Resistors and Ohms Law, Dependent Sources and MOSFETs

Resistors and Ohms Law – Voltage-Current Characteristics

In this lab, we wired a simple circuit containing a voltage source and a 100 Ω resistor to examine the relationship between voltage and current. We used WaveForms and Analog Discovery interface to simulate a DC voltage and measured the corresponding current with a digital multimeter (DMM).

Before wiring the circuit, we used the DMM to measure the actual resistance of the 100 Ω resistor. We got a 97.9 Ω reading on the DMM.

We then wired the circuit according to the diagram and took several readings for current as we increased the voltage from 0 V to 2 V in increments of 0.2 V.

Using this data, we created a graph of current vs. voltage. We noticed that the relationship between current and voltage was linear. We fit a linear trendline and obtained the equation for the line. The slope of the line is y=0.1084x. The slope, 0.1084 represents the resistance of the 100 Ω resistor. However, since the current was measured in mA, the resistance is given in MΩ. Therefore, the experimental resistance for the 100 Ω resistor was 0.1084 MΩ or 108.4 Ω. The R^2 value is 1 so the data points fit right on the trendline.

When we compare the calculated values from the graph to the original measured value, we notice that there is a difference of about 10 Ω. This may be due to the resistance in the circuit wires since we initially measured the resistance of the 100 Ω resistor directly, without using any wires in addition to the DMM ones.

Solderless Breadbords, Open-circuits and Short-circuits

In this lab we analyze open and short circuits on a breadboard. We connect wires to the breadboard in various configurations and use a digital multimeter (DMM) to measure the resistance in each configuration. Using this information we determine whether we have an open circuit or a short circuit.

First, we connected the two wires in the same row. The DMM read 0.5 Ω,

Next we set the wires on the same row but on opposite sides of the central channel. The DMM reading was 2.21 MΩ.

Next, we set the wires on the same side of the central channel, but not on the same row or column. The reading on the DMM was 1.80 MΩ.

Finally, we connected two green wires on opposite sides of the central channel, but not on the same row. We used a third yellow wire whose ends were connected to the same row of each individual green wire. The reading on the DMM was 0.6 Ω.

After analyzing the data, we noticed that the first and last wiring configurations had very low resistances and the second and third wiring configurations had very high resistances. The low resistance configurations approached zero resistance while the high ones approached infinity. This suggests that the first and last configurations were closed circuits and the second and third configurations were open circuits.

This tells us valuable information about how the breadboard works:

• The two sections separated by the central channel are independent from one another.
• Anything plugged in to the same row on the same side of the central channel are connected together.
• A row on one side of the central channel can be connected to any row on the other central channel by connecting a wire that goes from one side to the other.