[Thur Feb 2] Voltage, Resistor, Current, Power

Today we continued learning about circuits. We introduced Ohm's Law and the relationship between voltage, current, resistor and power (V= RI, P=VI). We also learned voltage can be added together, such as when we connect batteries in a series. I learned most of them in physics but I practiced some of the knowledge into applications today. For example, I learned that the alternating current (AC) is influenced by alternating voltage, which is between 167V and -167V in the US, and I interpret it as if it were direct current, it would have been 110V, which is the voltage electric appliances use here.

Then we started to build circuits. I had built circuits before in physics, but not on a breadboard. It is too hard to describe, so I found a picture:

http://www.szeblog.cn/user2/14598/63771.html

I used ammeter and voltmeter and connected the circuit directly. I thought it was way easier that way because I can see clearly what is going on. However, I didn't deal with connecting to the ground before, and I wonder whether that comes in the circuits that I built before. Anyway, the tools that we built today looked a lot more sophisticated than mine before. And I found the concept of different voltage at different rows and lines hard to get used to. 

As shown above, there are five antennae on the power source and we first connected four of them to 12V, -12V and 0V (later it proved that we only needed to connect three). Then we plugged the power source in and connect one end of the probes (ground) to 0V on the board. After that, we connect a wire to the probe and use the other end of the wire to test different spots on the circuits. It didn't show the correct measurement for a long time and Oscar helped us to debug. We first realized that we were using 1X instead of 10X, so we switched that; then we checked that our yellow probe was not working, so we changed a new probe. Then we realized that we didn't have to connect one of the antenna of the power source so we got rid of that. Then Oscar disconnect two antennae from the power source for the reason that I didn't figure out and it worked. Our final circuit looks like this:

And the whole setup looks like this with the oscilloscope:

Later we talked about voltage divider: how resistors share voltage when they are in series and parallel with each other. In series, they act at one big resistor with the ohms of several resistors added together. In parallel, they act as a resistor with (R1 * R2)/(R1+R2) ohms. I learned this before and have dealt with more complicated circuits, but only on paper. My partner and I tried to do series and the results from the oscilloscope do agree with the rule that we learned. We ran out of time to do resistors in parallel, but here are the circuit diagrams for resistors in series and in parallel:

In general, today's paperwork was easy for me. But applying these paper work to a circuit board was new and challenging to me.