Download Power point - Physics 420 UBC Physics Demonstrations

Legend
-White background is for
Teacher to see as instructions.
-Blue back ground is for the
Student to see
• My presentation is more gear toward
upper level high school physics student
(i.e. Physics 11, Physics 12 and Physics 12
AP).
Materials needed for the
demonstrations
Materials needed for the construction of the demos
• Pliers
• Sand paper
• Glue gun
Materials needed for the demos. Instructions will be given in later slides
#1 Cathode ray tube demo
• Cathode ray tube set
#3 Ferromagnetic levitation
• borrow a levitation device from a year 2
Mechanical Engineering 2006 friend
#2 Battery demo
• 9V battery
• thin copper wires
• rubber band
• a neodymium magnet
(order online @ www.grand-illusions.com/toyshop or ebay)
#4 Diamagnetic levitation
• 4 neodymium magnets
• a piece of pyrolytic carbon
#5 Maglev train
• Strong magnetic strips
• thin plexiglass
• the support track
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
Explanation of Field (#1)
(for slide 5)
•
This means if we put anything appropriate in a field, we can then calculate “something” out of
that field
•
Before going further with Electric field and Magnetic field, mention there are something called the
Electric and Magnetic field. Use gravitational field as a start, because G-field the most easy to
understand
•
Link Electric field and Magnetic field after explaining the Gravitational field
Gravitational Field
• Defined as
A = acceleration
G = gravitational constant
r = distance to the center
of the big object
m = mass of big object
Explanation of Field (#2)
(for slide 8)
•
If we put Bob in the gravitational field, we can calculate the Force acting on him by the Earth. He
will follow the gravitational field lines and fall to the surface of the Earth.
•
Essentially, if we put anything that has a mass in the Gravitational field, we can calculate that
“something” I mentioned before. That “something” is the “gravitational force” in this case.
•
Emphasize that we determine different kinds of force with different kinds of field. This can
bridge to Electric and Magnetic Field on following slides.
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
Explanation of Electric Field (E-field)
(for slide 10)
#0 Explain what is a charge, q
- They should have enough Physics to know what is a +/- charge is
- Opposite charges attract each other and Like charges repel each other
#1 Explain E is defined as F/q
- If we put a +/- (positive or negative) charge in a electric field, the +/- charge will
experience a force. This force is called “Electric Force”
- (IMPORTANT!!) Recall from G-field. G-field requires an object with a MASS to have a
force. E-field requires a +/- charge to have a force
#2 How do you draw the E-field lines with different charges?
- Electric field lines always comes out of the positive charge into the negative
charge
- Negative charge always absorb the E-field lines
Explanation of Electric Field (E-field)
(for slide 10)
#3 What direction is the electric force?
- The direction of the Electric force is parallel to the electric field.
- Look at the POINT P on the diagram on slide 10. The arrow in the diagram represents
the direction of the electric force
Q:
What is the charge, positive or negative, if the direction of the
force is pointing outward like in the diagram on slide 10
A:
Positive because it is point away from the stationary positive
charge
Q:
What is the charge, if the direction of the force on the diagram
switched??
A:
Negative charge
Cathode Ray Tube Demo (CRT)
Instruction and explanation for the CRT Demo
#1
Turn on the Power supply and Electric plate controller, and wait and calibrate the electrons to the
center of the screen
#2
Adjust the electric plate by turning the X knob or the Y knob. This is to demonstrate that the
electric plate can control where the electron will hit on the screen.
Questions and Fun facts
Q:
What do you think is the application of a CRT and what do the electric plates do in the CRT?
A:
Our “OLD” TV (before LCD and Plasma) use this technique to view images on our TV!
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
Explanation of Magnetic field
(for slide 15)
•
In order to have a magnetic force, we need a moving +/- charge.
