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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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slide1

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
slide2

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.
slide4

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

  • Helix
  • Parabola
  • Circle
  • Ellipse
  • Hyperbola
slide5

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.
slide6

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

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

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

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

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

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

practice problems
Practice Problems
  • Magnetism: Worksheets 1 and 2
  • Finish before next class

Magnetism

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

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:

slide38

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.

slide51

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

  • Clockwise
  • Counterclockwise
  • Not at all
slide52

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

  • Clockwise
  • Counterclockwise
  • Not at all
slide53

The magnetic field at the position P points

  • Into the page.
  • Up.
  • Down.
  • Out of the page.
slide54

The magnetic field at the position P points

  • Into the page.
  • Up.
  • Down.
  • Out of the page.
slide55

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
slide56

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
slide57

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
slide58

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
slide59

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

  • Left
  • Into the page
  • Out of the page
  • Up
  • Down
slide60

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

  • Left
  • Into the page
  • Out of the page
  • Up
  • Down
slide61

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.
slide62

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.
slide63

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
slide64

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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