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FIRST OF ALL...

MERRY CHRISTMAS & HAPPY NEW YEAR

HAPPY HOLIDAYS

Hey guys! (and Mrs. Kozoriz!) Did you have a great winter break? I finally got this post up. I have been procrastinating on everything. I had so much time that I didn't know when to actually do this post. I didn't realize that we go back to school on Monday until today. Pretty sad... I hope everyone's all pumped up for the new year even though it means GOING BACK TO SCHOOL. No more sleeping in - BOOO!! I hope you guys are happy with all the presents you got from your loved ones. However, we should turn our switches back on to let the current flow in our circuits because guess what? MORE CIRCUITS when we get back! HAHAHA! Anyway...

DECEMBER 21, 2007 AGENDA:

We went over the `Simple Circuits` worksheet. I can't remember anything else that happened except for a few people decorating Mrs. Kozoriz's white board according to the aforementioned holiday of the year. Everyone was basically excited for the tantalizing two-week holiday. We were all excited to exit the doors, go home, hang out with friends, and finally be able to sleep in everyday! Of course, there are PRESENTS waiting to be opened.

Here are the answers for those who didn't take them down last year.


1.a)



b) Resistance_total = 10Ω + 10Ω + 10Ω = 30Ω (The Greek letter, Ω, represents OHMS, which is the unit for resistance.)

c)

(The unit for current, I, is A or amperes.)

d) Potential Drop = 0.4A x 10Ω = 4V (The unit for potential drop is volts, or V.)

e) Current = 12V / 30Ω = 0.4A

(Note that the total current circulating a SERIES CIRCUIT is the same as the current that goes through each of the resistor.)

f) Power = 4V x 0.4A = 1.6W (Watt is the unit for power.)

2.a) b)

c) Current_total = 12V / 3.3Ω = 3.6A

d) Potential Drop = 12 V (In a parallel circuit, each resistor has the same potential drop.)
e) Current in each resistor = 3.6A / 3 = 1.2A
f) Power = 1.2A x 12V = 14.4W



3) Series circuit = 2.4 watts; Parallel circuit = 11 watts


4.a) 1440Ω
b) 0.16A


REVIEW:

• Electric Potential - is the electric potential energy per unit of charge
• E = qV
• Electric Potential Difference (voltage) - ∆V

*** It is necessary to determine the total or equivalent resistance of the circuit before other elctrical quantities can be calculated. It is also important to identify the resistors that are in series with each other and those that are parallel with each other.

*** Add the resistors to reduce the number of resistors in the circuit. Begin by looking at the resistors furthest from the source (battery).

• Kirchoff's Current Law - the sum of the currents entering a junction must equal the sum of the currents leaving the same junction
• Kirchoff's Voltage Law - the sum of the potential drops around a circuit must euqal the sum of potential rises around the circuit
• Factors that affect resistance :

1. Length - the longer the conductor, the greater the resistance
2. Cross Sectional Area- the larger the cross sectional area, the less resistant it is to charge flow
3. Temperature - the greater the molecular motion, at higher temperatures, the greater the resistance (not for all substances)
4. Type of Material - some materials are better conductors than others.

• RESISTIVITY - general measure of the resistance of a substance, has units Ωm

- where R is the resistance in ohms, L is the length in meters, A is the cross-sectional area, in meters² and ρ is the resistivity in Ωm²/ m

• Five steps to follow to successfully analyze a compound circuit:

1. Each set of parallel conductors must be replaced by a single equivalent resistance
2. Each series resistance must be combined to find the total.
3. Total current in the circuit can be found using the equation: I = V / R
4. The voltage across each series group is found using: V = IR; to check, the total voltage must equal the sum of the individual voltage
5. The current in each branch of the parallel conductors can be found using: I = V / R; to check, the total current must equal the sum of individual currents

Oh and I remember now. We got more worksheets for this unit. Make sure you do them! Be careful because they are tricky. You can easily get confused and mix up the rules for series and parallel circuits. See you guys on January 7, 2008. Lastly, the next scribe is DINO!

HAPPY NEW YEAR TO ALL!

HAVE A GREAT 2008!!!