Unit 7 Reflection

Unit 7 was all about electricity. The first things we had to get straight was positive a negative charges and the ways in which they work. Important things to know are that the positive charges are called protons, and the negative charges are called electrons. Opposite charges attract each other and like charges repel each. Usually when charges move they are electrons, because they are freer to move due to the fact that they are not bound to the nucleus like protons. Lastly, similar to the conservation of matter, electric charge can neither be created nor destroyed.

Now we can learn about Coloumb’s Law, which is  F=k(q₁q₂)/d². Which shows that electrical force decreases inversely as the square of distance between charged bodies.

Since we’ve got that out of the way we can talk about conductors, semiconductors, insulators, and superconductors.

1.     Conductors: Any material having free charged particles that easily flow through it when an electric force acts on them.

2.     Insulator: A material without free charged particles and through which charges do not easily flow.

3.     Semiconductor: Properties of a conductor and insulator; resistance can be affected by adding impurities.

4.     Superconductor: A material that is a perfect conductor, with zero resistance to the flow of charge.

There are multiple ways to charge an object, or transfer charges form one to another.

1.     By contact or friction:  Transfer by rubbing or simply touching.

2.     Induction: Redistribution of electric charges in and on objects by the electric influence of a charged object close but not by contact. For example, this is how lightning is caused.

           

Negative charges in the clouds cause the negative charges in the neutrally charged ground to move away leaving only positive charges at the surface. The ground becomes electrically polarized, which means that like charges are aligned with each other.

Since opposite charges attract, electricity runs to the ground. This is lightning.

Next up are electric fields, which one can see an illustration of above. An electric force per unit charge, and the inverse-square law can be applied to it.

The equation for an electric field is; electric field= F/q.

When dealing with electric fields there is something called electric potential, which is often called voltage. This is the electric potential per unit charge. To find voltage you use the equation, voltage= electric potential energy/ charge.  The electric potential in the equation is the energy a charged object possesses by virtue of its location. This all relates to the flow of electric charges, also known as current, and here’s how. In order for current to flow or charges to flow from on place to another there must first be an electric potential difference. So object A and object B must have differing electric potentials in order to start the whole process. When dealing with current there is something known as resistance (measured in ohms). Electric resistance is the property of a material that resists electric current. Ways to increase resistance are:

·      Thickness

·      Length

·      Temperature

·      Material

Now that we’ve learned that we can move on to finding the current in a circuit. The equation to find this is known as Ohm’s Law, which can be written as current=voltage/resistance (the unit of measurement is amps).

There are two types of currents:

1.     Direct current (dc): electrically charged particles flow in one direction. This type of current is used in batteries.

2.     Alternating current (ac): electrically charged particles that repeatedly reverse directions, or vibrate. Used in homes and mostly everything else besides batteries.

Current and voltage can be used to find electric power, which is the rate of energy transfer, or the rate of doing work. Power=current x voltage.

Lastly, there are two types of circuits, series and parallel.  A series circuit is an electrical circuit in which the devices are connected along a single wire such that the same electrical current exists in all of them. However, in a series circuit when one of the devices are disconnected they all go off. Also, as more devices are added the resistance increases, therefore reducing the current. Parallel circuits are electrical circuits that are connected in such a way that the same voltage acts across each one, and any single one completes the circuit independently. So, when one device is disconnected the others stay on, which is why this type of circuiting is used in households. When one appliance goes out the others will stay on. Fuses are used in homes to protect appliances. They control the flow of current and are connected to the parallel circuits in a series. When too much current gets to the fuse it blows, causing the whole system to shut off, saving your appliances from too much current that could cause damage.

Reflection:

 Some things I found difficult in this unit was the concept of an electrical field. At first, it was hard for me to get a grasp of what exactly they were. But, after being shown some illustrations I finally got a hold on it. Until we then brought in the ideas of electric potential and electric potential energy, which I have no idea why scientist would give them the same names. After, I finally got that straight I was fine for the rest of the unit. When doing the calculations, I learned how to manipulate the equation for Ohm’s Law or current = voltage/resistance so that I could find the voltage or resistance, when given the current. Then using this to find the power, which equals current x voltage. As I showed many examples of this unit relates completely to real life situations.