•
Magnetic field lines come out of N and go into S (see diagram on slide 15)
•
Emphasize the 3 components to produce a magnetic field
#1 Moving +/- charge
#2 Changing of E-field
#3 Dipole of material (see diagram to explain)
• 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
Explanation of Magnetic field con’t
(for slide 15)
•
The unit of Tesla is a very SMALL unit
- Earth magnetic field has around 10^(-5) Tesla
- A very good Ferromagnet has around 0.5 to 1 Tesla
•
It is very hard to make material that has a very strong magnetic field, and I will explain it in more
detail later
•
Since I am doing a qualitative study on magnetism, I just gave them one of the most basic
equation for magnetic force
- Emphasize on the CROSS PRODUCT, it is not treated as a times operator. Velocity of a
+/- charge needs to be 90 degree to the magnetic field in order to have a magnetic force
Construction of Battery demo
Copper loop
Step two: tie the ears onto the battery with rubber band
Material needed
9V battery
• copper loop
• 9V battery
• rubber band
• copper ears x2
Copper ears
Rubber band
Step three: put the copper loop through
Step one: pinch the cooper ears onto the battery
the holes on the copper ears
Finish product
Video of battery demo
Show Battery Demo video under “Videos”
Battery Demo
Instruction of how to use the battery demo
#1 Set up device as above
#2 Bring the neodymium magnet close to the loop
#3 Give a kick start for the loop by flicking it
Things to tell the students
- Without the magnetic field, the loop will no move
- It is due to torque provided by the magnetic force so that the loop will go round and round
Extra interesting topic for the
battery demo
• Q: What is going on with the battery?
• Answer: The permanent magnets exert forces on the electrical currents flowing
through the loop of wire. When the loop of wire is in a vertical plane, the forces on
the top and bottom wires of the loop will be in opposite directions. These oppositely
directed forces produce a twisting force, or torque, on the loop of wire that will make
it turn. Why is it so important to sand half of one projecting wire? Suppose that the
permanent magnets are mounted with their north poles facing upward. The north
pole of the permanent magnet will repel the north pole of the loop electromagnet
and attract the south pole. But once the south pole of the loop electromagnet was
next to the north pole of the permanent magnet, it would stay there. Any push on
the loop would merely set it rocking about this equilibrium position. By sanding half
of one end of the wire, you prevent current from flowing for half of each spin. The
magnetic field of the loop electromagnet is turned off for that half-spin. As the south
pole of the loop electromagnet comes closest to the permanent magnet, the unsanded wire turns off the electric current. The inertia of the rotating coil carries it
through half of a turn, past the insulating paint. When the electric current starts to
flow again, the twisting force is in the same direction as it was before. The coil
continues to rotate in the same direction.
• 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!!)
Slide 22
•
The two diagrams show the path of a moving electron in a magnetic field
•
Use RHR #2 to verify the path of the electrons in the diagrams are correct
Right Hand Rule Question
•
Put a Ferro magnet (N or S) close the turned on CRT from the side.
•
Note that the electron beam will either go upward or downward
Q: What is the magnetic field (N or S) on the side facing the CRT?
A: It depends on which side I put my magnet close to the CRT, but I just used RHR #2 to
identified the N or S field on the Ferro magnet
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
Explanation of Magnetism
(for slide 29 and 30)
•
#1 Explain what are paired and unpaired electrons
•
#2 Recall their Chemistry 11, SPDF, electron orbital
- Using Hund’s rules and Pauli Exclusion Principle to place electrons into electron orbital
- Practice placing electrons into their orbital using the diagram on slide 30
Nitrogen
-Electrons
-Protons and Neutrons
1s2
2s2
2p3
Right
Electron
Configuration
of
Wrong
Nitrogen
Wrong
Explanation of Magnetism
(for slide 32)
•
Exercise using Hund’s rule
-use Nitrogen as an example: the first electron configuration is right and the second and
third examples of the electron configuration is wrong
There are four types of magnetism
1.Ferromagnetic
2.Paramagnetic
3.Diamagnetic
4.Ferrimagnetic
(Not going to cover)
(for slide 34)
•
Tell students that Ferrimagnetism is too hard to understand. They need some university level of
Physics in order to understand it
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
Explanation of Magnetic
Susceptibility (for slide 36)
•
Magnetic Susceptibility is to measure the magnetic property of a material
Q: What is the differences between some of the materials in the chart in slide 36?
A: They split off into three groups:
#1 negative value with small Magnetic Susceptibility
#2 positive value with small Magnetic Susceptibility
#3 positive value with relatively big Magnetic Susceptibility compare to above
#1 and #2
#4 0 Magnetic Susceptibility for Vacuum because vacuum does not contain
any material
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
Explanation of Ferromagnetic
(for slide 38)
•
Explain what is an external field
- example: current running through a solenoid
•
They do not need an external field because these material produce their own magnetic field.
Some ferromagnetic material does not produce their own magnetic field because the domain
inside of the material do not align, which I will explain in slide 42.
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
Explanation of Iron
(for slide 40)
•
Another exercise to fill in the electrons in the electron orbital of Iron.
