Mr. Rogers' AP Physics C: E&M (with IB Physics) Objectives |
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Syllabus | 1st Quarter | 2nd Quarter | 3rd Quarter | 4th Quarter | IB Objectives |
C. Electric circuits ..................................................................20%
1. Current, resistance, power
2. Steady-state direct current circuits with batteries and resistors only
3.Capacitors in circuits
a. Steady state
b. Transients in RC circuits *
Ohm's Law (Chap. 27 Serway)
Voltage, Current, Resistance
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Voltage, Current and Power in Houses
Homefun: Questions (page 790-791) 2-9, 17, 18, 20; Prob. (page 790-791)3, 15, 21, 25, 43, 53 Relevance: Houses are all wired with parallel circuits. All of the devices inside a house can be modeled as resistors. Summative Assessment: Test on objectives 1-13 |
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Formal Physics Investigation |
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Title | Does a light bulb follow Ohm's Law? |
Purpose | Determine if a a light bulb follow Ohm's Law. |
Models | Ohm's Law. |
Overview | 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.)
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Safety Issues | 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. |
Resources/Materials: | 12 volt light bulb, a resistor designed for high power, variable DC power supply, ammeter, multimeter (voltmeter), wires |
A. Electrostatics .....................................................................30%
1. Charge, field, and potential
2. Coulomb's law and field and potential of point charges
3. Fields and potentials of other charge distributionsa. Planar
b. Spherical symmetry *
c. Cylindrical symmetry *4. Gauss's law *
Electric Potential (Chap. 25 Serway)
Essential Question: Could you draw free electrical power out of the air using an antennae? |
State whether electric potential is a vector or scalar and give its units.
Explain the difference between negative and positive work. Positive work increases kinetic energy. Negative work decreases kinetic energy.
Write the generic electric potential difference equation.
- ∫ b ΔV
= E • ds a
By convention, positive charges move from high to low voltage. Since ΔV = (Vlow - Vhigh), ΔV will be a negative number when the positive charge is gaining kinetic energy. The right hand side of the equation calculates the work done and positive work indicates an increase in kinetic energy. The negative sign on the right side is needed so that a negative ΔV yields an increase in kinetic energy.
ΔV
= E • x Homefun (formative summative assessment): p.714-716 1, 3 13
Essential Question: How is the E-field around a point charge similar to the gravity field around a planet? |
- ∫
r (Vr - 0)
=
(kQ / r2 ) • dr
∞
Calculate the electric potential from more than one point charges. (Note: voltages are not vectors. the positive and negative sign on them does not have anything to do with spatial direction. Positive charges generate positive voltages, negative charges negative voltages.)
Relate the electric field to electric potential mathematically and conceptually. Be sure to add the minus sign. Remembering this fact can sometimes make a difference.
E = - dV / ds
Electric field lines are always perpendicular to equipotential surfaces or lines
Why?
dV = - E ∙ ds
This is a dot product, so for E ≠ 0, dV can only be zero if E is perpendicular to ds. Therefore, if ds is the displacement along an equipotential surface, E must be perpendicular to it because dV = 0 along an equipotential surface.
Homefun (formative summative assessment): p.731: 1, 3, 11,12, 33
Homefun (formative summative assessment): page 717-738; 27, 32, 43
Electric Potential Fun with Fuzzy and Non-fuzzy Spheres and Cylinders
(Fuzzy stuff dejavu, yippy!)
Essential Question: Why can a bird land on a high voltage wire and not be electrocuted ? |
ring v = kQ / ( x2 + a2 )0.5
disc v = 2πkσ [ ( x2 + R2 )0.5 - x ]
Be aware that current, if there is any, will always flow in the direction of the E-field or from high voltage to low voltage.. For E = 0, The voltage could be anything as long as it is constant.
