Abstract
Physicists sometimes study matter under extreme conditions. For example, think of the emptiness of interstellar space vs. the unimaginable crush of pressure at the center of a neutron star, or an object dipped in liquid nitrogen vs. the tiles on the space shuttle during re-entry. Here's an experiment on permanent magnets in "extreme kitchen" conditions that you can try at home.Objective
The objective of this experiment is to determine whether the temperature of a magnet affects its strength.
Introduction
Magnetic fields are produced by electric currents. This could be the familiar electric current flowing in a wire, that you can measure with an ammeter. Or it could be a less familiar, microscopic current associated with electrons in atomic orbits (Nave, 2005a). Certain materials, called ferromagnetic materials, have unpaired electrons in their outermost atomic orbits that can become magnetically aligned over large distances (relative to the atomic scale). These regions of alignment are called magnetic domains.
An electric current flowing in a straight wire creates a magnetic field around the wire. The blue lines in Figure 1, below, show the orientation of such a magnetic field. Notice the "right hand" rule for determining the orientation: when the thumb of the right hand is pointing in the direction of the current, the fingers of the right hand curl in the direction of the magnetic field. You can see the effect of this magnetic field by bringing the wire close to the needle of a magnetic compass when the current is flowing. You can even make an electric current detector based on this principle (see Using a Magnet as an Electrical Current Detector.)
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| Figure 1. The illustration shows the magnetic field produced by electric current in a straight wire. When the thumb of the right hand is pointing in the direction of the current, the fingers of the right hand curl in the direction of the magnetic field (Nave, 2005f). |
A current flowing through a coil of wire (the coil is also called a solenoid) creates a stronger magnetic field than the same current flowing through a straight wire. The magnetic field is strongest at the center of the coil. Each loop in the coil contributes additional strength to the magnetic field. The more loops, the stronger the field.
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| Figure 2. The illustration shows the magnetic field produced by electric current in a coil of wire (solenoid). When the fingers of the right hand curl in the direction of the current flow, the thumb of the right hand curl points in the direction of the magnetic field (i.e. thumb points toward magnetic North pole of the solenoid). (Nave, 2005g) |
The magnetic field of a solenoid can be increased even further by placing a bar or rod of ferromagnetic material within the coil (diamagnetic and paramagnetic materials will also work, but will not retain a magnetic field when the current is turned off). The magnetic field from the coil strongly aligns all of the magnetic domains in the ferromagnetic material, creating a much stronger magnetic field than either the coil or the ferromagnetic material would have alone.
Permanent magnets are made from ferromagnetic materials. Ferromagnetic materials can "remember" their magnetic history. If a ferromagnetic material is exposed to a strong magnetic field, the magnetic domains within the material will retain at least some of the alignment induced by the external magnetic field.
When the temperature of a material is increased, what is happening on the atomic scale is an increase in the random motion of the atoms of which the material is made. You might think that random motion of atoms could affect the alignment of magnetic domains, so that increasing the temperature of a magnet would tend to decrease its strength. In fact, each ferromagnetic material has a Curie tmperature (named after Pierre Curie), above which it can no longer be magnetized. For soft iron, the Curie temperature is over 1,300°C! Your oven at home might get as hot as 260°C, so obviously 1,300°C is out of the question for a science fair experiment. But what happens to the strength of a magnet over a more approachable range of temperatures, for example from the temperature of dry ice (about −78°C) to the temperature of boiling water (+100°C)? This project shows you how to find out.
Terms, Concepts and Questions to Start Background Research
To do this project, you should do research that enables you to understand the following terms and concepts:
More advanced students may also want to study:
Questions
Bibliography
Materials and Equipment
To do this experiment you will need the following materials and equipment:
Experimental Procedure
Note: this experiment is designed for testing the temperature dependence of permanent magnets not electromagnets.
Variations
Credits
Andrew Olson, Ph.D., Science Buddies
Sources
This project is based on:
Last edit date: 2006-10-10 12:00:00
If you like this project, you might enjoy exploring careers in Physics.
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Physicist Physicists have a big goal in mind—to understand the nature of the entire universe and everything in it! To reach that goal, they observe and measure natural events seen on Earth and in the universe, and then develop theories, using mathematics, to explain why those phenomena occur. Physicists take on the challenge of explaining events that happen on the grandest scale imaginable to those that happen at the level of the smallest atomic particles. Their theories are then applied to human-scale projects to bring people new technologies, like computers, lasers, and fusion energy. |
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