Fin - Let's Hope We All Didn't...

Sample Final Exam

For those people that can't stop by Prof. Mason's office to get the sample exam...
here is the scan of it...
have fun study it this weekend~ :)

click it to see the bigger version

Photoresistors!! 5-11-09

Hey Guys-

On Monday we learned about photoresistors and had a robot day! Photoresistors are light sensitive resistors whose resistance decreases with the amount of light falling on them.

We will be using photoresistors on our robots for the "Follow the line" competition and for "Robot Sumo."

We've all seen photoresisitors somewhere in our lives.....for instance my car as an auto setting for my headlights to turn on and off. When the resistor has enough light falling onto it, it causes electrons to jump into the next conduction band. The resulting free electron conduct electriciy, and therefore low the resistance of the resistor.

To use this on our robots, we needed to figure out the resistance range of the resistor for different light intensities. We used the 'white' of the our white boards and the black of non reflective electrical tape.

Once this is figured out, interface the resistors using voltage dividers to your microprocessor. The photoresistors will control one or both of your motors. You'll want to think about how you want your robotto behave for the line following competition and also think about what you want your robot to do when it faces the white outline of the sumo ring.

Oh...Mason also did some cool stuff in class...no he didn't light either of the Peter's on fire, but he put stuff in a microwave that shouldn't have gone into it, and made sparks fly.

LRC Circuits - 5/6/09

Today in class we had lots of fun with oscilloscopes and LRC circuits. If you haven't looked at Mason's AC circuits notes, I highly suggest you do or you might internally combust due to massive confusion. Mason's notes really helped me understand the vector problems in the HW.

We took a good look at phase angles and how to caluclate them and what they mean. Basically when looking at both current and voltage in an oscilloscope, current and voltage will both oscillate sinusoidally but not at the same time. The difference in which the current leads or lags the voltage is called the phase angle.

Phase angle (phi) = tan(-1)(XL-XC)/R = 2pi*delta t/T(dr)

Where T(dr) = the period of oscillcation of the driving emf.

Since it has been almost 10 years since I had to figure out the period of a function, I spent the entire class asking myself WTF? So it also might be really useful to know how to find the period;

Period(T) = 1/f
w=2*pi*f

We briefly went over the Root Mean Square Current and Voltage. Mason proved that the average current and voltage on always equal to zero, but the average power of the AC circuit is not equal to zero....ya we've all been zapped by AC circuit.

In general, your equations of Voltage and Current will look something like this for a LRC AC circuit in series;

If circuit is voltage diriven;

V(f)= Vmax*sin(wt)
I(f)= Imax*sin(wt-phi)
phi = phase angle

If circuit is current driven.

I(f)= Imax*sin(wt)
V(f)= Vmax*sin(wt-phi)

The circuit will still obey Kirchoff's rules.

Good luck on all of the H-dub!!

AC Circuits Notes

The notes are available here:
http://docs.google.com/Doc?id=d3w6sww_1142spch8thj

STRIKE #3

Speaking of Monday, Mason wasn't here on Monday, but Peter, Me, Brandon, Chris Z., and quite a few others were there doing a little work on our robots. Well, Peter wasn't working on any robots, but he did do his SI session. :3

We took our tests last Monday, right? So... extra credit? XD

Wednesday April 22, 2009

Today was a relatively relaxed day in class. Since we haven't had a robot day, or even a robot half day, in a long while we dedicated the entire day to building robots. We didn't get to augment our toys with weapons yet but we did add some motors to the circuit. A mobile sentry is better than a fixed one right? We began by breaking up into individual tasks. The first task was to solder wires to the motor. The second task was reminiscent of our lego years in that one person must build the drivetrain. The final task was to attach the relay and transistor circuitry to the protoboard so the motors can be controlled in on/off (transistor) and forward/reverse (relay). Once all three tasks were completed they were to be joined together and tested for error. Not many groups got this far so it will be completed on monday after the test. The homework consisted of a practice test of problems from last years test, homework problems and freshly made problems. It was a relatively easy day to make up for the brutal one we shall have on monday. Good luck to everyone!

More magnets and electricity! Hey at least nothing was melted...

Hello everyone. This is my first ever blog post - that's right, first ever! I've never thought that my first ever blog post will be about physics but hey, you can't predict everything, right? I apoligize if the writing is bad/boring because afterall, I have never done a blog post until now!

So here it goes!

We started off first by getting the news that our last homework involved with chapter 28 instead of 27 only. Wait a minute, I thought that homework was on chapter 27 only. I guess that's why I did terrible on a couple questions (or maybe it was just me not realize that? Jeez...).

We then did experiements about Faraday's Law which involving wire loops and magnetic field. We found out that the more loops there are in the coil, the stronger the magnetic field of the coil is. Based on the results, we found out that the magnetic field of the coil is proportional to the current flowing through the wire and the number of loops there are in the coil.

We then learned about electromotive force, or emf. emf is from the potential difference generated magnetically. It's effected by the area, the number of loops, and rate which magnetic field changes (velocity) of the coil.