•
Discuss that there are four unpaired electrons in the 3d orbital
#1 This is one of the reasons why Iron can produce its magnetic field
#2 The electrons seems to align spontaneously due to Quantum Mechanics effects
Why are some Ferromagnetic
doesn’t attract one another?
• Has to do with the magnetic domain of
the material
Explanation of domains of material
(for slide 42)
•
Diagram on the left shows the domains of the material do not align. This causes the magnetic
field of the material cancel each other, therefore it cannot produce its own magnetic field
•
Diagram on the right shows the domains of the material do align. Therefore, it can produce a
magnetic field on its own
Ferromagnetic material demo
•
Material needed
- neodymium magnet
- couple of paper clips
•
Instructions
#1 Show them the paper clips do not attract to any material even though they are
ferromagnetic (domains are not align).
#2 Attract one of the paper clip to the neodymium magnet
#3 use the paper clip that is on the neodymium magnet to attract another paper clip
Q: How come it attracts now?
A: The neodymium magnet help align the domain in the paper clip
#4 Gently remove the neodymium magnet and show that the paper clip can still attract to
each other
Q: Why?
A: It stays align until you pull them away
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
Paramagnetic material demo
(for slide 45)
•
Try to attract an aluminum can with a neodymium magnet. It cannot
Q: Why?
A: It is because of the Magnetic Susceptibility of paramagnetic materials are too weak
compared to Ferromagnetic
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)
Instructions of how to use the levitation device
#1 Set up the device
#2 Place orange stud with the magnet side facing away from the solenoid
#3 Place the stud so you can feel the solenoid is attracting the stud
#4 Gently remove your hand so the device and do its work
Explanation of how it works
- solenoid provide the magnetic field, so the magnet will attract upward
(para and ferromagnetic property).
- detector in the bottom is to sense if the stud is moving up or down. If it moves
too high, the detector will cut the current so the stud will come back down by
gravity. If it moves too low, the detector will send current in the solenoid to
generate a magnetic field, so the stud will go up again by the attraction between the magnet
and magnetic field
Video of ferromagnetic levitation
Show Ferromagnetic levitation video under “Videos”
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
• Instructions of how to use the magnets
#1 Set up the magnets
#2 Gently place the pyrolytic carbon in the middle of the four magnets
Applications of Magnetism
MRI (magnetic resonance images)
Superconductors
Application of Magnetism
(for slide 53)
•
•Magnetic Resonance Images (MRI)
- These machines can produced up to 7 Tesla to make very good images of the body
Q:
A:
How to produce a strong magnetic field ?
Build a giant solenoid
Q:
A:
What is the problem with producing a strong magnetic field
#1 Material cannot stand the magnetic force with the magnetic field; resulting in
collapsing the material
#2 High velocity of current running through the solenoid produce a lot of heat.
This can result in melting the solenoid if the magnetic field is too strong
•
•Super conductors
- superconductors are very useful because it does not have any resistant with other
material
- all superconductors are diamagnetic
•
•Animals
- Animals such as sharks and turtles use the Earth magnetic field to detect their position
and direction (Research has not been finished, a few published paper support this theory)
Applications of Magnetism
• Maglev Trains
Maglev train demo
• Instruction of how to use the Maglev train
#1 Set up the train track
#2 Place the train onto the track
#3 Push the train
Discuss the problems that the demo had
- too much friction from the side of the train because this is a ferromagnetic levitated train
(solution is discussed in the next slide). Therefore, the train will move side to side causing friction
with the track
- human generated power
Application of Magnetism con’t
(for slide 55)
•
WHY?
Q: why do people invent Maglev trains?
A: Less friction than trains with wheels because it does not need wheels to run
•
HOW?
- first it levitates using superconductors
Q: Why do we need superconductors to levitate, why can’t we use ferromagnetic material
like the train in the demo?
A: The problem with using ferromagnetic material to levitate the train is because
ferromagnetic material will tend to want to align itself with the opposing field. Therefore,
the train will be unstable moving right and left (i.e. like the train in the demo). The good
thing about superconductors is because they are diamagnetic. They will always oppose a
magnetic field, so they will not move out of the track trying to align with the field like
ferromagnetic materials
Application of Magnetism con’t
(for slide 55)
•
After the train is levitated, the train can move forward by the magnetic coil from the side. These
coil can flip from N to S and vice versa to attract and repel against the magnets on the train (the
magnets on the train is fixed and cannot be flipped.