The Voltage Divider Key to Big Ideas Practical
The Voltage Divider Key to Big Ideas • Practical Implementation of Circuits • Theory-Simulation-Experiment (Compare & Contrast) • Direct Uses (Finding ZIN or ZOUT, Voltage Standard, Model for Filters and Other Types of Circuits …) • Fundamentals (Ohm’s Law, Linear Systems …)
The Voltage Divider Note that there are several points in this video where you are encouraged to pause and think about a question. To do this you will have to press Pause (lower left on You. Tube window) and then Play when you are ready to proceed. You will be reminded of this with the following symbol: 02 October 2020
The Voltage Divider Before Addressing the Voltage Divider, Recall Ohm’s Law • From Wikipedia • Plot Current I vs Voltage V • Slope is Outcomes Large Resistor: Small Current Small Resistor: Large Current (Same Voltage) 02 October 2020
The Voltage Divider 02 October 2020
The Voltage Divider 02 October 2020
The Voltage Divider • Where Does the Formula Come From? 02 October 2020
The Voltage Divider • Where Does the Formula Come From? 02 October 2020
The Voltage Divider • Can the Formula Be Used in Other Ways? Knowns Unknowns Vin, R 1, R 2 Vout If we can measure any three, we can determine the 4 th 02 October 2020
The Voltage Divider • Can the Formula Be Used in Other Ways? Knowns Unknowns Vin, R 1, R 2 Vout R 1, R 2, Vout Vin, R 2, Vout R 1 Vin, R 1, Vout R 2 What happens if we have 2 unknowns or even more? What experiment can we do to figure out all four parameters? Are there other reasons to make more than one set of measurements? 02 October 2020
The Voltage Divider • Finding Unknown Resistor Does this answer make sense? Battery as Source: • Unknowns are Vin and R 1 (Vbat varies with time so not known exactly) • Measure Vout with no R 2 connected (open circuit load) • Vin = Vbat = Vout (open circuit) • Connect R 2 with value similar to guess for R 1 • Determine R 1 from Voltage Divider Equation 02 October 2020
The Voltage Divider • Finding Unknown Resistor Does this answer make sense? Battery as Source: • Unknowns are R 2 and Vbat • Use R 1 with a value similar to your guess for R 2 • Measure Vout with no R 2 connected (open circuit load). • Connect unknown resistor R 2 • Use Voltage Divider formula to find R 2 02 October 2020
The Voltage Divider • Can find Input Impedance for Most Black Boxes Using this Method • Also Useful for Resistive Sensors 02 October 2020
The Voltage Divider Example of Resistive Sensors • Photocell (LDR) – Resistance changes with light level • Strain Gauge – Resistance changes slightly when stretched or compressed • Force Sensor (FSR) – Resistance changes with pressure DIY Strain Gauge 02 October 2020
The Voltage Divider R 2 is Resistive Sensor 02 October 2020
The Voltage Divider To Be Continued … 02 October 2020
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