One thing that caught my interest at the end of the class was that Mason and Peter tried to demostrated something that reminded me about a phenomenon called Maglev, or magnetic levitation. This tech is used quite frequently in Japan's train system. Now, I don't know the exact detail of the system or the relationship between those two, so maybe professor Mason can explain a little bit about this? I know it's offtopic but I still find it rather interesting.

That's all folks! I hope you are still awake at this point after reading through all that! Celebration (?) is next monday so hopefully everyone is getting ready for it!

PS. Nerf offshore flow please. 100 degree weather in April is ridiculous 囧rz.

Wednesday April 8th, 2009

Class is cancelled yet again. Sign in sheet is on the southernmost door. Early weekend!!!

Working with Transistor

In today’s lecture, we learned the new device named transistor which is act like an ON/OFF switch. The transistor can be made of either “N-P-N” or “P-N-P” form. It has three legs, a gate (connected to ground), a collector (high potential), and an emitter (low potential). When a small current flow into the gate as key opens the door, main current can get through from the collector to emitter, increasing as linear function. However, the main current will maintain same value if the gate current reaches some certain value. After learned the properties of transistor, we designed a circuit controlled by it. A LED and a fan were turned on/off in some time intervals determined by program. The advantage of using the transistor is: we can design a circuit with two power supplies, one for “brain” (run by a small battery) and one for body (mechanical part, run by large battery), to avoid wasting power.

transistor notes

Here are today's notes:
http://docs.google.com/Doc?id=d3w6sww_1138ctrmd3hh

4/1 homework

anyone else notice that todays homework is due tonight at midnight? is this a type-O or do i need to stress myself out and do it tonight?
any thoughts?

Monday March 30, 2009.

For all of our hard work Mason has granted us a day off from class. Even though it's on account of jury duty we still thank him for a four day weekend. The timing seems really convenient but we won't poke holes at it. Thank you professor Mason!

We should be covering Gauss's law (Chapter 22) on Wednesday for those who want to get ahead.

Answers to my practice test

Answers for practice Celebration

Day 8 March 18

Today we did section 6.1-6.5 on our handout. For the first part of class we started off by solving some problems on the motion of an electron in a uniform electric field. we learned how an electric field affects the motion of an electron with an initial velocity and that E-field causes the deflection of the electron in the oposite direction of E. we did some calculations on our white boards to prove that the deflection is proportional to voltage.. and by using these equations:
F=ma
F=qV/d
and 2D- kinematics equations for the trajectory of the electron we were able to solve for d, and we realized that the deflection is proportional to Voltage(the higher the voltage the greater the deflection). we needed this information in order to understand the second part of class, which delt with function Generators and Oscilloscopes.
For the second part of class we played around with a function Generator, also called (wave generator) which is a device that can produce different voltages in a regular pattern. we connected a speaker to the wave Generator and we played around with different dials and bottons on it and we noticed the sound changes: 1) changing the frequency changes the pitch of the sound. 2) changing(increasing) the amplitude makes the sound louder . 3) changing the function(sine, triangle or square) changes the timbre of the sound coming out of the speaker. After that we learned how to use an Oscilloscope and we connected in to the function Generator and noticed how changing the frequency and amplitude changes the graph(motion of electron)displayed on the screen of the Oscilloscope. we also learned how to calculate the period by just looking at the graph.
for the last part of lab we built capacitive filter cicuits on our breadbord, and we conected it to the Oscilloscope and the function generator. then we collected data for the changes in amplitude and voltage when we change the input frequency. then we graphed the data we got using loger-pro. and we noticed the constant votage drop in the first circuit(capacitor and resister), and the constant voltage in the second circuit(two resisters).
GOOD LUCK ON THE EXAM!
O MY BAD, (CELEBRATION OF KNOWLEDGE!)

Practice test for celebration 1

This is a practice test that I made up. There was no input from Prof Mason on any of these questions, but I thought these were fairly challenging and would pose a good exercise. Prof Mason said he would be handing out his practice celebration on Monday.

Peter's Practice Test

The answers for my practice test will be posted Monday night. I will attempt to have the answers for Masons up on Tuesday night or Wednesday morning. Good luck with studying =)

Edit** For problem one, there is a positive test charge at the point where you need to find the force and electric field.
Problem two, it should be surface charge, not linear

Day 6 March 11, 2009

The first thing we did in the class was a quiz. The quiz is about using the Kirchhoff's Rules to find current in the circuit. Then using the current to find the voltage and the power to compute the total power.

Generally, we use the sum of current and voltage in a loop are both equal to zero to find the current. First, The junction rule I1=I2+I3 will setup the first formula, and the loop rule will create the other two formulas. Then, we can do some algebra for the unknowns in the formulas to find the current. After that, V = IR can be used to find the voltage by current and resistant. Finally, use P = IV to get the power of each resistor, and add them up to get the total power.

I did the questions wrongly, but I found my mistakes soon. All loops have to in the SAME direction. It was a good quiz because I even did not find I was doing something wrong in the homework!


The second part in class was slightly different with the class. We were learning something which is not in the book! The robot project was started! Before touching the hardware, we had to learn some theory for that.

