Sunday, February 5, 2017

Week 4 Blog

   Week 4
1. Ic vs Vbe table and graph
Table and graph expressing the quick amplification of the current done by a transistor once VBE approaches .7 V. 

2. (Table and graph) Create the graph for IC (y axis) versus VCE (x axis). Vary VCE from 0 V to 5 V. Do this measurement for 3 different VBE values: 0V, 0.7V, and 0.8V.

This graph and table shows the relationship between the collector-emitter voltage and the collector current. This plot shows that once the collector current reaches a certain value, the collector-emitter voltage increases. We think the reason VBE=.7 V is so much lower than VBE=.8 V is because the current is so low that the transistor is operating in the cut-off region, no amplification happens in this region.

3. (Table) Apply the following bias voltages and fill out the table. How is IC and IB related? Does your data support your theory?
This table shows the relationship between the collector current and the base current. Due to one of our group members having already taken EGR 298, it isn't so much of a theory as it is an educated answer, but this shows that a small base current can be amplified to be a much greater collector current without having to change the voltage being applied to the collector at all. The factor to which the base current is amplified is called the gain, and is represented as greek letter capital beta. The equation that shows this relationship is typically Ic = β*Ib.

4. (Table) Explain photocell outputs with different light settings. Create a table for the light conditions and photocell resistance.

Phone Flashlight
265 ohm
Completely Covered (No Light)
11.5 kohm
Regular (No cover or added light just the lights from the ceiling)
2.48 kohm
Table showing the relationship between light levels and resistance in a photocell

5. (Table) Apply voltage (0 to 5 V with 1 V steps) to DC motor directly and measure the current using the DMM.

0 V
0 mA
1 V
28.5 mA
2 V
35.7 mA
3 V
42.1 mA
4 V
48.6 mA
5 V
52.5 mA
Table showing the measured values of current and voltage in a DC motor

6. Apply 2 V to the DC motor and measure the current. Repeat this by increasing the load on the DC motor. Slightly pinching the shaft would do the trick.

~~When we set up the 2V to the DC motor no pressure on it gave a current reading of 35.6 mA, lightly pinching the shaft gave 62.8 mA, applying a more pressure gave 81.9 mA, and finally pinching it with more pressure than previously gave a current reading of 97.5 mA which was enough pressure to cause the DC motor to stop.

No Pressure
35.6 mA
Light Pressure
62.8 mA
Heavy Pressure
81.9 mA
Motor Stop
97.5 mA
Table showing how the DC motor actively resists outside forces. The more pressure applied the more current that was measured.

7. (Video) Create the circuit below (same circuit from week 1). Explain the operation in detail.

Video explaining what is happening in and around the transistor in the Rube Goldberg circuit

8. Explain R4’s role by changing its value to a smaller and bigger resistors and observing the voltage and the current at the collector of the transistor. 

~~R4's role, which is also the 47 ohm resistor, is used to not let excessive current damage the transistor. Because of Ohms's law when the resistor is less the current value is bigger, and when the resistance is increased the current value is less. Which is what happened in our experiment. When we used a lessor valued resistor the current increased relevant to the 47 ohm resistor, and when we used a resistor that was greater then 47 ohm's the current value was less compared to the 47 ohm resistor.

9. (Video) Create your own Rube Goldberg setup.

A video demonstration showing the potential of the Rube Goldberg circuit


  1. You first graph has a fitted curve line that represents a exponential function, which is a bit deceiving being that after a certain voltage, the curve begins to level out with a derivative approaching 0. I'd suggest that if you include the fitted curve, it follows your measured values more. More measurements may be needed between 0.5 and 1 V.

    1. Thank you Nicholas, I believe you are right. Obviously, the current will not continue to climb to infinity because this is just simply impossible. Unfortunately by the time I saw this comment, there wasn't any time to get more values.

  2. at the time of my commenting the your blog is still unfinished. Just a bit of text added to explain graphs and tables and you're good. Your question number 8 was different then my groups. We found that our collector current change very little when we change our R4's value.

    1. Hmmm, that surely is interesting Dru. Mary was the person in our group who set this circuit up so she would definitely be more knowledgeable than I, but it seems to me that adding/removing a resistor would definitely affect the current, otherwise why include it in the circuit?

    2. For 8 I didn't mean for it to sound like it was a huge difference. I just meant that there was enough difference between the resistors to note a change.

    3. It always tricky trying to figure out what the correct values are. Could you recommend some tips that would help us obtain better results for Week 5 blog?

  3. Nice work on the graphs, I like the line of best fit in problem 1. Though I must say I think your Rube Goldberg machine still needs a bit of work.

    1. We were taking a simple approach with it at first. We needed to fulfill the requirements for the lab. This lab was very tricky for us, so we were crunched for time. Even while using the open lab hours. The Rube Goldberg does not need to be a master piece for another 10 weeks! We have some time to make some improvements.