Exploratories

Properties of Magnets

Purpose:

To describe the basic properties of magnets.

Materials:

Two small magnets; magnetic and non-magnetic box of paper clips; drill bit; nails;
aluminum; copper, zinc, gold or silver ring; U.S. coins. Canadian coins, and magnetic toys, if available.

Procedure:

1. Show that magnets attract and repel other magnets when held near them.
Balance one magnet on the edge of a watch glass to reduce friction.

2. Demonstrate that a magnet will pick up a cardboard box if it is filled with paper
clips, but will not attract such common metals as aluminum, copper, or zinc.

3. Attach a nail to a permanent magnet and then use the combination to pick up paper clips. With the paper clips still hanging from the nail, detach the nail from the
magnet. Note what happens to the paper clips. Soft iron such as nails can be made
into a temporary magnet, whereas steel can be made into a permanent magnet.

4. Stroke a piece of tool steel such as a drill bit with a permanent magnet. The
stroking should be done lengthwise from top to bottom. Move the magnet away
when returning it to the top of the drill bit. Use the drill bit to pick up paper clips.

Summing Up:

Magnetic forces exist between magnetic materials. Unlike magnetic poles attract, while like poles repel. The strength of attraction or repulsion between two magnets is a function of distance between them.

Magnets and Their Interactions

Problem:

How do magnets interact? What is a magnetic field?

Materials:

Refrigerator magnets, fifteen small compasses, 30 lg paper clips, 15-30 cm
lengths of string, post-it notes (small)

Procedure:

1A: Give each student a few refrigerator magnets. Have them describe the magnets. Then have them carefully bring the magnets close together and describe what happens.
Turn both magnets over and try again. Turn only one magnet over and describe
what happens.

1B: Give each pair of students a compass and have them tell what happens to the
compass. Try the other side of the magnet, what happens? Determine the location of the poles of the magnets.

1C: Put magnets and compasses aside and give them two paper clips, touch and
describe what happens.

1D: Use a magnet and pick up the paper clips, now touch the paper clips together.
What happens?

1E: Open up a paper clip and tie string to the middle of the clip. Hold the string
and notice what happens to the clip. Describe.

1F: Have students use post-it notes to label magnets with north and south poles.

CONCEPT DEVELOPMENT:

A compass is a device that allows a magnetic needle to freely point toward the Earth's north magnetic pole. The north magnetic pole of the Earth will attract the north-seeking pole of a magnet, and that pole is labeled 'N'.

A magnetic field is produced by the net angular momentum of an atom. Once the field is produced, we then concern ourselves with the effect of bringing "our" magnet or "our" moving charge 'qv', or "our" current-carrying wire into that field.

The strength of a magnetic field (B) is determined by the amount of moving electric charge. 'B' is analogous to 'g' and 'E', and thereby defines the magnetic equivalent to Newton's law of acceleration in a gravitational field. (B=F/qv) .'B' is measured in Teslas (T).

A moving charge will generate a magnetic field that circulates around the moving charge and its plane of motion is perpendicular to the direction in which the charge is moving.

A moving electric charge, or a current-carrying wire, in a magnetic field will experience a deflecting force (F=qvxB).

Fill in each blank with the appropriate word.

1. Attraction or repulsion of charges depends on their signs, positives or negatives.
Attraction or repulsion of magnets depends on their magnetic _____: or ________.

2. Opposite poles attract; like poles ______.

3. A magnetic field is produced by the _________ of electric charge.

4. Clusters of magnetically aligned atoms are magnetic _______.

5. A magnetic ________ surrounds a current-carrying wire.

6. When a current-carrying wire is made to form a coil around a piece of iron, the result is an ________.

7. A charged particle moving in a magnetic field experiences a deflecting ______ that is maximum when the charge moves _________ to the field.

8. A current-carrying wire experiences a deflecting _______ that is maximum when the wire and magnetic field are ________ to one another.

9. A simple instrument designed to detect electric current is the _______________;
when calibrated to measure current, it is an______________; when calibrated to measure voltage, it is a _______________.

10. The largest size magnet in the world is the ___________ itself.