What we learned in this part was the protocol for the devices to communicate. We learn how it works. It translate ASCII code(American Standard Code for Information Interchange), which is commonly used in computer system to represent characters and to some digital signals. The character in ASCII code first translates to 0 and 1, then it reverses the order of the code then translates to positive voltage for 1 and positive voltage for 0.


The third part was doing some labs. We use a voltage divider, a potentiometer to build a bridge circuit to measure the temperature. We take the voltage in the freezing and melting point, which are already known as 100 and 0 degree Celsius, to calculate the room and the body temperature. From the result, we will get a line which show that they are in linear function.

An interesting thing in the lab is that we found this device is really sensitive. It could even catch the temperature change caused by our human body moved away for a few centimeters!

Solving circuits with matrices

Here are the instructions for solving simultaneous equations with your calculator. Note, these directions are for the TI 83 + only. If you have a different model, your procedures will be different.

http://docs.google.com/fileview?id=F.f9c99189-1d8a-4dce-8ad0-9bd68b62ef01

Hmm

Better Be Right Or Your Great Big Venture Goes West

Here's one that's PC, kosher, etc.

SI times are set for the rest of the semester. I have no intention of changing them anymore. Hope to see all there!

Day 5 Physics 4B March 9, 2009

Really long recap:

Some important announcements were made before class today. First of all Peter set a new SI session date. His new session will be on Friday from 10:00am-12:00pm. I cannot confirm this as a static date/time so you’ll have to prod him for more information whether it will change or not. His other sessions that are an hour before class will remain the same for all your last minute homework needs. Incase you didn’t know an hour before class is 11:00am-12:00pm (class starts at 12:00pm). That brings me to the next announcement. BE ON TIME! The more you guys are late the more often we have quizzes. I don’t know whose idea it was to reward the people that are on time with quizzes but something seems quite off with the logic.

In class today was more of a problem solving day with some hands on but not quite as much as the previous week. We covered sections 4.5 to 4.13.1e in the packet in the seamlessly short 220 minutes we have together; although most of us didn’t get even close to part E so we should be continuing it on Wednesday. The first lab we worked on involved comparing which resistor gets hotter (spoiler: the one that causes more pain gets hotter). The purpose of this was to see whether more or less resistance causes more or less heat respectively. The answers may not surprise you. To prove this Mason hypothesized it would be less painful to light a 5 ohm resistor on fire than to hold it. After a lot of waiting and smoke the flames never emerged and we were all disappointed with Masons promises not delivered. With the lesson of not lighting resistors on fire learned , or in my case “try this at home until we get results”, we next learned how to identify the resistance of a resistor by the color coding on the resistor itself. There are some easy rhymes to remember the BBROWGBVGW that can be found with Google but posting there here might be frowned upon for not being PC (about 80% contain rape for red and it only goes downhill from there). After practicing the codes for a while we moved onto the meat of the day; Resistors in series and parallel calculations by either brute force or Kirchoffs Law. I will make the lessons learned from these at the end of the blog in an easy access location. This part of the day dragged on endlessly for what seemed like eleventeen hours. But when it was all said and done I shall, along with many others, be harassing Peter for help on Friday about Kirchoffs law (since when was a law ever easy to understand). In our curiosity about the 5 ohm resistor that was “lit on fire” we decided to test the change in its resistance after being exposed to high heat. There was a minimal change in resistance as recorded by the multimeter. Those lil’ guys are Tonka tough.

Notes:

One of the more interesting things we did as a quick refresher was we wrote V, I, Resistance and P in terms of SI units. They turned out to be:

-V = ( Kg * m^2 ) / ( s^2 * C )

-I = C / s

-Resistance = ( Kg * m^2 ) / s

-P = ( Kg * m^2 ) / s^3

Some handy notes for series/parallel resistors were:

-In series the voltages will add together but the currents will always be the same.

-In parallel the voltages will always be the same but the currents will add together.

-Add the resistances together for total sum in a series: R1+R2+R# =Rtotal

-For parallel multiply the resistance of each resistor then divide by the sum of all the resistors: (R1*R2*R#)/(R1+R2+R#)=Rtotal

Kirchoffs Law:

-The algebraic sum of currents into any junction must be equal to zero.

-The algebraic sum of the potential differences will also total out to zero.

-As long as proper signs are used Algebra or matrices can be used to solve these problems relatively easily.

-Page 888 of the book has more details on this (what a conveniently easy number to remember).

Fun things:

-On March 9 1934 Yuri Gagorin was born. He was the first man to go into space. (closest fun fact related to Physics I could find for March 9). On the plus side if you look at his picture on Wikipedia he has more medals than Michael Phelps.

-As an apology for such a sad fun fact here’s an awesome Physics related game to play when you’re bored… but not bored in class… unless you’re Mason… or Peter…

http://www.fantasticcontraption.com

Whenever you finish a level go look at some of the other ones people have created. They make you feel really bad for not being that clever.

In summary:

Read sections 26.1 and 26.2 of the book as well as 4.8 in the packet to recap everything we did today.

**no Peters were harmed during the learning of this class... sadly.**