Derive an expression for the electric potential inside and outside various types of spheres with radius = R.
outside: v = kQ / r
inside: Note: the voltage does not equal zero at the center of the sphere for any of the cases shown below.
charged solid conductive sphere : E=0, therefore electric potential is constant throughout sphere, v = kQ/R
charged hollow conductive sphere: E=0, thereforeelectric potential is constant throughout sphere, v = kQ/R
uniformly charged nonconductive ("fuzzy") sphere: here there is an E-field inside the sphere because the charges cannot move around. v = [ ( kQ ) / ( 2R ) ] ( 3 - r2 / R2 )
Calculate the charge distribution when a charged conductive sphere is connected to an uncharged one. Note: the charge stops flowing when the the voltage is the same on both spheres.
Homefun (formative summative assessment): page 717-738; 55, 57
Summative Assessment: Test on objectives 1-16
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Title | Analysis of Circuits with Resistors in Parallel and Series |
Overview |
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. |
Data, Calculations | Calculate a total resistance for each circuit configuration and a % difference from the measured value |
Questions, Conclusions |
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Resources/Materials: | multimeter, various resistors, solderless breadboard |
C. Electric circuits (continued)..................................................................20%
1. Current, resistance, power
2. Steady-state direct current circuits with batteries and resistors only
3.Capacitors in circuitsa. Steady state
b. Transients in RC circuits *
DC Resistance Circuits (Chap. 28 Serway)
Essential Question: How do various common circuit components compare to mechanical components? |
Homefun (formative summative assessment): 8 (will be formally graded), 9, 15, 21, 23, 31, 33, 55 p. 800-805
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Title | Investigation of Kirchoff's law |
Purpose | Determine if the sum of the voltage drops around a closed loop = zero |
Overview |
Set up a circuit with a power supply and 3 loops in it, one big
overall loop and 2 small ones (similar to a "B"). Place a known
resistor in each segment of each loop. Measure the voltage drops
around each segment for each loop to see if the voltage drops do
indeed add up to zero. Be careful not to short out the power supply. |
Data, Calculations | Collect the information for all 3 loops. |
Questions, Conclusions |
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Resources/Materials: | multimeter, various resistors, solderless breadboard, variable power supply |
D. Magnetostatics.................................................................20%
1. Forces on moving charges in magnetic fields
2. ForcesD. Magnetostatics.................................................................20%
1. Forces on moving charges in magnetic fields
2. Forces on current-carrying wires in magnetic fields
3. Fields of long current-carrying wires
4. Biot-Savart and Ampere's law *
Essential Question: Is the North Pole the North Pole? |
How Can We Describe a Magnetic Field?
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How to Design an Electric Motor/Generator
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How to Design a Mass Spectrometer Mass spectrometers are considered one of the most sensitive and accurate ways to identify unknown substances or to measure very tiny amounts of a known substance, such as in air pollution monitoring.
Homefun (formative summative assessment): 5, 6, 13, 15, page 856 |
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Title | Investigation of a simple DC Electric Motor |
Purpose | Determine how to fabricate the coil on a simple DC electric motor so that it rotates when supplied with a voltage source. |
Overview |
Wind the enamel coated copper wire around the mandrel to make a
coil as shown in the handout provided. This coil will be placed
in the holder provided and become the rotor for a simple
electric motor. Correctly scrape off the enamel coating on the coils electrical contact points. Remember, for a DC motor to work, Either the current must be reversed every half turn or the current must be turned on for only half a turn. Otherwise the torque will flip-flop and prevent the motor from rotating. The simple motor will turn the current on for half a turn. This is accomplished by scraping off the enamel coating on half of the circumference of the wire that makes contact with the electric power supply posts. Do this wrong and the motor will not turn. Place the the coil in its rack, connect the battery and give the coil a slight push to get it spinning. Watch the motor spin and be amazed. Hold a second magnet above the fixed one in the motor's base an record your observations (see the questions below). Be careful not to hit the rotating coil while holding the second magnet. |
Data, Calculations | There are no calculations. However, If your motor does not spin you will receive an "F". Every time you have to remake the coil, you grade will decline by one letter. The message: THINK carefully about how the motor woks before you scrape off the enamel to form contacts so that current can flow in the coil. |
Questions, Conclusions |
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Resources/Materials: | multimeter, various resistors, solderless breadboard, variable power supply |
Essential Question: How are properties like temperature, pressure, etc. actually measured? |
Using E&M Principles in Measuring Instruments
Describe the conditions needed to make a charged particle move in a spiral pattern inside a magnetic field.
