero).
Electric Potential, Electric Potential Difference, and Capacitors
Electric potential energy is the energy a particle possesses by virtue of its location. If one was to push a charged particle against the electric fields then the work changes the electric potential energy of the charged particle. If this particle was to be released then its potential energy changes into kinetic energy. When considering charged particles it is easier to consider the electric potential energy per unit of charge (per coulomb) A object with 12 coulombs of charge as a specific location has 12 times as much potential energy than a object with 1 coulomb of charge. But 12 times as much electric potential energy for 12 times as much charges is the same as 1 electric potential energy per 1 coulomb of charge.
The unit of measurement for electric potential is volt, therefore another name for electric potential is voltage.
Electric energy is stored in a device called a capacitor.
What is a capacitor?
A capacitor is a pair of conducting plates separated by a
small distance; the plates are connected to a charging device such as a
battery. The capacitor plates have equal and opposite charges when electrons
are pumped through the battery onto the opposite plate. The charging of the
plates in done when the potential difference between the plates equals the
potential difference between the battery terminals.
In electric potential difference, charge flows from one end
to the other.
Ohm’s Law and electric potential difference
Ohm’s law shows the relationship among voltage, current, and
resistance.
Electric current is the flow of electric charge. Electric
resistance depends on the thickness and length of the wire, for thinner and
longer wires will offer more resistance. Electrical resistance is measured in
ohms Ω
A big question involving current and voltage is; why does a
flashlight get dimmer as the battery becomes weaker?
Answer: As a battery becomes weaker its voltage decreases,
and with less voltage there is less energy per electron meaning that the
current is stronger.
An example problem involving Ohms law is; calculate the
current in the 480 ohms filament of a light bulb connected to a 120 V line.
Current = 120/480
Current = ¼ Amps
Types of currents, sources of electrons, and power
The two types of currents we learned about in class were direct and alternating currents
In direct current, charges flow in one direction. In alternating
current electrons in the circuit are first moved in one direction then in the
opposite direction.
Although most people may not acknowledge it, but when one
flips the light switch on a wall they are completing the circuit thus allowing
electrons to flow through the current (current is established at the speed of
light note this is not the speed of electrons.
Two common misconceptions about electric energy is one: electrons move through the wires by electrons bumping into one another like dominos. This isn't true because throughout the entire closed circuit all electrons react simultaneously to the electric field. The second misconception about electric energy is the source of electrons. The source of electrons come from the conducting circuit material itself, they are not something you buy or something you get from electrical outlets.
Electric Power is the rate at which electric energy is converted into another form, such as mechanical energy, heat, or light.
Electric power = current x voltage --------> P = IV
Watts = Amperes x volts
The relationship between power and energy: Power = energy per unit of time
Energy = power x time
Parallel and Series Circuits
Series circuits: Wires are connected end-to-end forming a single path for electrons to flow. The total resistance to the current in the circuit is the sum of the individual resistances along the circuit path. The current is numerically equal tot he voltage supplied by the source divided by the total resistance of the circuit.
Here is what a series circuit looks like
Parallel circuits: Are connected to the same two points in the circuit, but the circuit branches of into separate pathways from point A to B as shown in the diagram. Because each device connects at the same two points the voltage is therefore the same across each device. As more branches are added current increases while resistance decreases.
Whenever overloading occurs in a circuit, there is more current than the wire can handle causing it to heat up and melt. To prevent the wire from melting and possibly causing a fire, fuses are used to connect the entire line that will melt if the wire gets too hot. When the fuse melts the circuit is disconnected thus sparing the wire.
What I found most difficult about what I have studies is answering the question; Why do light bulbs often blow when they are first turned on rather than after they have been on for several minutes?
The answer to this question is, because when the bulb is turned off the filament becomes cold. But once you turn it on the filament heats up pretty fast due to the current that has just begun to flow. Often the filaments aren't able to handle the increased amount of energy flowing through them causing them to burn out. But when light bulbs have been on for several minutes they have already equalized and the electrons are flowing at a constant pace.
I overcame this difficulty by doing some research online to learn more about what a filament is and why they burn out.
In this unit especially I had to ask more questions than usual, for it was the hardest unit for me to understand. I am not very good with understanding mechanical things; therefore, electricity and current weren't easy for me to understand. Looking for sources for my blog posts was also more difficult than usual, for I would read a website and not comprehend what it was exactly talking about, for there are numerous ways of explaining charges and electricity. By now I feel that I have a more clear understanding of the major terms we learned in this unit, and my effort outside of class is the reason why.
My goal for the next unit is to spend more time elaborating on my homework questions. Instead of writing simple answers I hope to give more detail into why I think my answer is correct.
