Chapter 28

Sources of Magnetic Field

Our approach• B due to a straight wire

• Force between two straight parallel current carrying wires

• The modern def. of Ampere and Coulomb

• Ampere’s Law– Applications and rln to Gauss’ Law

• Biot-Savart Law

• Magnetic materials

• Exploration of B produced by a solenoid

Magnetic Field Due to Straight Wires

• On what does the magnitude of the magnetic field created by a current in a straight wire depend?

• What exactly is the magnitude of the magnetic field around a straight wire with a current?

• How is the magnetic field among parallel wires with currents calculated?

Force between two current- carrying wires

• How can one derive the force between two parallel wires carrying currents?

• What is the force’s dependence on the distance between the wires? And how does this make sense?

• In general, when do parallel wires with currents attract or repel each other?

Definition of the Ampere and the Coulomb

• How are the Ampere and Coulomb defined in terms of the magnetic interaction?

Ampere’s Law

• In general, what two things does Ampere’s Law relate?

• What precisely is Ampere’s Law?

• In general, in what situations is Ampere’s Law most useful?

• How is symmetry used to define the “Amperian” path?

Ampere’s Law (cont’d)

• Compare Ampere’s Law and Gauss’s Law.

• Use Ampere’s Law to calculate the magnetic field inside a solenoid?

• Use Ampere’s Law to calculate the magnetic field inside a toroid?

Biot-Savart Law

• How does the Biot-Savart Law allow calculation of a magnetic field from current when there is insufficient symmetry to use Ampere’s Law?

• What is the Biot-Savart Law?

• Use the Biot-savart Law to calculate B along the axis of symmetry of a current loop and from a wire segment.

Magnetic Materials

• What is the basis of ferromagnetism?

• What are magnetic domains?

• How is un-magnetized iron attracted by magnets?

• How can ferromagnetism be created and destroyed?

• What is the Curie temperature?

Magnetic Materials (cont’d)

• How do paramagnetic and diamagnetic materials behave as compared to ferromagnetic materials?

• What is the basis of paramagnetism?

• What is the basis of diamagnetism?

(We will skip the very interesting subject of hysteresis.)

The end