Under the Hood … Building a Magnet Model

Author(s): Seth Bush
Subject: Physics
Grade Level(s): Grade 4
Topic: Magnetism
Big Idea(s):

Students know how to build a simple compass and use it to detect magnetic effects, including Earth’s magnetic field.

Students know electric currents produce magnetic fields and know how to build a simple electromagnet.

Students know that magnets have two poles (north and south) and that like poles repel each other while unlike poles attract each other.

Students know magnetic materials and electric currents (moving electric charges) are sources of magnetic fields and are subject to forces arising from the magnetic fields of other sources.

What you need:

Nails
Nippers
Compass or set of compasses
Magnet Kit

Grouping: Work in Groups of 2
Vocabulary Words:
Time Needed:

Summary:

In this activity we will break apart magnets to develop a model for how a permanent magnet works.

This activity is modeled after “Physics for Everyday Thinking, Model of Magnetism”

Learning Goals / Objectives:

Students will learn how a domain model can be used to describe how magnets work.

Background

This activity is very simple and should not take too long. You may want to include elements of “Electromagnet Challenge” or “Compass Tweak” to include making permanent magnet using an electromagnet.

Safety
This activity has little to no risk associated with it. Common sense care should be taken when handling the sewing needles.

Anticipatory Set:

Driving Questions
1. How does a magnet work?
2. What model best describes how a magnet works?

Instructions / Activities:

In this activity we are going to do the unthinkable. .. We are going to break a magnet. Don’t panic! It is all in the name of science. We are going to search for the illusive magnetic monopole. That is, either a South pole all by itself or a North pole all by itself.

Non-Destructive Mode
Make sure you have the following:

A stack of magnets (disks or rectangles will work best).

a compass

1.) Label the North and South poles of the stack of magnets (all together) .
2.) Make a prediction:

What do you think will happen when you break the magnet stack in half?

Will one piece be North and the second piece South?

Will both the pieces have a North and South pole?

3.) Break the stack in half. Label the poles of each half. Record your observations. Were your predictions close?
4 .) What do you suppose will happen if you break one of the half-stacks in half? Try it. Do you have a smug sense of cleverness? If not, try it again.

Follow up Questions:
1.) Do your observations support the idea that magnetic monopoles exist?
2.) Do your observations prove that magnetic monopoles do not exist?

Destructive Mode
1.) Imagine the magnetized nail (a. from “Magnet Maker”) you made by rubbing a nail with a permanent magnet. Sketch what you think might be different about the nail that has not been rubbed and a nail that has been rubbed.

Share your model with your neighbor. Refine your model if you want.

2.) Based on your refined model. .. lets make a prediction. What would happen if the nail is cut in half? Make a predictive sketch below, use N to indicate a north pole, S to indicate a south pole and X in indicate no pole at all.

3.) Pause. Share your prediction with the group.

4.) Test your prediction. .

Remake nail a. (use your compass to make sure it behaves the way you expect)

Cut nail a. in half. Test the ends of each half with a compass. Use your observations to complete the sketch below. Again, use N to indicate a north pole, S to indicate a south pole and X in indicate no pole at all.

5. Based on your observation in 4 .) Refine your model.

6. Make a prediction and test your model … Again .

Based on your refined model. .. What would happen if the nail is cut in two unequal pieces (say 113 and 2/3)? Make a predictive sketch below. Again , use N to indicate a north pole, S to indicate a south pole and X to indicate no pole at all.

Remake nail a. (use your compass to make sure it behaves the way you expext)

Cut nail a. in two unequal portions. Test the ends of each half with a compass. Use your observations to complete the sketch below. Again, use N to indicate a north pole, S to indicate a south pole and X in indicate no pole at all.

7.) Does your model predict the existence of magnetic monopoles?

8.) Last test. Obtain a sealed test tube filled with iron filings. DO NOT OPEN THE TUBE!!!

Shake the tube a few times.

Use a compass to determine if the tube have a north and a south pole.

Just like with the nail, rub the tube from cap to tip along the north pole of a strong magnet. Again, only rub in one direction. Use a compass to determine if the tube have a north and a south pole.

10.) Make a prediction: Based on your model, what will happen to the poles if you shake the tube? Test your prediction.

Can you explain your observations in 10. using your model for magnetism?

Assessment:

Teacher’s Discretion

Wrap-up / Closure: