Reading Quiz

1. Reading Quiz • 2. What is the shape of the trajectory that a charged particle follows in a uniform magnetic field? • Helix • Parabola • Circle • Ellipse • Hyperbola • What is the SI unit for the strength of the magnetic field? • Gauss • Henry • Tesla • Becquerel • Bohr magneton

2. Reading Quiz • 4. The magnetic field of a straight, current-carrying wire is • parallel to the wire. • inside the wire. • perpendicular to the wire. • around the wire. • zero. • 3. The magnetic field of a point charge is given by • Biot-Savart’s law. • Faraday’s law. • Gauss’s law. • Ampère’s law. • Einstein’s law.

3. What is the SI unit for the strength of the magnetic field? • Gauss • Henry • Tesla • Becquerel • Bohr magneton

4. What is the shape of the trajectory that a charged particle follows in a uniform magnetic field? • Helix • Parabola • Circle • Ellipse • Hyperbola

5. The magnetic field of a point charge is given by • Biot-Savart’s law. • Faraday’s law. • Gauss’s law. • Ampère’s law. • Einstein’s law.

6. The magnetic field of a straight, current-carrying wire is • parallel to the wire. • inside the wire. • perpendicular to the wire. • around the wire. • zero.

7. Field Around Magnet • Use a compass to map the direction of the magnetic field surrounding a magnet. • White board your results. In particular: • how does the strength of the field vary with distance from the wire? • how does the field direction relate to the poles of the magnet? Magnetism

8. Activity: Map Field of Magnets • Use iron filings to map the field of a • bar magnet • horseshoe magnet • White board results • draw field lines. • how might magnets generate magnetic fields? Magnetism

9. Magnetic Field Lines • direction of magnetic field, B, is parallel to field line • number of lines per area is proportional to strength of field • field lines point • from N to S • field lines formclosed loops Magnetism

10. Magnetism No magnetic monopoles! Magnetism

11. Magnets are similar to Electric Dipoles Magnetism

12. Ferromagnetism • Ferromagnetic material • iron or other materials that can be made into magnets • You can make a magnet from iron by placing it in a strong B field • individual domains become aligned with external B field • Loss of magnetism from: • dropping • heating • Curie temperature • 1043 K for iron Preferentially downwards Random Magnetism

13. Cross Product – Right Hand Rule Magnetism

14. Specifying 3 Dimensions • out of page • tip of arrow • into page • tail of arrow Magnetism

15. Force on a moving charge • Right Hand Rule (#2) • qv = fingers • B = bend fingers • F = thumb • Find the direction of the force on a negative charge for each diagram shown. Magnetism

16. Magnetism

17. Think-Pair-Share • Derive an expression for the radius of an e-’s orbit in a uniform B field. Express your answer in terms of me, v, qe, and B. Turn in your solution! Magnetism

18. Earth’s Magnetic Field • magnetic declination • angular difference between geographic north and magnetic north • varies with latitude Magnetism

21. Tactics: Right-hand rule for fields

22. 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. The Biot-Savart law can be written in terms of the cross product as

23. EXAMPLE 33.1 The magnetic field of a proton QUESTION:

24. EXAMPLE 33.1 The magnetic field of a proton

25. EXAMPLE 33.1 The magnetic field of a proton

26. EXAMPLE 33.1 The magnetic field of a proton

27. 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 The magnetic field at the center of a coil of N turns and radius R, carrying a current I is

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

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

30. Practice Problems • Magnetism: Worksheets 1 and 2 • Finish before next class Magnetism

32. Tactics: Finding the magnetic field direction of a current loop

33. 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

34. EXAMPLE 33.7 The field of a magnetic dipole QUESTIONS:

35. EXAMPLE 33.7 The field of a magnetic dipole

36. Tactics: Evaluating line integrals

37. Ampère’s law Whenever total current Ithrough passes through an area bounded by a closed curve, the line integral of the magnetic field around the curve is given by Ampère’s law:

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

39. 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.

41. Magnetic Forces on Current-Carrying Wires Consider a segment of wire of length l carrying current I in the direction of the vector l. The wire exists in a constant magnetic field B. The magnetic force on the wire is where α is the angle between the direction of the current and the magnetic field.

42. EXAMPLE 33.13 Magnetic Levitation QUESTION:

43. EXAMPLE 33.13 Magnetic Levitation

45. General Principles

46. General Principles

47. General Principles

48. Applications

49. Applications

50. Applications