Physics C Electricity and Magnetism

Unit 5: Magnetism

Big Ideas:
1. The source of a magnetic field is a moving charge.
2. Current carrying conductors can exert force on each other.

1. Students should understand the force experienced by a charged particle in a magnetic field, so they can:
A. Calculate the magnitude and direction of the force in terms of q, v, and, B, and explain why the magnetic force can perform no work.
B. Deduce the direction of a magnetic field from information about the forces experienced by charged particles moving through that field.
C. Describe the paths of charged particles moving in uniform magnetic fields.
D. Derive and apply the formula for the radius of the circular path of a charge that moves perpendicular to a uniform magnetic field.
E. Describe under what conditions particles will move with constant velocity through crossed electric and magnetic fields.

2. Students should understand the force exerted on a current-carrying wire in a magnetic field, so they can:
A. Calculate the magnitude and direction of the force on a straight segment of current-carrying wire in a uniform magnetic field.
B. Indicate the direction of magnetic forces on a current-carrying loop of wire in a magnetic field, and determine how the loop will tend to rotate as a consequence of these forces.
C. Calculate the magnitude and direction of the torque experienced by a rectangular loop of wire carrying a current in a magnetic field.

3. Students should understand the magnetic field produced by a long straight current-carrying wire, so they can:
A. Calculate the magnitude and direction of the field at a point in the vicinity of such a wire.
B. Use superposition to determine the magnetic field produced by two long wires.
C. Calculate the force of attraction or repulsion between two long current-carrying wires.

4. Students should understand the Biot-Savart Law, so they can:
A. Deduce the magnitude and direction of the contribution to the magnetic field made by a short straight segment of current-carrying wire.
B. Derive and apply the expression for the magnitude of B on the axis of a circular loop of current.

5. Students should understand the statement and application of Ampere’s Law in integral form, so they can:
A. State the law precisely.
B. Use Ampere’s law, plus symmetry arguments and the right-hand rule, to relate magnetic field strength to current for planar or cylindrical symmetries.
C. Students should be able to apply the superposition principle so they can determine the magnetic field produced by combinations of the configurations listed above.

6. Students should understand the concept of magnetic flux, so they can:
A. Calculate the flux of a uniform magnetic field through a loop of arbitrary orientation.
B. Use integration to calculate the flux of a non-uniform magnetic field, whose magnitude is a function of one coordinate, through a rectangular loop perpendicular to the field.

7. Students should understand Faraday’s law and Lenz’s law, so they can:
A. Recognize situations in which changing flux through a loop will cause an induced emf or current in the loop.
B. Calculate the magnitude and direction of the induced emf and current in a loop of wire or a conducting bar when the magnitude of a related quantity such as magnetic field or area of the loop is changing at a constant rate or when the magnitude of a related quantity such as magnetic field or area of the loop is a specified non-linear function of time.

8. Students should be able to analyze the forces that act on induced currents so they can determine the mechanical consequences of those forces.