What Kind of Materials are Magnetic?

Personal Lab 9

Background

Long ago people noticed that certain rocks called lodestones seemed to have the innate and unusual property of attracting other special rocks. These dark colored rocks also had the interesting property that, when suspended from a string, they always point toward the north. For many years sailors used lodestones for navigating their ships across the oceans. We now know that lodestones are a special kind of rock called "magnetite".

As techniques for separating different materials from the rocks became more sophisticated, it was found that some materials had magnetic properties and some did not.

Early explorers navigated the oceans guided by lode stones which were used to indicate the directions of the Earth's north and south magnetic poles. We use compasses for the same purpose today. In fact, we know now that the Earth is a giant magnet (although we do not yet fully understand what causes its magnetism). Magnets have a great variety of uses in our daily lives from fastening notes to refrigerator doors to turning shafts of the motors found in most household appliances. We make use of magnetic effects everytime we store or retrieve information to the disk drives of our computers. Also our credit cards identify us through a magnetic code embedded in a strip on the card.

What causes this interaction we call magnetism? How is magnetism different from the electrical and gravitational interactions?

Purpose

1) To investigate how a magnetic compass works.

2) To characterize materials as "magnetic" or "non-magnetic".

Procedure

1. Carry your magnetic compass with you for a day. At various times examine it to see what the needle indicates. Hold the compass near and far from various objects, both inside and outside buildings and your home. Record your observations.

2. Design and perform an experiment to test various objects and materials around your home for magnetic effects.

3. Tie a string around the middle of your bar magnet, so that it balances in the middle. Suspend the magnet from the ceiling somewhere where it will not be disturbed, and observe the hanging magnet’s behavior over several days. Record your observations.

Questions

1) How did your magnetic compass orient itself in various locations? Does the needle always point North? Explain.

2) What is the needle of your compass? Explain your reasoning.

3) What do you think causes your compass to orient itself? State your hypothesis to explain this phenomenon. How can you test your hypothesis?

4) Describe how you tested materials to be magnetic or non-magnetic.

5) List the materials you found to be magnetic and those which were non-magnetic.

6) Are any materials you tested both magnetic and electrical conductors?

7) What distinguishes a magnet from "magnetic material"?

8) What distinguishes a magnet from "non-magnetic material"?

9) What distinguishes "magnetic" from "non-magnetic" materials?

10) Describe what happened to the bar magnet suspended from the string. State a hypothesis that might explain your observations.

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Last modified 9 Aug 1997
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