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Chapter 33. The Magnetic Field

Chapter 33. The Magnetic Field. Digital information is stored on a hard disk as microscopic patches of magnetism. Just what is magnetism? How are magnetic fields created? What are their properties? These are the questions we will address.

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Chapter 33. The Magnetic Field

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  1. Chapter 33. The Magnetic Field Digital information is stored on a hard disk as microscopic patches of magnetism. Just what is magnetism? How are magnetic fields created? What are their properties? These are the questions we will address. Chapter Goal: To learn how to calculate and use the magnetic field.

  2. Chapter 33. The Magnetic Field Topics: • Magnetism • The Discovery of the Magnetic Field • The Source of the Magnetic Field: Moving Charges • The Magnetic Field of a Current • Magnetic Dipoles • Ampère’s Law and Solenoids • The Magnetic Force on a Moving Charge • Magnetic Forces on Current-Carrying Wires • Forces and Torques on Current Loops • Magnetic Properties of Matter

  3. Stop to think 33.1 page 1000 Stop to think 33.2 page 1002 Stop to think 33.3 page 1005 Stop to think 33.4 page 1012 Stop to think 33.5 page 1021 Stop to think 33.6 page 1028 Stop to think 33.7 page 1031

  4. Tactics: Right-hand rule for fields

  5. The Source of the Magnetic Field: Moving Charges The magnetic field of a charged particle q moving with velocity v is given by the Biot-Savart law: where r is the distance from the charge and θ is the angle between v and r. μ0 is permeability constant =4π×10-7 Tm/A The Biot-Savart law can be written in terms of the cross product as

  6. The Magnetic Field of a Current The magnetic field of a long, straight wire carrying current I, at a distance d from the wire is See textbook P1007 The magnetic field at the center of a coil of N turns and radius R, carrying a current I is See textbook P1008

  7. The strength of the uniform magnetic field inside a solenoid is where n = N/l is the number of turns per unit length.

  8. EXAMPLE 33.4 The magnetic field strength near a heater wire QUESTION:

  9. EXAMPLE 33.4 The magnetic field strength near a heater wire

  10. Magnetic Dipoles The magnetic dipole moment of a current loop enclosing an area A is defined as The SI units of the magnetic dipole moment are A m2. The on-axis field of a magnetic dipole is See textbook P1011

  11. The Magnetic Force on a Moving Charge The magnetic force on a charge q as it moves through a magnetic field B with velocity v is where α is the angle between v and B.

  12. Magnetic forces on moving charges

  13. Cyclotron motion e

  14. Force between two parallel wires

  15. Is magnetic dipole moments

  16. What is the current direction in the loop? • Out of the page at the top of the loop, into the page at the bottom. • Out of the page at the bottom of the loop, into the page at the top.

  17. An electron moves perpendicular to a magnetic field. What is the direction of B • Left • Into the page • Out of the page • Up • Down

  18. What is the current direction in this loop? And which side of the loop is the north pole? • Current counterclockwise, north pole on bottom • Current clockwise; north pole on bottom • Current counterclockwise, north pole on top • Current clockwise; north pole on top

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