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