Exam 2

There WILL be class tomorrow(Wednesday). There will also probably be a quiz. (Think applications of guass' law or intro to capacitance or both!) We will be talking about capacitance and finishing most of chapter 24.

The exam is graded. I was pretty happy with the result. There were more A's this time then on the first exam. However, the average went down somewhat. Several of you brought your grades up substantially!

See you all in class,
mmason

homework

So what's going on with the homework? Was it still due at 12?

About the solution given yesterday in SI....

there's some mistakes been pointed out....

and milan wants me to write nothing more than this....

so here are the solutions

http://docs.google.com/Doc?id=dhtfdzv3_5hbrhsjhm
img18 page1

http://docs.google.com/Doc?id=dhtfdzv3_7ctpg6whk
img19 page2


Milan's practice exam solution

and they are here.

http://docs.google.com/Doc?id=dhtfdzv3_13dgm2r3f7&hl=en
img25 page1

http://docs.google.com/Doc?id=dhtfdzv3_11hdw6qjfx&hl=en
img24 page2

http://docs.google.com/Doc?id=dhtfdzv3_9dxbmcrdq&hl=en
img23 page3

http://docs.google.com/Doc?id=dhtfdzv3_21drc83zhd&hl=en
img22 page4

http://docs.google.com/Doc?id=dhtfdzv3_19f8967ggq&hl=en
img21 page5

http://docs.google.com/Doc?id=dhtfdzv3_17f9qddpd6&hl=en
img20 page6

and these are the handout for ch.21 & ch22

http://docs.google.com/Doc?id=dhtfdzv3_23c64x6md4&hl=en
img26 page1

http://docs.google.com/Doc?id=dhtfdzv3_25dgm2wchk&hl=en
img27 page2

http://docs.google.com/Doc?id=dhtfdzv3_27x28sqx8r&hl=en
img28 page3

IMPORTANT!!!!!! Si Study section for Exam 2 on Sat 11/1/08

mimi said:

Hey, guysThere is a special SI session for Mason's 4B class
on Saturday 11/1/08, and I do have a lot of stuff to share with you
guys, and they might help for u for preparing the second
exam! And i also have some interesting probs for those ppl
who are ready for the exam!please feel free to come~~
Place: study room~~hopefully i can get a classroom
Time: 1 pm - whenever u are ready for the examHave fun
on physicsHappy halloween : )cya on Sat

mimi

Circuits Notes

Here are the notes on Circuits

http://docs.google.com/Doc?id=d3w6sww_705hjfgjvhs

Have fun!
mmason

DC current: Resistors, and Introduction to Kirchhoff's Law

on wed. October 22, class started with a fiesta of knowledge just like all Wednesdays.

In the fiesta of knowledge we were asked to find the resistance and resistivity of a copper extension cord, the max current through a copper wire and some other stuff that I do not remember.

After the fiesta we started unit 7: Direct current circuits,we skipped the first couple sections.

we started on 7.7 Using a multimeter

we built a circuit with a resistor and were given a multimeter.

We learned how to use the multimeter to measure measure DC current(amps), potential difference (volts) and resistance and this is how is done for the multimeter we were using:

1)To measure DC current the selector on the multimeter has to be on Amps, the correct range, connected in series with the circuit element and the positive test lead in the amps receptacle.

2)To measure potential difference(volts) the selector has to be in volts, correct range, connected parallel to the circuit element, and the positive test lead in the volts receptacle.

3)To measure resistance(ohms) the selector has to be on ohms, correct range, the resistor has to be disconnected from the battery, and the positive test lead in the resistance receptacle.

the negative test lead stays at the same position on the negative charge receptacle for this multimeter.

Then we moved on to Electric Power

we found out that if you multiply voltage (Joules/coulombs) and current (coulombs/seconds) the coulombs cancel and we end up with Joules/seconds which are the units for power. so, we get the definition of power:

P=VI (power=voltage X current

Resistance and its measurement

In a circuit potential energy is lost due to resistance. one of the most common resistors is the light bulb which turns potential energy into heat and light. But most electric circuits use resistors made of carbon, known as graphite, for resistance. Carbon is used because its resistance does not vary with the current passing trough them. They are cheap make and and can be made with low or high resistances.

