Download Power point - Physics 420 UBC Physics Demonstrations

Electromagnetism
University of British Columbia
Physics 420
By: Jason Cheung
What is a Field?
• A region of space characterized by a
physical property having a determinable
value at every point in the region
• Examples: gravitational field, Electric
field ,and magnetic field
Gravitational Field
• Defined as
A = acceleration
G = gravitational constant
r = distance to the center
of the big object
m = mass of big object
Electric Field
• Electric field is defined as the electric force
per unit Charge
E is measure in Force/Coulomb
E = Electric Field
F = Electric Force
q = Charge
• It is the surrounding charges that create
an electric field
Cathode Ray Tube Demo (CRT)
Magnetic Field
• Magnetic field is a field that exerts a force
on a moving charge
• A magnetic field can be caused either by
another moving charge or by a changing
of electric field or magnetic dipoles of
materials
• Magnetic Field is measure in Tesla
A simple formula to calculate Magnetic Field
B=
F=
Q=
V=
magnetic field
Magnetic Force
charge
velocity of the moving charge
Battery Demo
• Charge moving in a magnetic field obeys
the Right Hand Rule
• There are two types of RHR
– Right Hand Rule #1
– Right Hand Rule #2
Right Hand Rule 1
• The thumb represents the velocity of
which the charge is going
• The remaining fingers tell you the
direction of the magnetic field
• example:
Right Hand Rule 2
• I = direction of the charge
• B = direction of the Magnetic Field
• F = Force act on the charge
– Palm Push Positive (*Remember!!)
Right Hand Rule Question
Magnetism
What is magnetism?
Magnetism is one of the phenomena by which
materials exert an attractive or repulsive force
on other materials.
What causes magnetism in material?
It is the unpaired electrons in the electron
orbit cause magnetism
example of pair and unpaired:
N is unpaired,
O is paired (one of them)
Remember SPDF?? (Chem 11)
• Electrons fall into electron shell according
to Hund’s rule.
– Examples
Nitrogen
-Electrons
-Protons and Neutrons
1s2
2s2
2p3
Right
Electron
Configuration
of
Wrong
Nitrogen
Wrong
There are four types of magnetism
1.Ferromagnetic
2.Paramagnetic
3.Diamagnetic
4.Ferrimagnetic
(Not going to cover)
Magnetism is Measure in Magnetic Susceptibility (χm)
Material
Susceptibility χm
Vacuum
Water
Bi
C
O2
Al
Fe
Co
Ni
0
-1.2*10-5
-16.6*10-5
-2.1*10-5
0.19*10-5
2.2*10-5
200
70
110
The more susceptibility
of a material has,
the more magnetic
property
it processes
Ferromagnetic
• Any material that possess magnetization
WITHOUT an external magnetic field is
ferromagnetic
• large and positive susceptibility
• Examples of ferromagnetic materials
Iron (Fe)
Cobalt (Co)
Susceptibility = 200
Susceptibility = 70
Iron electron configuration
Fe: 1s2,2s2,2p6,3s2,3p6,4s2,3d6
Ar: 1s2,2s2,2p6,3s2,3p6 = [Ar] “Core”
Fe: [Ar],4s2,3d6
[Ar]
-The electrons seems to align spontaneously
-Pure quantum mechanics effect
Why are some Ferromagnetic
doesn’t attract one another?
• Has to do with the magnetic domain of
the material
Ferromagnetic material demo
Paramagnetic
• Any material that possess magnetization (i.e.
attraction with other magnetized material) WITH
an external magnetic field is paramagnetic
• small and positive susceptibility
• Examples of paramagnetic materials
Aluminum Al
Susceptibility = 2.2*10-5
Platinum Pt
Aluminum electron configuration
[Ne].3s2.3p1
What is the differences between the two?!
Compare to Iron (Fe)
[Ar]
Fe: [Ar],4s2,3d6
the dipoles do not interact with one another and are randomly oriented in
the absence of an external field due to thermal agitation,
resulting in zero net magnetic moment
Paramagnetic and Ferromagnetic
Demo (magnets and levitation)
Diamagnetic
• very weak and negative susceptibility to
magnetic fields.
• Negative susceptibility = repel against
magnetic fields (diamagnetism)
• Positive susceptibility = attract to
magnetic fields (para + ferromagnetism)
Diamagnetism
• Examples of diamagnetic materials
Gold
Human (mostly)
Copper
Diamagnetic Levitation Demo
Applications of Magnetism
MRI (magnetic resonance images)
Superconductors
Applications of Magnetism
• Maglev Trains