Unit 6 Blog Reflection

This unit focused mainly on electricity and the different components that make our electrically powered appliances work.

Some important terms to know:

Current - a current allows for the movement of charges. A current flows through every part of the circuit at the same time.

Conductor - conductors allow charges to flow freely

Insulator - insulators do not allow charges to move freely

The first concept we covered was the concept of charge and polarization. Positive charges are held in protons while negative charges are held in electrons. If an object has more electrons than protons, then it is negatively charged, and vice versa. It is important to know that like charges repel each other while opposite charges attract each other. There are 3 ways to charge an object:

1) Direct Contact

2) Friction

3) Induction

Direct contact is self-explanatory in that objects transfer charges by touching each other, leaving the objects with a net positive or negative charge.

Friction occurs by rubbing objects together. Electrons are “borrowed,” they move from one object to the other.

Induction is a bit different. In induction, there is no contact between the objects. There is a neutral object and another charged object comes very close to it. The like charges are repelled and the opposite charges are attracted to the charged object. This causes the neutral object to polarize, meaning its charges separate. The opposite charges are still attracted to the charged object while the like charges are repelled and find the easiest path to the ground, fleeing the once neutral object. This object is then charged.

Lightning is believed to be a product of induction. In a storm, the clouds are heavy and rub together. The friction causes the clouds to polarize with negative charges on the bottom and positive charges on the top. The strength of these charges causes the ground to polarize as well, with positive charges on the surface (because they are opposite and attracted to the negative charges) and negative charges deep into the ground. The attraction between the opposite charges of the bottom of the cloud and the surface of the ground is strong and the charges want to equalize. When enough energy can flow through the electric field created between the cloud and the earth, the charges equalize through the air. The lightning is the result of the release of this energy. Lightning rods work by providing the easiest path to the ground for the lightning to follow. The ground is positive and the lightning rod conducts the positive charges to the highest point so that the lightning is attracted to it.

Plastic wrap sticks to bowls because of induction as well. The wrap is negatively charged by friction and when brought near the bowl, the bowl polarizes. The positive charges in the bowl move close to the negative charges of the plastic while the negative charges of the bowl move away. The distance between the opposite attractive charges is smaller than the distance between the like repellant charges. Since there is a greater distance between the repulsive charges, the force between them is less than the force between the closer attractive forced because, according to Coulomb’s law, force is inversely proportional to distance squared so the smaller the distance the stronger the force and vice versa. Thus the plastic wrap sticks to the bowl because of the strong force between the attractive charges.

There is a problem similar to this one that involves a balloon sticking to the wall. The only difference really is that the balloon is first charged by friction. This problem is a big one!

Coulomb’s Law is also very important to this section. It states that the force between any two charges is inversely proportional to the distance.

F= k q1q2 / d^2

Note: it is very important to remember to square the distance!!

Along with charges and such we learned that dryer sheets are used to reduce or prevent static cling in your laundry. They coat the clothes so that friction does not charge them when they rub together in the dryer. This was a fun fact, in my opinion.

Next we learned about electric fields, which are the area around a charge that can influence another charge. We usually talk about electric fields in relation to positive charges and how they influence them.

The equation used to find the force of an electric field is: E = F / q (force per Coulomb)

Note: q is the symbol for charge or Coulombs in equations.

Electric fields are drawn with arrows pointing in the direction of force the field will have on a positive charge. This tells us whether the charge that the electric field is centered around is negative or positive- if it is positive, the arrows will point out, if it is negative, the arrows will be pointing in towards the center. The farther out the arrows are, the weaker the force that the field has on the positive charge is. The arrows themselves display this visually as they get more widespread the further from the center they get.

When an object is on the inside of an electric field in a way that it is not affected by outside charges and it has no net force on it because it is either pulled strongly by a few close charges or less strongly by a ton of distant charges, this is called electric shielding. When you are in a car during a thunderstorm, you do not get struck by lightning because the car acts as an electric shield.

Our next big topic was voltage. Voltage, or electric potential energy difference, is the difference in potential energy between two points. It is also a measure of how much energy we can get out of one Coulomb of charge. The larger the difference in charges, the larger the difference in potential energy and, consequently, the possible change in kinetic energy is greater.

