White board your results. In particular: 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? General Physics 2 Magnetism

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? General Physics 2 Magnetism

direction of magnetic field, B, is parallel to field line 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 form closed loops General Physics 2 Magnetism

Magnetism No magnetic monopoles! General Physics 2 Magnetism

Magnets are similar to Electric Dipoles General Physics 2 Magnetism

Ferromagnetism Ferromagnetic material Preferentially Random downwards 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 General Physics 2 Magnetism

Cross Product – Right Hand Rule General Physics 2 Magnetism

Specifying 3 Dimensions out of page tip of arrow into page tail of arrow General Physics 2 Magnetism

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. General Physics 2 Magnetism

General Physics 2 Magnetism

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! Start of class 2 - students have already completed worksheets 1 & 2 General Physics 2 Magnetism

Earth’s Magnetic Field magnetic declination angular difference between geographic north and magnetic north varies with latitude General Physics 2 Magnetism

Tactics: Right-hand rule for fields

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

EXAMPLE 33.1 The magnetic field of a proton QUESTION:

EXAMPLE 33.1 The magnetic field of a proton

EXAMPLE 33.1 The magnetic field of a proton

EXAMPLE 33.1 The magnetic field of a proton

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

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

EXAMPLE 33.4 The magnetic field strength near a heater wire

Magnetism: Worksheets 1 and 2 Finish before next class Practice Problems Magnetism: Worksheets 1 and 2 Finish before next class General Physics 2 Magnetism

Tactics: Finding the magnetic field direction of a current loop

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

EXAMPLE 33.7 The field of a magnetic dipole QUESTIONS:

EXAMPLE 33.7 The field of a magnetic dipole

Tactics: Evaluating line integrals

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:

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

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.

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.

EXAMPLE 33.13 Magnetic Levitation QUESTION:

EXAMPLE 33.13 Magnetic Levitation

General Principles

General Principles

General Principles

Applications

Applications

Applications

Does the compass needle rotate clockwise (cw), counterclockwise (ccw) or not at all? STT32.1 Answer: C

Does the compass needle rotate clockwise (cw), counterclockwise (ccw) or not at all? STT32.1

The magnetic field at the position P points Into the page. Up. Down. Out of the page. STT32.2 Answer: D

The magnetic field at the position P points Into the page. Up. Down. Out of the page. STT32.2

The positive charge is moving straight out of the page The positive charge is moving straight out of the page. What is the direction of the magnetic field at the position of the dot? Left Right Down Up STT32.3 Answer: C

The positive charge is moving straight out of the page The positive charge is moving straight out of the page. What is the direction of the magnetic field at the position of the dot? Left Right Down Up STT32.3

What is the current direction in this loop 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 STT32.4 Answer: B

What is the current direction in this loop 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 STT32.4

An electron moves perpendicular to a magnetic field An electron moves perpendicular to a magnetic field. What is the direction of ? Left Into the page Out of the page Up Down STT32.5 Answer: B

An electron moves perpendicular to a magnetic field An electron moves perpendicular to a magnetic field. What is the direction of ? Left Into the page Out of the page Up Down STT32.5

What is the current direction in the loop? STT32.6 Answer: B 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.

What is the current direction in the loop? STT32.6 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.

Which magnet or magnets produced this induced magnetic dipole? a or d a or c b or d b or c any of a, b, c or d STT32.7 Answer: B

Which magnet or magnets produced this induced magnetic dipole? a or d a or c b or d b or c any of a, b, c or d STT32.7