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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. Reading Quiz.

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Reading Quiz

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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


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.


What is the SI unit for the strength of the magnetic field?

  • Gauss

  • Henry

  • Tesla

  • Becquerel

  • Bohr magneton


What is the shape of the trajectory that a charged particle follows in a uniform magnetic field?

  • Helix

  • Parabola

  • Circle

  • Ellipse

  • Hyperbola


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.


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.


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


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


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


Magnetism

No magnetic monopoles!

Magnetism


Magnets are similar to Electric Dipoles

Magnetism


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


Cross Product – Right Hand Rule

Magnetism


Specifying 3 Dimensions

  • out of page

  • tip of arrow

  • into page

  • tail of arrow

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.

Magnetism


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!

Magnetism


Earth’s Magnetic Field

  • magnetic declination

    • angular difference between geographic north and magnetic north

    • varies with latitude

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


Practice Problems

  • Magnetism: Worksheets 1 and 2

  • Finish before next class

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?

  • Clockwise

  • Counterclockwise

  • Not at all


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

  • Clockwise

  • Counterclockwise

  • Not at all


The magnetic field at the position P points

  • Into the page.

  • Up.

  • Down.

  • Out of the page.


The magnetic field at the position P points

  • Into the page.

  • Up.

  • Down.

  • 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


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


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


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


An electron moves perpendicular to a magnetic field. What is the direction of ?

  • Left

  • Into the page

  • Out of the page

  • Up

  • Down


An electron moves perpendicular to a magnetic field. What is the direction of ?

  • Left

  • Into the page

  • Out of the page

  • Up

  • Down


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.


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.


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


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


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