Solderless Breadboards, Open-circuits and Short circuits Lab

Purpose and class objective: 

We examine the resistance using a digital multimeter when connecting to different holes in our breadboard. The multimeter serves to read the resistance from which we will see whether connecting different nodes in the same row or in different rows will acquire a difference of resistance in ohms. We will also do in class practice using the idea that summation of power equals to zero or in other words the conservation of energy law. We will also practice the idea of P=IV, I=V/R, and graphical representation of current, energy, voltage, and power using calculus. 

Reviewing Circuits:

We reviewed the idea that electric current is the change of charge divided the change in time in which it is measure in Amperes. We can also manipulate the equation to calculate the charge between some time by integrating the current with respect to time. Furthermore, we reviewed graphical representation of direct current for which is constant and alternating current for which it  varies sinusoidally with time. With this in mind we can also acquire a mathematical equation for voltage where v = dw/dq where dw is the change represents the energy and dq the charge in coulombs. In the end, we can find Power where P= IV = dq/dt*dw/dq = dw/dt. Finally, we covered the idea of dependent and independent sources. 

Lab Procedures taken:

1. Our first step is to connect leads of the DMM using jumper cables to two hole that are in the same row on the breadboard as seen in Figure 1. The result shows 21 ohms. However, it seems to be inconsistent as it increases and decreases suddenly. Yet, we acquire a reasonable resistance measurements of 21 ohms. From this we can conclude that step 1 is a closed circuit since there is still a flow of current based on the idea that I = V/R 

Figure 1. Using a digital multimeter (DMM), there is a low resistance when the two leads of the DMM are connected on the same row. This is step 1 of the lab procedures. 

2. The second step is to connect the leads on the same row of the breadboard but on opposites sides of the central channel as seen in Figure 2. From this procedure, we acquire an infinite resistance which shows that there is no current flow since I = V/Inf = 0. Therefore, we can conclude that step 2 of the lab is an open circuit. 

Figure 2. The second step of the lab shows that the DMM reads an infinite resistance when connected on the same row on opposite sides.

3. The third step shows gave us an infinite resistance as shown in Figure 3. However, in this case, the connectivity was no in the same row but in different rows. As a result, we concluded that step 3 of our lab is a open circuit since there is no current flow when the resistance goes to infinity. We can see that there is no current flow since they do not lie on the same row. 

Figure 3. The third step of the lab shows the same infinite resistance as step 2 but when connected between two holes not in the same row.

4. Step 4 of the lab uses the same step as in step 3 where the DMM is connected on different rows. However, we added a jumper cable between the nodes as seen in Figure 4. We measure a resistance of 3.9 ohms which is very low than from step 1 result of 21 ohms. Since there is a low resistance, then, there is current flow. This means that step 4 is a closed circuit.

Figure 4. A low resistance of 3.9 ohms was measured from step 4 which shows that it is considered a closed circuit. 

In class Practice Procedures:

The circuit as seen in Figure 5 shows a variety of voltages and current flow measurements. The objective is to find the unknown voltage. We can see that we are given an ideal voltage source where the power absorbed by the voltage source is -150 watts. According to the law of conservation of energy, we add all the power where P = IV and equal it to zero. By using algebra, we can find for the unknown voltage for which we found it to be 20 volts.  

Figure 5. In class practice with lab partners on dealing with a circuit of different voltages and currents. 

Summary: 

We covered the idea that a short circuit involves the resistance approaching 0 and an open circuit involves a resistance approaching infinity. Yet, a short circuit can still show a current and can be anything while the current an open circuit is 0 since I = V/R. Furthermore, we can point out that current flowing from a lower potential to a higher potential is V = -iR and current flowing from a higher potential to a lower potential is V=iR.