Make-Up Prototyping Lab 4/23/2014

Prof Mason couldn't making it to class today so we used the time as Lab to finish up our unfinished Breadboard Lab from last week...

We first finished setting up the circuit on the breadboard by using a potentiometer as Resistor #2 and adjusted it until its resistance was roughly about 2.15 kΩ.  We tried our best for this value since the potentiometer was too sensitive to adjust to an exact value of  2.00 kΩ.

The potentiometer (wiper-like element) is essentially a voltage divider for measuring electric potential

We then measured the resistance across resistors R_1, R_2, R_3, the potential differences (voltage), and currents i_1, i_2, and i_3. The data is as follows:

As the measured data shown above, the percentage discrepancy was extremely large as high as 130% for the third resistor.  Based on this observation, we conclude that the huge source of error is in the potentiometer due to the extreme sensitivity & difficulty to adjust.

Next, we ran the experiment again, except this time, we swapped the potentiometer with a resistor that had a measured resistance of 2.13 kΩ in beige-tan..

According to the new measurements, we can see that values were much more accurate than the previous attempt. Though better accuracy, however, the resistors still did not match the theoretical resistances that we had used to calculate the theoretical currents. We conclude the largest sources of uncertainty were in the resistors and the battery.  For instance, the battery alone provided 1.45 V instead of 1.50 V. The percentage discrepancy is still as high as 8.7%

Capacitors 4/21/2014

Got bummed by a surprise fiesta wahhh?!!?.... -__-"

Today it is about capacitors.  While the word capacitors may be intimidating, it basically is a device that stores charge similar to a battery.  It consists of parallel material that are tightly layered over each other to hold charge.

The type of capacitor that is of the most practical interest is the parallel plate capacitor

 Capacitors of various sizes, voltage, and capacitances....

Our Lab, we conducted an experiment by turning a book into a capacitor by using two sheets of aluminum foil separated by sheets of paper.

In this activity, first, we carefully cut two square pieces of aluminum foil and measured the area to be 0.0316 m^2 for each.  We then measured the thickness of a single page by averaging the measurement of the thickness of 280 pages. Dividing, a single sheet was approximately 6.357E-2 m.

We then connected a multimeter to the two sheets of foil using alligator clips. The positive end on one of the aluminum sheets and the negative end on the other. We measured the capacitance with the multimeter as the foils were separated by 1 sheet of paper.  Next, we repeated this process for 2, 10, and 15 sheets of paper and recorded the capacitance of each run.

Finally, we folded the aluminum sheets to half of the original surface area (0.0158 m^2) and measured the capacitance again for 1, 2, 10, and 15 sheets of papers.

 There are two sheets of aluminum foil of equal area inserted into the book with pages in between them. 

As we collect data for capacitance, we pressed down on the pages to minimize separation distance.  We need to minimize any air pockets to only account for the thickness of the paper sheets.  Any unwanted separation distance accounted for will cause greater inaccuracy.

Data collected per separation distance from trials

We took the data and plot the points using Excel to fit the equations. The blue curve represents the data taken from the original foil surface area and the orange curve represents to the halved of the original surface area.

Data as Capacitance vs. Separation Distance graph 

NEXT, WE BLEW UP A CAPACITOR!! WOOHOO~

Eye protection required!

After math debris poor little capacitor LOL

Next, we attempted circuitry using capacitors like we did using resistors.  We placed the capacitors in both series and in parallel then measured the voltage to determine a relationship between the configuration.

Capacitors in parallel (left) v.s. in series (Dez working in progress) (right)

Given the  two capacitors. The final capacitance we were able to observe that in parallel the capacitance of the capacitors was simply the sum of their respective capacitance.  On the other hand, when hooked up in series, the capacitance of the capacitors add up inversely:

Unlike resistors, the capacitors shows an exact opposite relationship as to resistors.In series 1/Ctot=1/C1+1/C2.  In parallel 1 Ctot=C1+C2.  

Look what Prof Mason brought out..... a bucket?  noooo, a capacitor!  This liquid capacitor is filled with PCBs a highly energy-concentrated but yet, TOXIC substance.

 DAAAAAANG!! LIKE A BOSS!!!

We ended class with a La Puente waste dump lesson:

Apparently they dumped 3.4 million gallons of PCBs in the 60s-80s at the BKK landfill.  RUN STEPHANIE RUNNN!!

Energy and Power in Circuits 4/16/2014

NO FIESTA TODAY???  AWWWWW~  After recovering from the feeling of disappointment by not having the highly anticipated fiesta, we started the class by going back to series-parallel circuits.

We were to hook up the battery & light bulb setup both in the series and parallel configuration.  We used the ammeter to find the current and voltage based on the different settings on this sophisticated tool.

We found some properties as follows as the fundamentals in circuit analysis:

In series, the voltage of the source is the sum of those in the resistors while the current stays constant.  In parallel, the voltage stays constant while the current is the sum.

Finally, the main attraction of the day was the introduction to resistors.  Prof Mason thoroughly explained how to interpret these cheap little bad boys.

