![Page 1: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/1.jpg)
BoardWork
Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)
![Page 2: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/2.jpg)
Magnets and Currents
interacting and inseparable
![Page 3: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/3.jpg)
Objectives
• Describe the magnetic field caused by an electrical current.
• Determine the force on an electric charge in a magnetic field.
![Page 4: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/4.jpg)
What’s the Point?
• What is the force that underlies electric motors?
![Page 5: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/5.jpg)
Current Creates Magnetism
An electric current creates a magnetic field.
Look, Ma! No poles!
![Page 6: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/6.jpg)
Vector Direction Conventions
Up Down
In Out
RightLeft
![Page 7: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/7.jpg)
Poll Question
If a wire in front of you carries a current from left to right, what is the direction of the resulting magnetic field where you are?
I
A. B. C.
D. E. F.
![Page 8: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/8.jpg)
Board Work
An electric current creates a magnetic field whose lines circle right-handed around it. Draw lines for the magnetic field created by a ring of current.
I
![Page 9: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/9.jpg)
Magnetic Field of Current Ring
Source: Griffith, The Physics of Everyday Phenomena
N
S
dipole field
![Page 10: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/10.jpg)
Solenoid Magnetic Field
Source: Griffith, The Physics of Everyday Phenomena
N S
![Page 11: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/11.jpg)
Electrons are Magnets!
spin
![Page 12: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/12.jpg)
Electrons are Magnets!
current
![Page 13: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/13.jpg)
Electrons are Magnets!
magnetic field
![Page 14: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/14.jpg)
Electrons are Magnets!
N
S
magnetic dipole
![Page 15: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/15.jpg)
Types of Magnets
• Electromagnets– currents travel through conducting coils
• Permanent Magnets– materials whose electrons have aligned spins
or orbits
Moving charges create the fields!
![Page 16: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/16.jpg)
The Lorentz Force
making electrons work for us
![Page 17: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/17.jpg)
Magnetic Force on a Charge
• Currents create magnetic fields.
• Currents are made of moving charges.
• Moving charges are magnets.
• Magnets apply forces to each other.
• Magnets apply forces to moving charges.
How do those forces behave?
![Page 18: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/18.jpg)
Lorentz Force
Right-Hand Rule
F = qv B
Source: Griffith, The Physics of Everyday Phenomena
qv
![Page 19: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/19.jpg)
Poll Question
What is the direction of the cross product A B?
A
B
A.
B.
C.
D.
E.
F.
![Page 20: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/20.jpg)
Cross Product Review
A
B
a
b
AB = area of parallelogram
![Page 21: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/21.jpg)
Cross Product Review
• Curl right-hand fingers in direction of
• Right-hand thumb points in direction of cross-product
• Not commutative
A
B
a
b
AB = –(BA)
![Page 22: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/22.jpg)
Lorentz Force Properties
• F = 0 unless charge is moving
• F = 0 if velocity is to field
• F = maximum if velocity is to field
• F 0 only if charge crosses B field lines
• If q, v or B reverse, direction of F reverses
![Page 23: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/23.jpg)
paper square
Make an Origami Right Hand
fold over
magnetic
fieldcurrent
qv
For
ce
Lore
ntz
vectors
creases:in out
![Page 24: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/24.jpg)
Think Question
What is the direction of the force on the object moving with velocity v through magnetic field B?
B
v
+
A.
B.
C.
D.
E.
F.
![Page 25: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/25.jpg)
B
Group Poll Question
What is the magnitude of the force on object A compared to the magnitude of the force on object B?
v
q
v
2qA BA. FB = 4 FA
B. FB = 2 FA
C. FB = FA
D. FB = FA/2
E. FB = FA/4
![Page 26: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/26.jpg)
B
Group Poll Question
How does the work done on object A compare to the work done on object B?
v
q
v
2qA B
A. wB > wA.
B. wB = wA.
C. wB < wA.
![Page 27: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/27.jpg)
Lorentz and Newton’s third law
• F = qv B does not explicitly include a reaction force.
• Magnetic fields (B) are always created by moving charges.
• Moving charges (qv) always create magnetic fields.
• The moving charge creating B “feels” the field of qv. So F = qv B goes both ways.
Here’s where it is:
![Page 28: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/28.jpg)
Board Work
From F = qv × B, find the SI unit of magnetic field B.
![Page 29: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/29.jpg)
Challenge Question
A current runs through one wire of a pair of parallel wires. What is the direction of the resulting magnetic field at the location of the other wire?
I
??
![Page 30: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/30.jpg)
Force between parallel currents
What is the force on this current?I B
![Page 31: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/31.jpg)
Definition of Ampere
• If two parallel wires are held 1 m apart,
• with currents of 1 A through each wire,
• the attractive force between the wires is 2 10–7 N for each meter of length of the wires.
![Page 32: BoardWork Indicate which pole of the magnet is north and which is south. (The blue lines represent magnetic field lines.)](https://reader036.vdocuments.net/reader036/viewer/2022062421/56649da55503460f94a906d6/html5/thumbnails/32.jpg)
Reading for Next Time
• Faraday’s law
• Big Ideas– A changing magnetic field can create an
electric potential– AC Transformers can be understood using
Faraday’s law and conservation of energy
• Very abstract– You are ready– It is very cool