Lab & Pre-lab #5: Voltage

More documents

Recommendations

Info

Fundamentals of Circuits III: Voltage & Ohm’s Law v 0.1Question 3.5 Based on your graph, what can you say about the value of R for a resistor–is itconstant or does it change as the current through the resistor changes? Explain.Question 3.6 From the slope of your graph, what is the experimentally determined value of theresistance of your resistor in ohms? How does this agree with the value written on the resistor?(Remember that your resistance has a tolerance coded on it.)Note: Not all circuit elements obey Ohm’s law. The definition for resistance is still thesame as the relation you obtained, but the resistance changes as the current changes. Circuitelements that follow Ohm’s law–like resistors–are said to be ohmic, circuit elements that do notare called non-ohmic.In the last activity you explored the relationship between the potential difference across aresistor and the current through the resistor. It is a proportional relationship. In the followingextension you will explore the relationship between current and potential difference for a lightbulb instead of a resistor.Extension 3-2: Relationship between Current and Potential Differencefor a Light BulbStep 1: Connect a light bulb in the place of the resistor, as shown in the circuit in Fig. 10.CP2DC Power Supply+−+ −+−VP1Figure 10: Circuit with a variable power supply to explore the quantitative relationship betweenthe current and potential difference for a light bulb.Prediction 3.4 What do you predict will happen to the brightness of the bulb as you turnthe dial on the power supply and increase the voltage from zero? Explain.Prediction 3.5 What do you predict for the mathematical relationship between the voltageacross the bulb and the current through the bulb?PHYS-204:Physics II Laboratory 15
Fundamentals of Circuits III: Voltage & Ohm’s Law v 0.1Step 2: Prepare to graph current vs. time with current probe 1 and voltage vs. time withvoltage probe 2. (Adjust the horizontal axis on the top graph back to time, and adjustthe horizontal scale to give a range from 0 to 30 seconds).Step 3: Begin graphing with the power supply set to zero voltage, and graph current andvoltage as you turn the dial and increase the voltage slowly to about 3 volts.Warning: Do not exceed 3 volts, since this may burn out the bulb! Also,return the voltage of the power supply to zero as soon as you are done withyour measurements.Question E3.1 What happened to the brightness of the bulb as the power supply voltagewas increased? How did this compare with your prediction?Question E3.2 How is the brightness of the bulb related to the potential difference acrossthe bulb? To the current through the bulb?Step 4: You can again display a graph of potential difference vs. current by changing thevariable on the horizontal axis on the bottom graph to current as before.Voltage 1(V)Current 2 (A)Current 2 (A)Time (s)Question E3.3 Compare your graph of voltage vs. current for the bulb to that for theresistor in the previous activity. In what ways are they similar, and in what ways are theydifferent?Step 5: Use the fit routine in the software to determine if the relationship between voltageand current for a light bulb is a proportional one.Step 6: Sketch the graphs, or print and affix them over the axes.PHYS-204:Physics II Laboratory 16
Page 1 and 2: Name:Lab Partners:Date:Pre-LAB 5 As
Page 3 and 4: Fundamentals of Circuits III: Volta
Page 15: Fundamentals of Circuits III: Volta

Lab & Pre-lab #5: Voltage

Create successful ePaper yourself

Delete template?

Save as template?