02/25 - Lab 2: Resistors and Ohm's Law and Lab 3: Dependent Sources and MOSFETs

Lab 2 - Resistors and Ohm's Law: Voltage-Current Characteristics

In this lab, we explored the nature of resistors and how they affect voltage and current. We connected a resistor in series with the power supply with a multimeter in parallel to read the voltage drop across the resistor.

Equation: y = 9.216x -0.0217, R^2 = 1

The data shows that voltage and amperage share a linear relationship in a circuit containing only a resistor. This result is expected due to the equation for voltage V = IR.

Lab 3 - Dependent Sources and MOSFETs

In this lab, we explored the topic of dependent sources by examining how voltage and current behave with a MOSFET added to the circuit from the previous lab

MOSFETs are voltage-dependent current sources, which means they control the current in a circuit based on the voltage entering the gate G. Similar to a diode, MOSFETs have a threshold voltage that must be met in order to pass current through. According to the data collected, the gate of the MOSFET "cracks open" at 1V, and from 2V up to 2.5V the gate really opens up, allowing a flood of current though. From 2.5 V to ~4.5 V, the current plateaus at ~48 mA. Above ~4.5V, the MOSFET severs the circuit. The slope of the line obtained through this period is 68.5, which represents the gate g of the MOSFET. Thus, g = 68.5 A/V. 

In Class Examples

1) Given an incandescent light bulb rated at 75 watts and 120 volts, find the “hot” resistance and “cold” resistance of the light bulb. The filament is made of tungsten (52 × 10-8 Ωm)

2) Determine the number of branches, loops and nodes in the circuit shown below. Check Fundamental Network Thm.

3) Find I and Vab in the circuit for all four cases of polarity in the voltage supplies.