ELECTRICITY AND MAGNETISM 

Go to: ELECTRIC FORCE, ELECTRIC FIELD, ELECTRIC POTENTIAL Go to: ELECTRIC CURRENT, POWER Go to: MAGNETISM AND ELECTROMAGNETISM Go to: AP FREE RESPONSE PROBLEMS


ELECTRIC FORCE, ELECTRIC FIELD, ELECTRIC POTENTIAL For problems involving Coulomb's Law: 1. Complete a data table with the information given. If more than two charged objects are given, draw a diagram showing the position of each object. 2. If the objects touch then charge transfer occurs and the law of conservation of charge must be applied to determine the charge on each object. 3. If more than two charges are given use the vector component method to solve the problem applying Coulomb's law. For problems involving the motion of a charged particle in an electric field: 1. Complete a data table with the information given. 2. Draw an accurate, labeled diagram showing the motion of the particle in the field. 3. Determine the magnitude and direction of the electric force acting on the particle. Use Newton's second law to determine the acceleration. For problems involving the magnitude and direction of the resultant electric field due to two or more point charges: 1. Complete a data table with the information given. 2. Draw an accurate, labeled diagram locating the position of each charge. 3. Determine the magnitude and direction of the electric field at the point in question due to each charge. 4. Use the vector component method to solve for the resultant electric field For the problems involving a charged particle accelerated through a potential difference: 1. Complete a data table with the information given. 2, Draw an accurate, labeled diagram showing the motion of the particle. 3. Use the concepts of electric field, electric force, and electric potential along with the concepts of workenergy theorem and/or Newton's second law to solve the problem. For problems involving the electric potential due to a point charge(s): 1. Complete a data table with the information given. 2. Solve for the potential due to each charge. The potential due to a negative charge is negative and for a positive charge the potential is positive. 3. The total potential equals the arithmetic sum of the potentials due to the individual point charges. 



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CAPACITORS For problems involving a parallel plate capacitor based on the physical characteristics of the capacitor: 1. Complete a data table with the information given and the value of the dielectric constant. 2. Determine the area of one plate and the distance between the plates. 3. Apply the formula for the capacitance of a parallel plate capacitor. For problems involving capacitance when a dielectric inserted after the initial conditions are described: 1. Complete a data table with the information given and the value of the dielectric constant. 2. If the battery is disconnected before the dielectric is inserted, the charge stored cannot increase. However, the magnitude of both the electric field and potential difference decrease. 3. If the battery remains connected, the charge stored increases. The magnitude of both the final electric field and the potential difference between the plates equals the value before the dielectric was inserted. 4. In each case, the final capacitance is greater than the original. For problems involving equivalent capacitance: 1. Determine whether the capacitors are arranged in series or in parallel. 2. If necessary, simplify the circuit step by step until it is reduced to a simple series or parallel combination. Use the appropriate formula to determine the equivalent capacitance. 3. Solve for the charge stored on each capacitor and the potential difference across each capacitor. 



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ELECTRIC CURRENT and POWER For problems involving resistivity and temperature coefficient of resistance: 1. Complete a data table with the information given. 2. Solve for the resistance at some higher temperature. For problems involving electric power, electric energy and the cost of electric energy: 1. Complete a data table with the information given. 2. Determine the power dissipated in watts and kilowatts. 3. Determine the number of kWhr of energy used and multiply the number of kWhr by the cost per kWhr 



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DC CIRCUITS For problems involving equivalent resistance: 1. Determine whether the resistors are arranged in series or in parallel. 2. If necessary, simplify the circuit step by step until it is reduced to a simple series or parallel combination. Use the appropriate formula to determine the equivalent resistance. 3. Use Ohm's law and Kirchhoffs' laws to solve for the current through each resistor and the potential difference across each resistor. For problems involving a complex circuit (Kirchhoff's Laws): 1. Assign a direction to the current in each branch of the circuit. Place a positive sign on the side of each resistor where the current enters and a negative sign where the current exits. 2. Place a positive sign at the positive terminal of each battery and a negative sign at the negative terminal. 3. Select a junction point and use Kirchhoff's junction rule to write an equation for the currents entering the point. 4. Apply Kirchhoff's loop rule and write equations based on the gains and losses of potential around selected loops. 5. Solve the equations for the unknown currents algebraically. 



