Equipment List:
    hand-held DMM
    HP-DMM
    DC power supply
    Resistor and light bulb circuit board
    Assorted red and black bananas and alligator clips

WARNING: THROUGHOUT THIS LAB, YOU SHOULD NEVER DIRECTLY MEASURE THE RESISTANCE OF A RESISTOR WHEN THERE IS A CURRENT ALREADY THROUGH IT FROM A POWER SUPPLY. DOING SO MAY DAMAGE A METER. FOR THE SAFEST APPROACH, ONLY MEASURE  RESISTANCE  DIRECTLY USING AN OHMMETER WHEN THE RESISTOR IS REMOVED FROM A CIRCUIT.

Goal and Procedure:
1. Determine the resistance of the "power resistor" found on the circuit board provided by calculating a slope from measured data and relating the slope to the resistor's value:  Construct the circuit shown in the diagram below or in your lab's lecture. First construct the circuit, then connect your two meters. Use the HP-DMM as the ammeter and the hand-held DMM as the voltmeter. Prepare your lab book so that you can record your data and draw your graph at the same time, point by point.
Your graph should be a full page graph.

Take your data by starting at a low voltage value (e.g. less than five volts) and record the voltage across the resistor and the current through the resistor. Increasing the voltage each time, repeat your measurements four more times for a total of five different pairs of voltage and current readings. Each successive data point will represent an increase in voltage and current readings. Plot the voltage on the horizontal and the current on the vertical axis; this graph is called a "characteristic curve" of the resistor.

Draw an "eyeballed" straight line using your ruler that best represents the line formed by the data points.

Graphing tips:
Don't use the origin as a data point. Don't connect one point to the next point, draw one straight line. Don't "force" the line to intersect as many points as possible; the best fit line may not intersect any data points.

Use the data points to determine the line, and you use the line, not the data points, to determine the slope. For the slope, choose two points on your drawn line (not data points!) that span a large part of your graph, ideally outside all your data points.

Calculate the resistor's value by applying Ohms' law and understanding how the slope of the graph is related to the resistance. Compare your value to a direct measurement from the HP-DMM

2. Now incorporate the light bulb "in series" with the power resistor. Change the voltmeter leads to read the voltage across the light bulb. DO NOT EXCEED SIX VOLTS ACROSS THE LIGHT BULB OR THE BULB WILL BURN OUT! Take twenty data points varying the voltage on the power supply so that the voltage across the bulb goes from  less than a volt to almost six volts. Graph the data on the computers.  Calculate the resistance of the bulb at a small current and then at a relatively large current. Is it correct to use the tangent line to the curve to determine the resistance of the bulb? Think about it because the answer is NO (then how do you determine the resistance of the bulb from the graph?). For curve fitting on the graph, you might try a "power" fit.

More: In the previous lab, you measured your skin resistance between two points. Knowing that value, use Ohm's law to calculate the current through you if nine volts were applied across the same two points.