Voltage equals the potential energy difference per Coulomb of charge.

V = ∆PE / q

As for units, voltage is measured in volts (big surprise), which are equal to Joules per Coulomb (energy per charge).

Ohm’s Law described the relationship between voltage and current by putting it into an equation with resistance. Resistance slows down the current and weakens it. The stronger the resistance, the weaker the current. The stronger the voltage, the stronger the current. Therefore, voltage and current are directly proportional because voltage is the source of current, while current and resistance are inversely proportional.

Current = voltage / resistance.

I = V/ R.

Current is measured in amperes, voltage is measured in volts, and resistance is measure in ohms. This equation can be rearranged to solve for any of the variables.

To add on to resistance:

Resistance can be increased by lengthening or making thinner the filament of the bulb that the current flows through. Also, resistance increases as temperature increases. This is why you are more likely to burst a bulb right when you turn a light on because as time goes on the resistance increases and the bulb gets hotter and dimmer. A high wattage bulb, however, will have a higher voltage thus a stronger current and less resistance. It will be brighter.

To wrap up the unit we learned about circuitry. Circuits are the pathways that currents flow through. The entire current flows at once through a circuit and will always take the path of least resistance. There are two types of currents that we learned about. The first, direct current (dc), is comprised of charges flowing in one direction. DC is always used in batteries. The other type, alternating current (ac), electrons move in one direction first and then in the opposite direction. This is done by alternating the polarity of the voltage causing the current at the voltage source. AC is typically used in commercial items and household currents are ac. A diode is a tiny electronic device that acts as a one-way valve to allow electron flow in one direction only. AC changes every half cycle so the current passes through the diode half of each period. The output here is a rough dc and it is off half of the time. Capacitors are used to maintain a continuous current and smooth out the bumps.

Capacitors are made up of two plates that store charge. They transfer electrons between each other for a while, taking time to build up a charge. They the release strong currents and have to build up again. An example of this is a camera flash- you have to wait between flashes because it takes the capacitors time to reload.

The net flow of electrons is referred to as drift velocity.

Electric power is the rate at which electric energy is converted into another form. The equation for power that we already knew is:

Power = energy / time.

The new equation that we use puts power into the context of current and voltage.

Power = current x voltage.

Just as there are ac and dc currents, there are different types of circuits that can be constructed. A series circuit has every appliance attached in the same current to the voltage source. A parallel circuit, however, splits the current between each appliance.

The more appliances that are added to series circuits, the greater the resistance. The current per appliance decreases so each appliance gets weaker/dimmer. Parallel circuits work in the opposite way. Each appliance that is added brings more current to the circuit. As more appliances are added, the current increases, the resistance decreases (it is halved as more appliances are added) and the voltage stays the same. In a series, if one light bulb is removed, none of the bulbs can work because the circuit has been broken. In parallel, appliances can be removed and the rest will work fine. All homes are wired with parallel circuits.

Fuses are made to protect circuits. They connect the circuit and current flows through them- when the current gets too strong and overheats, the fuse breaks and thus breaks the circuit so no more current can flow to the appliances. The fuse is attached to the series circuit with no problem and must be attached to the series part of the parallel circuit so that it controls the current to all appliances connected.

What I found difficult about what we studied in this unit was the concept of capacitors and the energy difference part of voltage. This really tripped me up but Mr. Rue re-explained both concepts in review sessions; hearing the information a second time and in a different way helped me to process it and return to the information, understanding it better the second time.

My effort towards quizzes in this unit really paid off and I am glad that I studied for all the quizzes this unit. Next unit, I hope to keep up with my daily homework better and be more consistent and thorough with homework assignments- it is easy to get caught up in other work and to rush through or to not finish the homework. I think I contributed to class heavily, just as I have been for the rest of the year. I do, however, need to work on explaining concepts concisely and clearly.

This unit connected heavily to my daily life because I use electricity all day and I never even knew how many natural physics processes occurred (even just by turning on a light). The most relevant and interesting thing for me was how light bulbs are lit and how circuits are constructed as it clarifies for me how my everyday appliances are working and how they are powered.

(This unit we did not have time for a podcast, but next maybe time!)