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Magnetism
Physical Science
Magnetism is a Property of Moving Electrons
Magnetism is the ability of some substances to attract iron, steel, and some other metalsMagnetism is a property of an electric charge in motionEvery moving electron has a magnetic field around itEach electron in every atom is a tiny magnet
Magnetism is a Property of Moving Electrons
Electrons in atoms have 2 distinct motions1. They rotate upon their axis2. They orbit about the nucleus of the atomAtoms derive a magnetic effect from the orbiting motions of electrons about the nucleusAdditionally, the rotation of each individual electron on its axis provides each electron with its own magnetic field
Why are Not ALL Atoms Magnetic?
The electrons of most elements exist in pairs
The 2 members of a pair of electrons spin in opposite directions
The orientation of their magnetic fields is such that they oppose each other
The 2 magnets pull in opposite directions and cancel their forces out
Why are Not ALL Atoms Magnetic?
The magnetic fields of the individual electrons orbiting about the nuclei of atoms are oriented in all directions, with no particular patternThe net effect is that no external magnetic field is detectableThe cancellation effects associated with the pairing of atoms according to their spin and the randomness of their orbiting motion account for the fact that most substances in nature possess little or no external magnetic field
Some Materials are Magnetic
To possess a magnetic field, a substance must meet 2 requirements:
1. Some of its atoms must possess unpaired electrons, giving each atom strong magnetic properties
2. The magnetic fields of some atoms must be aligned so that the magnetic effects are not cancelled out
The theory of magnetic domains accounts for both of these factors
Theory of Magnetic Domains
The atoms of 3 elements possess electrons with unpaired spinsThese elements are: iron, nickel, and cobaltA bar of these metallic elements is composed of small microscopic regions called domainsWithin these domains, all the magnetic fields of individual atoms are alignedThis in effect makes each domain a tiny, strong magnetTo make an entire sample of a substance magnetic, you need to align the domains so that their magnetic effects add together
Magnetic DomainsIn most materials the magnetic fields of the atoms are not organized and point in different directions
In a magnetized material most of the domains are pointing in the same direction
Magnetic Fields A magnet exerts a force beyond itself This force is called a magnetic field These two diagrams show the sphere of
influence as well as the direction of magnetic fields
MagnetismAll magnets have 2 poles: north and south
MagnetismIf 2 north poles or 2 south poles are brought near each other, they will repel
MagnetismIf a north pole and a south pole are brought near each other, they will attract
Electric Currents and Magnetic Fields
Since magnetism is a property of moving electrons as the current flows through the wire a magnetic field is generatedWhen a straight conductor is made into a coil, the magnetic effects in the center of the coil become stronger because the magnetic field is more concentrated in the center of the coilThe magnetic field is only produced when the circuit is closed
Temporary Magnets• Temporary magnets can be produced by subjecting
them to magnetic fields such as by wrapping a conducting wire around a bar of soft iron
• The magnetic field of the current-bearing wire forces some of the magnetic domains of the soft iron core into alignment, and the core becomes a magnet
• When the electric current is discontinued, the domain of the soft iron core again become randomly arranged, and the magnetic properties are lost
• Such a device is called an electromagnet
Permanent Magnets To create a permanent magnet hard iron
alloys must be used This alloy must be inserted into the center
of a STRONG current bearing conductor A strong current is needed to align the
domains of the hard iron alloy Once the domains have been aligned they
tend to remain that way
Earth has a Magnetic Field
This is due to the fluid core of the Earth
This large, iron-nickel core is a very hot, dense fluid due to the pressure of the rock layers that lie on top of it and the force of gravity
Currents of fluid, metallic matter churning slowly in the Earth’s deep interior provide electric charges
This results in the phenomenon of the magnetic field
Earth has a Magnetic Field
The Earth is like a huge but weak bar magnet
If a bar magnet is suspended at its center by a string, it will rotate until one end points toward the North Pole
This is the phenomenon behind the compass
Earth has a Magnetic Field
A compass is a tiny magnet that is free to swing about on an axis
Due to the presence of Earth’s magnetic field, the tiny compass magnet will always align itself in a north-south direction
The north-seeking pole of the compass will always point in the general direction of north
Earth’s Shifting Magnetic Field
Scientists theorize that the currents occurring in the iron-nickel core change pathways as their magnetic field affect one another
Over thousands of years, forces build up that cause a sudden “flipping” of the Earth’s magnetic field
The magnetic North Pole has resided in several locations other than its current one, including one point in the middle of the Pacific Ocean
Magnetism and Technology
Imagine getting into an elevator and being taken to the 100th floor and the elevator had no physical connection to the buildingWith the use of Maglev technology this may be a reality sooner than you thinkMaglev stands for Magnetic LevitationSuperconducting magnets are able to lift and move very heavy objectsThis technology is based on the property that like poles repel each other
Magnetism and Technology
The major focus of maglev research is in transportation specifically trainsSeveral countries are either planning or are building these trainsThese trains can travel at speeds of 150 to 500 miles per hour. There are even plans for maglev trains that will be able to travel in excess of 2,000 MPH
Magnetism and TechnologyThere are currently plans to build a maglev train between Los Angeles to Las Vegas
It will take about one and one half hours to make the 270 mile trip
That’s 180 MPH