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.

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Reading Quiz

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Reading quiz

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

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.


Reading quiz

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

  • Gauss

  • Henry

  • Tesla

  • Becquerel

  • Bohr magneton


Reading quiz

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

  • Helix

  • Parabola

  • Circle

  • Ellipse

  • Hyperbola


Reading quiz

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.


Reading quiz

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

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

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

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

Magnetism

No magnetic monopoles!

Magnetism


Magnets are similar to electric dipoles

Magnets are similar to Electric Dipoles

Magnetism


Ferromagnetism

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

Cross Product – Right Hand Rule

Magnetism


Specifying 3 dimensions

Specifying 3 Dimensions

  • out of page

  • tip of arrow

  • into page

  • tail of arrow

Magnetism


Force on a moving charge

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


Reading quiz

Magnetism


Think pair share

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

Earth’s Magnetic Field

  • magnetic declination

    • angular difference between geographic north and magnetic north

    • varies with latitude

Magnetism


Tactics right hand rule for fields

Tactics: Right-hand rule for fields


The source of the magnetic field moving charges

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

EXAMPLE 33.1 The magnetic field of a proton

QUESTION:


Example 33 1 the magnetic field of a proton1

EXAMPLE 33.1 The magnetic field of a proton


Example 33 1 the magnetic field of a proton2

EXAMPLE 33.1 The magnetic field of a proton


Example 33 1 the magnetic field of a proton3

EXAMPLE 33.1 The magnetic field of a proton


The magnetic field of a current

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

EXAMPLE 33.4 The magnetic field strength near a heater wire

QUESTION:


Example 33 4 the magnetic field strength near a heater wire1

EXAMPLE 33.4 The magnetic field strength near a heater wire


Practice problems

Practice Problems

  • Magnetism: Worksheets 1 and 2

  • Finish before next class

Magnetism


Tactics finding the magnetic field direction of a current loop

Tactics: Finding the magnetic field direction of a current loop


Magnetic dipoles

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

EXAMPLE 33.7 The field of a magnetic dipole

QUESTIONS:


Example 33 7 the field of a magnetic dipole1

EXAMPLE 33.7 The field of a magnetic dipole


Tactics evaluating line integrals

Tactics: Evaluating line integrals


Amp re s law

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:


Reading quiz

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 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

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

EXAMPLE 33.13 Magnetic Levitation

QUESTION:


Example 33 13 magnetic levitation1

EXAMPLE 33.13 Magnetic Levitation


General principles

General Principles


General principles1

General Principles


General principles2

General Principles


Applications

Applications


Applications1

Applications


Applications2

Applications


Reading quiz

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

  • Clockwise

  • Counterclockwise

  • Not at all


Reading quiz

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

  • Clockwise

  • Counterclockwise

  • Not at all


Reading quiz

The magnetic field at the position P points

  • Into the page.

  • Up.

  • Down.

  • Out of the page.


Reading quiz

The magnetic field at the position P points

  • Into the page.

  • Up.

  • Down.

  • Out of the page.


Reading quiz

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


Reading quiz

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


Reading quiz

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


Reading quiz

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


Reading quiz

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

  • Left

  • Into the page

  • Out of the page

  • Up

  • Down


Reading quiz

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

  • Left

  • Into the page

  • Out of the page

  • Up

  • Down


Reading quiz

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.


Reading quiz

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.


Reading quiz

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


Reading quiz

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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