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MAGNETISM AND ELECTROMAGNETISM For problems involving a currentcarrying wire in a magnetic field: 1. Complete a data table with the information given. 2. Draw an accurate labeled diagram showing the orientation of the wire in the magnetic field. Use the adopted conventions to indicate the direction of the current and the magnetic field. 3. Use the righthand rule to determine the direction of the force on the wire. 4. Determine the magnitude of the force. For problems involving a charged particle traveling through a magnetic field: 1. Complete a data table with the information given. 2. Draw an accurate labeled diagram showing the motion of the particle through the magnetic field. Use the adopted conventions to indicate the direction of the magnetic field and the direction of motion of the particle. 3. Take note of whether the particle is positively charged or negatively charged and then use the righthand rule to determine the direction of the force on the particle. 4. If the particle is deflected into circular motion, the magnetic force produces a centripetal acceleration. Use Newton's second law to determine the acceleration. 5. If the speed of the particle as it enters the magnetic field is given or can be calculated, it is possible to determine the radius of circle in which the particle travels. For problems involving the magnetic field produced by a currentcarrying wire: 1. Complete a data table with the information given. 2. Draw a diagram showing the orientation of the straight wire or the loop of wire and the direction of the current in the wire. 3. Use the second righthand rule to determine the direction of the magnetic field. Indicate the direction of the magnetic field. 4. Determine the magnitude of the magnetic field. For a straight wire moving at speed v through a uniform magnetic field: 1. Complete a data table with the information given. 2. Determine the magnitude of the induced emf. 3. If the wire is part of a closed circuit, use Ohm's law to determine the current through the wire and then determine the force which opposes the mechanical force acting on the wire. For problems involving a changing magnetic flux through a loop of wire: 1. Complete a data table with the information given. 2. Determine the rate of change of flux. 3. Apply Faraday's law to determine the magnitude of the induced emf. 4. Apply Ohm's law to determine the magnitude of the induced current and Lenz's law to determine its direction. For problems involving transformers: 1. Complete a data table with the information given. 2. Use the transformer equation that relates the voltage and number of turns in the primary to the voltage and number of turns in the secondary. 3. An ideal transformer is 100% efficient. The power in the primary equals the power in the secondary. Use this concept to solve for the current in the secondary. 



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ELECTRICITY AND MAGNETISM FREE RESPONSE AP PROBLEMS The list of problems is given as follows: Year of examination Problem number Topics covered in problem 1983, 3, DC circuit, Ohm's law, Kirchhoff's law, power 1984, 4, forces on a moving charge in a magnetic field 1985, 3, forces on a moving charge in an electric field between two plates 1986, 3, DC circuit, Ohm's law 1986, 4, forces on a moving loop of wire in a magnetic field, power 1987, 2, Coulomb's law, electric field 1987, 4, DC circuit, Ohm's law, power 1989, 2, Coulomb's law, electric field and potential 1989, 3, DC circuit, Ohm's law 1990, 2, forces on a moving charge in an electric field between two plates, kinematics and magnetic field 1990, 3, DC circuit, Ohm's law, power 1991, 2, forces on a moving charge in a magnetic field 1991, 4, DC circuit, Ohm's law 1992, 3, Ohm's law, calorimetry, power 1992, 5, forces on a moving charge in a magnetic field and an electric field 1994, 4, forces on a moving charge in a magnetic field, power, potential difference 1994, 6, conducting bar moving perpendicular to a magnetic field, force on a current carrying wire, power, Lenz's law 1995, 2, DC circuit, Ohm's law, power 1995, 7, force on a moving charge in a magnetic field 1996, 4, DC circuit, Ohm's law, power 1996, 6, Millikan's oil drop experiment 1997, 3, parts b, c) force on a current carrying wire in a magnetic field, Ohm's law 1997, 4, DC circuit, calorimetry, power 2000, 3, circuit with resistors and a capacitor, Ohm's law, electric field, potential difference, capacitance 2000,7, forces on a moving charge in a magnetic field and an electric field 2001, 3, electric potential and electric field 2001, 5, experiment design using resistance and temperature values 



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