The Last Post

Today we learned about electrical power, and got some formulas:

P=VI,   P = V^2 / R,   and P = I^2 / R

The SI unit for Power is Watts.

We also learned about power rating, and how to read an electric meter.

We also got steps to find electrical cost:

• Find power and convert to kW
• find hours
• multiply time by power
• multiply by rate.

Electrical sefety

We learned:

• all voltages are dangerous
• AC is more dangerous than DC
• Electrical shock is a jarring shaking sensations that can cause burns.

Ohm's Law

    In Tuesday's class we reviewed electrical resistance. This determines how much current is drawn from an electrical energy source when an appliance is "plugged in."
   Resistance depends on the conductor within it. Resistance of a conductor depends on these four things:

• Length- the more length, the more resistance
• Thickness- thick wire provides less resistance
• Temperature- Higher temperatures lead to higher resistance. Super-conductors have a resistance of near zero when in extremely low temperatures.
• Nature of the Material- different substances provide different resistances.

After this brief review, we went on to learn Ohm's Law

Ohm's Law states that V=IR

• If the voltage is constant, an increase in current (I) must be the result of a decrease of resistance.
• If the resistance is constant, an increase in voltage results in a directly proportional increase in current.

     Current generally depends on the voltage and the resistance. However, note that Ohm's Law only works for Ohmic materials. (We won't work be working with any Non-Ohmic materials.)

The total resistance for resistors in series is equal to the sum of each individual resistor.

RS = R1 + R2 + R3 + R4 + __ + Rn

The total resistance for resistors in parallel is a reciprocal relationship.

1  =  1  + 1   + ...... + 1 
RP      R1    R2                   Rn

As more resistors are added, the total resistance will become less, thus increasing the voltage.


1.) If a battery maintains a potential difference of 65 Volts across a circuit and a current of 5.0 A flows through it, what is the resistance?

V = 65                       V = IR
 I = 5.0                      R = V  = 65  = 13 Ohm's of resistance
R = ?                                 I     5.0


We concluded the class by going over several examples.

Wednesday's Class

We spent all of Wednesday's class working on practice problems from the text book.
The assignment was:

• Pg. 649 # 1-6
• Pg. 653 # 1-2
• Pg. 655 # 1-2
• Pg. 659 # 1-5
• Pg. 673 # 21 a-e

Brady will post next

Kirchoff and Resistance

In Monday's class  we started by watching Krystle's Prezi presentation and then reviewing what was learned on Friday.
We then started to learn Kirchoff's Current Law which states that:

1. The current is conserved in a series circuit  I1=I2=I3=IT
   2. The total current in a parallel circuit is the sum of the current through each resistor connected in parallel.  I1+I2+I3=IT
   We also learned Kirchoff's Voltage Law which states:
   
   1. In a series circuit the total voltage is the sum of the potential difference across each individual resistor   V1+V2+V3=VT
   2. In a parallel circuit the voltage is conserved and the potential drop across each resistor in parallel is equal to the total voltage. V1=V2=V3=VT  
   In this class we also started to learn about Electrical Resistance which affects the amount of current drawn from and electrical energy source.

          The resistance of an appliance depends on the conductor within it and the resistance of the conductor depends on these four things:

1. Length- more length=more resitance
2. Thickness- a thicker wire has less resistance than a skinnier wire
3. Temperature-hot=more resistance cool=less resitance
4. Nature of the Material- different substances provide different resistances

         Finally we learned the formula to calculate resistance

          R=p(L/A)                   R= Resistance

                                                      p= Resistivity
                                                      L=Length
                                                     A=Area

Next is Brittany

Electric Circuits

We started Friday's class by watching the remaining Prezi presentations, and reading about outlets. Following the reading, we started a section on electric circuits.
Electricity Terminology:

• Electromotive Force (e.m.f) - the potential difference at a power source when no current is being drawn. The e.m.f of a regular "plug-in" is 110V. 
• Battery- a group of two or more cells. One cell is like a "AAA battery."
• Series Combination- when cells are connected with the positive terminal connected to the negative terminal. The electromotive force ( or voltage) is the sum of each cells. 
• Parallel Combination- all the negative terminals are joined together and so are the positive. 

Electric Circuits:

• A circuit always has an energy source (battery), an electrical appliance (bulb), a controlling device ( switch), and a protective device (fuse). The fuse is typically not included in the diagram. 
• Series Circuit- The electrons only have one path to travel. The circuit diagram above is a series circuit. 
• Parallel Circuit- there is two or more paths that the electricity can take. 

We finished the class by looking at Kirchoff's Circuit Analysis.

Kirchoff's Current Law 

• 1. The current is conserved in a series circuit. It is the same throughout the circuit. 

Shelby is next! 

Electric Current and Electric Potential Energy

• In Fridays class we learned of electric fields and how to calculate the intensity of it using the formula:

E=F/Q; where E=electric field intensity (N/C); F=electrostatic force (N); Q=charge(C)

• To finish off the class we compared electric current to the flow of water through a hose.  The two types of current are:

-Alternating Current (AC) which is current that periodically changes direction

-Direct Current (DC) where all the current is in one direction

 

• In Mondays class we learned the concept of electric potential energy.
• To summarize we can say that opposite charges attract and similar charges repel.

We then moved onto electric potential difference which is more commonly known as voltage.  It is the amount of energy needed to move a charged particle from one point to another.  We can calculate voltage with the formula:

                                                         V=W/Q

Where; V=potential difference (volts)

            W=work(J)

            Q=charge(C)

• To finish off Monday's class we learned of electrical grounding.  The point of a grounding wire is to carry excess charge away from the appliances and people and into the ground which has a charge of zero.

Next is Indianna

Electric Field

In todays class we learned about an electric field.


An electric field is a region in space where a force is exerted on a positive test charge.  It is a region that would cause a test charge to move if it were placed within the region.

Electric Lines of Force- lines that represent the direction that a freely moving positive test charge will move in an electric field.  These lines originate at positively charged objects and terminate at negatively charged objects.


The strength of on electric field is shown by the distance between field lines.  The filed is stronger when the lines are closer together.

The field lines want to be as far part as possible from each other.  When the charge is negative the field lines will point towards it and positive they will point away format he charge.

1st ~ B < A

2nd~ C < D

3rd~ G < E < F

4th~ J < H < I

We determine this by the number of field lines coming off or going to the charges.

Next is Kurtis

Electricity and Coulomb's Law

Today in class we talked about how Coulomb's are the SI unit of a charge.

1 C= 6.24 x10^18 Electrons   1 Electron= 1.60 x10^-19

So the charge of one electron is called the Elementary charge. This charge is also the charge of 1 proton.

To find the charge on an object we use the formula  Q = Ne 
                                                                              Q= the quantity of charge
                                                                              N= number of elementary charge
                                                                              e=  the elementary charge (always 1.60 x10 ^-19

Ex.    Calculate the charge on a metal-leaf electroscope that has an excess of 5.0 x10^10 electrons.

Q= ?                                                                   Q= Ne
N= 5.0 x10^10                                                   Q= 5.0 x10^10 (1.60 x10^-9)
e= 1.60 x10^-9                                                   Q= -8.0 x10^-9C


Coulomb's Law


This is the formula which is applied to find the magnitude of the force of repulsion or attraction between two charges.
                                                                          F=K q1q2
                                                                                   d^2


F= electrostatic force
q= charge (C)
d= distance (m)
k= 8.99 x10^9Nm^2/C^2 (always)

A negative force implies an attractive force.
A positive force implies a repelling force.

krystle is next