Carbon resistors are color coded with different color bands that tell us its value in ohms. To get the value of the resistor we use the following table:

The Resistor code Table

Black =0

Brown =1

Red =2

Orange=3

Yellow =4

Green =5

Blue =6

Violet =7

Gray =8

White =9

silver =(+/-) 10%

gold =(+/-) 5%

so this is how we use the table to get the value of a resistor

value of the resistor (ohms)= AB x 10^C (+/-)D

Gold, and silver bands represent the tolerance of the resistors(if your first line is gold or silver turn the resistor around you are reading it backwards).

once you is turned around the fist two color band are A and B.(do not multiply A and B)

A and B are just placed next to each other and that is the first number.

the third color line is the exponent C, and finally the fourth line is you tolerance, D.

Prof. Mason gave a 2 resistors and we calculated their resistance using the Resistance Value Table, the we did the same for some combinations he wrote on the board. Then he proceeded to show what happens when a resistor is subjected to a higher current that what is rated for. Using a generator he burned a poor defenseless resistor to a crisp.

Measuring Resistances in Series and Parallel

We were given two identical resistor and then three identical resistor using a multimeter we measured the resistance in parallel and in series and we found that resistors in series in parallel the voltage stays the same but the two currents add up to the total current.

When we put the resistors in parallel the current stays the same voltages coming from the two resistor in parallel add to the total voltage of circuit

so this are the formulas:

Resistors in Parallel:

1/Req=(1/R1)+(1/R2)+(1/R3)+..........

Resistors in Series:

Req=R1+R2+R3+............

We also found that we have circuit with two resistors in parallel we can find the equivalent resistor using these formulas and then replace it with a single resistor.

Introduction to Kirchhoff 's Laws

First law: Junction Rule(based on charge conservation)

The sum of all the current entering any node or branch point of a circuit entering any node or branch point of a circuit must equal the sum of all currents leaving the node.

Second law: The Loop Law (based on energy conservation)

Around any closed loop in circuit, the sum of all emfs, voltage gains provided by batteries or other power sources, and all potential drops across resistor and other circuit elements must equal zero.

------------------------------------------------------------------------------------------------

we stopped because the class ended I agree with professor Mason this class is to short. Thursday, Friday, Saturday, and Sunday, four days without going to class is too much.

P.S I missed some of the stuff we did right after brake because Dante and Joy were holding up the line at the Mountie grill. It took them 25 minutes to order water and a cookie.

BAM!! + BAM! = 2BAM!

Jesus

Monday, Oct 20th, 2008

Hmm...... My first blog and I don't remember much lol

orz... I have no idea where to start but I'll give it a shot

So, the first question(?) we did in class was the empty cageish(?)

barrel that was electrically charged and aluminum foil was

hung inside the cage, and out side of the cage.

Our task was to guess how these foils reacted when the cage

became charged.

The inner ones did not get affected because the electric field

inside a conducting substance cancels out, and only the outside

ones flipped towards the outside. ( I aint rly sure if this is useful)

The second part(!) was ...... rolling balls down the nailed board(?)

The factors that affected the time the balls took to fall out was

1. The Cross sectional Area ( same as a wire, R = inversily proportional)

2. The Length of the run ( same as a wire, R = directly proportional to length)

3. The Density of the nails ( for sitting, the denser the better, but...... for

- the balls, less denser -> faster time )

The 3rd part was the...... relativity of parallel structure, series structure

of the batteries, and the light bulbs.

When light bulbs were set in a parellel structure, every lightbulb lit up

with the same brightness of a single bulb.

But when the light bulbs were set in a series structure, the brightness

decreased as more bulbs were added to the circuit.

When the batteries were set in a parallel structure, the voltage

equaled to a single battery, but the lifttime of the battery increased.

V = v1 + v2 + v3 ................for series structure

V = v1 = v2 = v3................ for parallel structure

R = r1 + r2 + r3................. for series structure

1/R = 1/r1 + 1/r2 + 1/r3 ..... for parallel structure

AND V = IR -> OHM's Law(?)

V -> voltage
I -> current
R -> resistance

Basically thats all I remember... for more detail,

go ask the professor maybe?