Mr. Rogers' AP Physics C: E&M (with IB Physics) Objectives Syllabus 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter IB Objectives 3rd Q objectives small investigations IB internal assessment write up specs IB rubrics
Physics Investigations

Physics E&M  Investigations

Presentation of the AP Physics content for E&M will be finished some time in Dec. Starting in January a substantial amount of class time will be devoted to performing hands-on physics experiments in order to answer the essential question shown below:

 Essential Question: Do the mathematical models and principles of physics actually work?

Relavance: Therory needs to be confirmed by experiments.

The investigations selected below are intended to help meet the IB internal assessment standards

 Investigation 1:  Investigation of shielding IB Standard: Rubrics Purpose / Research Question :  Can shielding prevent unwanted electric fields from producing noise signals in wires? Instructions: Wrap about 3 feet of unshielded single conductor wire into a coil about 10 inches in diameter. connect the two ends to an oscilloscope and place the coil atop a similar sized coil of an extension cord plugged into the wall. Observe the noise signal picked up by the single conductor wire. Wrap an aluminum foil shield around the single conductor wire and connect one end of it to the oscilloscope's ground. Again observe the noise signal. Equipment: oscilloscope, 3 ft of unshielded wire, extension cord Data, Calculations: Record your observations. Questions, Conclusions: What does Gauss's Law indicate about the e-field inside a charged conductive surface in electrostatic equilibrium? How does the above situation relate to the conditions of the experiment? What is different? Safety: Deliverables (formative / summative assessment): An Excel spread sheet with

 Investigation 2:  Investigation of a light bulb's resistance IB Standard: Rubrics . Purpose / Research Question:  Determine if a a light bulb follow Ohm's Law. Instructions: For a device following Ohm's Law, a plot of current vs. voltage drop across the device will be linear with a slope = 1 / R. Regression analysis can give us a curve of best fit for the data along with an indicator of the fit's quality (R-square). Residuals analysis can indicate whether a linear fit is or is not appropriate. If it is not then the device being tested does not follow Ohm's law. (Note: if you have not taken AP Statistics Mr. Rogers will assist you with making the statistical analysis.) Connect a variable DC power supply ammeter and voltmeter to a low voltage light bulb. Remember, the light bulb, power supply, and ammeter will be in series. The voltmeter will be connected in parallel with the light bulb. Note the power supply should be turned off and adjusted to its lowest voltage setting. Turn the power supply on and slowly adjust the voltage upward while collecting current vs. voltage data points. Stop when the light bulb is at its rated voltage and is glowing brightly. Plot a current vs. voltage drop curve for the device and perform regression analysis as well as residuals analysis. Repeat the process for a commercial resistor. . . Equipment: 12 volt light bulb, a resistor designed for high power, variable DC power supply, ammeter, multimeter (voltmeter), wires Data, Calculations: See deliverables. Questions, Conclusions: Does a light bulb follow Ohm's law? Safety: Shorting out the power supply can damage the unit and burn up wires. Remember, an ideal ammeter has a resistance = 0. If you connect it across the power supply without placing the light bulb or resistor in the circuit, the power supply will be shorted out. Putting excessive current through the resistor will overheat it and create a burn hazard. Note: To prevent overheating of the elements in your circuit, turn the power switch off and adjust  the voltage knob on the variable power supply to its lowest setting before connecting wires. When ready to start the experiment, turn the power switch on and adjust the voltage up slowly while monitoring the temperature of the circuit. Equipment Limitations: Subjecting the light bulb to more than its rated voltage will burn it out. Remember, a light bulb glows because it reaches very high temperatures. If the bulb glows brightly and is then turned off it will take some time for it to return to its original temperature. This could affect your results. Note: TURN THE MULTIMETER OFF WHEN FINISHED! It is battery operated. Deliverables (formative / summative assessment): For both the light bulb and resistor: an Excel spread sheet with a scatter graph of current vs voltage with a linear trend line of best fit showing the equation and R-squared values along with a residual plot of the data indicating whether or not the line of best fit is appropriate or not.

 Investigation 3:  Analysis of circuits with resistors in parallel and series IB Standard: Rubrics Purpose / Research Question:  Do the equations for calculating total resistance actually work? Instructions: Determine if the equations for calculating the total resistance of series an parallel circuits actually work. Configure 3 resistors in series and measure the total resistance of the circuit. Configure 3 resistors in parallel and measure the total resistance of the circuit. Configure two different  combination parallel and series circuit with a minimum of 5 resistors in each circuit. Measure the total resistance of the circuit. Be sure to record a drawing of each circuit. Note: use the color code to select resistors, keeping in mind that you will not be able to measure total resistance if the resistance is too high or too low. However, measure the resistance of each with the multimeter and use this number in your calculations. Note: TURN THE MULTIMETER OFF WHEN FINISHED! It's battery operated. Equipment: multimeter, various resistors, solderless breadboard Data, Calculations: Calculate a total resistance for each circuit configuration and a % difference from the measured value Questions, Conclusions: Why is it better to use the measured values for each resistor when calculating the total resistance rather than using the official manufacture's values? Why would we use the term "% differences" rather than "% error" ? What assumptions are implicit in the models you used to calculate the total resistance? What additional experimental errors did you introduce when using the multimeter? Safety: The wires on resistors as well as the multimeter probes can inflict puncture wound. Deliverables (formative / summative assessment): A Word document with a sketch of the circuits, a data section and a conclusion.

 Investigation 4:  Investigation of Kirchoff's Law IB Standard: Rubrics Purpose / Research Question:  Do the voltage differences around a closed loop in a circuit actually add up to zero? Instructions: Create a circuit with 2 loops in it and at least 3 resistors. Measure the voltage differences around all 3 loops. Equipment: multimeter, various resistors, solderless breadboard, power supply Data, Calculations: Sum of voltage differences  around the loops Questions, Conclusions: Answer the research question using the data from the 3 loops. Safety: Be sure the power supply is set to the lowest practical DC voltage. Starting at around 30 volts, a current can be harmful to humans. Hazards can include burns and in the worst case (usually with AC power) can disrupt the electrical activity of the heart leading to unconsciousness and possibly death. Make all connections with the power turned off. Do not touch bare wires or terminals after the power is on. Carefully check your circuit for shorts before turning power on. Shorting out the power supply will at best blow its fuses. in the worst case it will cause a fire. Deliverables (formative / summative assessment): A Word document with the data calculations, and a sketch of the circuit.

 Investigation 5: Measurement of the Speed of Sound IB Standard: Rubrics. Solve problems involving the fundamental and higher harmonic modes. Purpose / Research Question: Measure the speed of sound in aluminum using wave equations Instructions:Create a pure sine wave by making an aluminum rod resonate. Measure its frequency using both a frequency and time plot.. Equipment: Aluminum rod, meter stick, resin, Android Phones Data, Calculations: frequency from the time plot. Speed of sound in aluminum from 1st harmonic anaylysis.. Questions, Conclusions: Does the measured speed of sound match with accepted values? How long would it take sound to travel from one end of the rod to the other How feasible would it be to measure this time in some other manner? If you input a sound at one end of an aluminum rod, would the sound have the same frequency when heard at the other end? Would it have the same wavelength? Safety: The sound is very loud and should be experienced for only short durations. Deliverables (formative / summative assessment): calculations as described above.

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