Two different types of resistors with different cross-sectional area, the number of bands, and material (metal film v.s. carbon).
depending on

 Decoding the bands starting from the opposite side of tolerance band.

Real-life modeling of the diagrams

It is similar to an analogy to water running through pipes, when the resistors are in parallel, (the pipes doubles) more current can flow through and therefore, overall resistance goes down.  When the resistors are in series, the current has to pass through both so the overall resistance goes up (sum of the resistors).

Principles of resistivity 

Complex diagrams of resistors circuits

We were then given another circuit to practice and apply loop rules.  Based on Kirchhoff's laws, the voltage sum of every loop much be zero, we can then compute the three unknown currents.

Kirchhoff's Law of junction and sum of V =0

Elias computed using matrix??? maaan~ he OWNed those of us that used substitution!!!

Last but not least, we got hands on to build the circuit on a breadboard.  We needed to measure the currents and compare them to our values; however, we ran out of time.....

Current and Resistance 4/14/2014

We started with the electric potential fields analysis experiment.  In this lab, we took conductive paper that had a line and dot painted on it with metallic paint. A voltage supplier created electric potential difference between the line and dot via alligator clips. This voltage was measured as 15.02 V.  We then measured two points on the higher and lower voltage areas. The points measured on the higher voltage came out to be -0.62 V and the points on the lower voltage measured to be 1.37

We measure the electrical potential in various points in this in order to analyze a better understanding of the electrical potential difference and the relationship of the electrical field vs distance.

As the measuring distance increases, we plotted the measured values as follows:

Starting from the point, we measured the potential difference at 1 cm intervals going towards the line. We used excel to record the data and to create a  Potential vs Position graph as shown below.

The graph represents the the potential change with the distance from the power supply increasing. Looking at the data the positive charge goes from higher to lower potential.  Based on Eddie's epiphany, we conclude that the electrical potential goes up as the distance increases, therefore they have a direct proportional relationship.

THIS REMINDS US OF BURNT HOT DOGS!!

Equipotential 4/9/2014

Today we had our little fiesta... the question asks we to arrange two batteries and two light bulbs and make them 1) as bright as possible and 2) as dim as possible.  After the whole chaos of struggling to find the right setup, it turns out that the correct arrangement for brightest setup is to back to back the battery to double the voltage while keeping the light bulbs parallel.  As for dimmest setup, it is to keep the batteries parallel while  back to back the bulbs to double the resistance.

 Circuit with the series-batteries configuration (brighter = greater potential)

Circuit with the parallel-batteries configuration (dimmer = lasts longer)

After the fiesta, prof started the lab and used a much sophisticated immersion heater made out of resistive coils to heat a cup of water.  Similar to the beginning of the semester, we used a power meter to find power-supplied:

Experiment configuration hooked up to Logger Pro probe to plot data

By knowing the voltage and the mass of water, we first find the resistance of the boiling apparatus.  Given the mass of the water, the dimensions of the coil (cm long), and the applied voltage (4.5V), time (10 minutes) we can find the final temperature. Since our calculated resistance of the coil and the current flowing through  is different from other groups.  We then used then difference of resistivity different current to come up with an uncertainty for the current.  After determining the power, the energy put into the water, and the change in temperature with uncertainty, the actual change in temperature is as follows:

 (Click above images to see lab calculations on our whiteboards)

Next, we used the same process and changed the initial voltage from 4.5 volts to 9 volts. As calculated, it turns out that doubling the voltage did not double the change in temperature.  We then turned the spotlight to Eddie and put all the stress on him.  Eddie then finally says it would not have doubled because doubling the voltage also doubles the current, which increases the power by a factor of four.

Calculation of 4.5 V

Next, calculation of 9.0 V

Graph of the temperature change from logger pro. The blue data set was the 9.0 V experiment and the red data set was the initial 4.5 V experiment. According to logger pro, for the 4.5 V, T_initial was about 23°C and T_final at about 25°C for DeltaT of 2°C. The 9.0 V experiment initialed at 24.6°C and ended at 32.1°C for a DeltaT of 7.5°C.  it actually almost quadrupled. The reason for this can be shown mathematically.

When R remains the same, the new current is substituted into the power equation and the voltage increases 4x

Then we began lecture of an introduction of potential differences over a region.

Prof Mason demonstrates the perspective from a charge particle as it interacts with a positive potential (left) or a negative potential (right)

We wrapped up the day with a burnt hot dog party.  By putting a 110 volt (that is non lethal) through two different brand of hot dogs, we wanted to see other than the burnt stinky smell, if we were able to cook them with such electric potential.

 Ready to cook some dogs!!

LEDs instantly burned out due to massive overwhelming potential

EEEWWWWWWW~ STINKY DOGS SENSATION OF 1974!

We then stick little LED emitters into the hot dogs to see if they light up differently depending on the opening of their legs.  It turns out that the wider their legs are open, the brighter they glow before completely burning out.  This is due to the potential difference of power between the legs- greater difference = brighter.