Describe the hall effect. This effect is used in many forms of transducers (measuring devices) including magnetic field measuring devices.
Describe the effects of moving a conductor in a magnetic field.
Homefun (formative summative assessment): 17, 21, 25, 29, page 857-8
Essential Question: How can I make an "A" on the test? |
Chapter 29 Magnetics Review
Summative Assessment: Test on objectives 1-15
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Title | Investigation of Magnetic Fields with a Hall Effect Transducer |
Purpose | Measure various magnetic fields with a Hall effect transducer. |
Overview |
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Data, Calculations |
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Questions, Conclusions |
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Resources/Materials: | light bulb, computer system set up with Vernier LabPro software and Lab Pro units, variable power supply |
Formal Physics Investigation |
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Title | Measurement of the Mass to Charge ratio of an Electron |
Purpose | Measure the mass to charge ratio of an electron using a Lorentz Force Demonstrator (looks like a giant light bulb). |
Models | Various |
Overview | In the Lorentz Force Demonstrator a stream
of electrons are accelerated across a known voltage difference into a
magnetic field perpendicular to the electron stream so that the
electrons travel in a circular path. The magnetic field is provided by
a pair of coils as follows:
Measure the radius of the circulating electrons and calculate the charge to mass ratio of an electron. Have the teacher tilt the magnetic field so that it is no longer perpendicular to the electron's inlet velocity. Obsearver, record, and explain the effects as part of the lab write up. |
Safety Issues | Note: The equipment is extremely expensive and extremely fragile do not move it from the position where it was placed by the teacher. Be careful not to stumble over the extension cord. |
Equipment Limitations | The equipment is designed to operate for no more than an hour continuous. |
Resources/Materials: | Lorentz Force Demonstrator (looks like a giant light bulb). |
D. Magnetostatics (continued)................................................................20%
1. Forces on moving charges in magnetic fields
2. Forces on current-carrying wires in magnetic fields
3. Fields of long current-carrying wires
4. Biot-Savart and Ampere's law *
Sources of Magnetic Fields (Chap30 Serway)
Essential Question: Can the electric power lines interfere with the telephone transmissions through the wires hung on the same poles? |
Describe the magnetic field around a long thin current carrying wire.
Calculate the magnetic field around a long thin current carrying wire.
B = |
mo
I
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2pr |
- Where: I = current
- r = radial distance from the wire
- mo = permeability of free space
- current in same direction: wires pulled together
- current in opposite direction: wires pushed apart
dB = km I ds x (r-hat) / r^2
km = mo / 4p
- around a long thin current carrying wire (see objective 2)
- along the axis through the center of a current carrying loop
B =
mo I a22 (a2 + x2)3/2
- at the vertex of a current carrying arc of wire. Start with:
dB =
mo I (d q) 4pR
Relevance: Biot Savort law is the basis for many types of derivations and is the basis for 2 of the right hand thumb rules.
Solve for the conditions needed to levitate a current carrying wire above two other current carrying wires.
Solve for the forces on a rectangular current carrying loop of wire next to a long thin current carrying wire in the same plane as the loop.
Apply all three right hand thumb rules.
Homefun (formative summative assessment): problems 10 (will be formally graded), 1, 3, 5, 17 p.859-860
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Title | Investigation of "Twiddler's Delight" |
Purpose | Determine the mechanism that accounts for the behavior of the "Twiddler's Delight" |
Overview |
A Twiddler's Delight looks like a cylinder with a movable shaft protruding from each
end. Twist one shaft and something happens to the other.
Start by simply playing with the Twiddler's Delight and developing a hypothesis for how the device works. Next devise a simple experiments to test your hypothesis. Briefly record your procedure, what you observed, and what you learned from each experiment The rules are that you can do nothing invasive. For example, you can't remove parts, drill holes, or in any way disect or modify the device. |
Data, Calculations | See above. |
Questions, Conclusions | Record you conclusion about how the device works. |
Resources/Materials: | "Twiddler's Delights" |