Lesson A Magnetic Personality

Learning Objectives

After this lesson, students should be able to:

• List some characteristics of magnets (north and south poles, spinning electrons, etc.).
• Explain that engineers use magnets to store information.
• Give an example of magnetic memory storage (computers, flash drives, zip disks).

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Worksheets and Attachments

Pre-Req Knowledge

Some familiarity with electrons and atoms.

Introduction/Motivation

Who can tell me what a magnet is? (Listen to a number of answers from the class). Those are all great answers! Well, today we are going to talk about what makes a magnet, and how engineers use magnets to store information.

Can anyone think of something that we use to store information? (Possible answers: Computer, flash drive, hard drive, floppy disk.) You're right! And guess what! Not everyone realizes this, but most of the electronic devices that you just named use magnets to store information! That's pretty neat, isn't it? Who knows why it is important for us to be able to record and store information? (Possible answers: So we can keep track of important information and access it later). Right! Here's another question for you — who designs, tests and builds devices that use magnets (such as computers or flash drives)? Here's a hint — it starts with an "E"! That's right — engineers do! Engineers need to understand how magnets work so that they can make neat devices that help people and make our lives easier or better in many ways.

What makes a magnet? Did you know that magnets are actually created by tiny spinning electrons in an atom? The electrons in an atom are in constant motion. The electrons move about the nucleus and spin like a top, creating a tiny magnetic field (space around the magnet where magnetic forces can be noticed). If electrons are spinning in the same direction there is more magnetism, while electrons spinning in opposite directions cancel out each others' magnetic fields. Magnetic fields are invisible; we can only see the effects of the magnetic force.

Also, all magnets have a north pole (N) and a south pole (S). These names are used because if a bar magnet is suspended freely in the air, one end always points northward in the earth's magnetic field, while the other points southward. Unlike poles attract each other and stick together (S and N) while like poles push each other away (N and N, or S and S).

There are also special magnets called electromagnets. These magnets are created by wrapping a coil of wire around a magnetic material, usually iron or steel, and running electricity through it. The electric current turns the magnetic material in the middle of the coil into a magnet.

This idea of using magnets to store information is called magnetic memory storage. It is actually a pretty simple idea. Here's how it works: Inside a computer hard drive are disks called platters. The platters are coated with a material similar to rust. When this material is exposed to a magnet, it becomes magnetized. Many little electromagnets are used to arrange, or "write" the magnetism into specific patterns, and recognize, or "read" it. These little electromagnets are called "read/write heads." They are located on an arm that moves above the disk, or platter. The position of all the little electromagnet heads in the arm over the top of the platter allows them to read and write information to the disk. Some devices that use magnetic memory storage are computers, flash drives, and zip or floppy disks. Credit, debit and ATM cards also have magnetic information storage on the dark strip on one side. The magnetic strips contain bank and account information.

Magnets come in many different shapes and sizes. Many of the magnets used in machines are actually electromagnets rather than permanent magnets. The magnetic field of an electromagnet can be turned on and off as you turn the electricity to the coiled wire on and off. However, even though we call them "permanent," permanent magnets are not really permanent either. They can be de-magnetized by hitting them with a hammer or heating them up. Why do you think that engineers would rather use a magnet you can turn on and off instead of a permanent magnet? (Answer: You can demagnetize a permanent magnet by hitting or heating it, which makes it useless.)

If you place a permanent magnet near something that provides magnetic storage, such as a hard drive, it erases the memory or stored information! By contrast, an electromagnet can only erase memory when it is turned on. Do you know some other objects that you need to be careful not to expose to magnets? (Possible answers: Credit cards, cassette tapes, computer disks, and televisions.) This is because a magnet can erase the memory of those items as well. Today, we are learning about one use of magnets — magnetic storage. Engineers use magnets in all sorts of devices including motors, appliances and magnetic storage! Following the lesson, refer to the associated activity Magnetic Attraction for students to conduct conduct several investigations with magnets to learn about magnetic properties. 

Lesson Background and Concepts for Teachers

Some materials are magnetic all the time. Other materials can be magnetized by rubbing them in one direction with a magnet or by placing them near an existing strong magnet. A material that can be magnetized easily tends to also demagnetize easily, while a material that is difficult to magnetize tends to not demagnetize as easily. Heating, dropping or hammering a magnet decreases its strength and may demagnetize it.

All magnets have a north pole (N) and a south pole (S). These names are used because one end of a suspended magnet always points northward in the earth's magnetic field while the other points southward. Unlike poles attract while like poles repel. This also means that the north geographic pole is a south (S) magnetic pole and the south geographic pole is a north (N) magnetic pole.

If you push the N poles of two magnets toward each other you work against a repulsive magnetic force. Likewise, if you pull apart two magnets that have their N and S poles together, you work against an attractive magnetic force.

What Causes Magnetism?

Magnetism is produced by moving electric charges. The electrons in a material are in constant motion. The electrons move about the nucleus and spin like a top, creating a magnetic field. The spinning of the electrons creates most of the magnetism in most atoms. If electrons are spinning in the same direction there is more magnetism, while electrons spinning in opposite directions cancel out each others' magnetic fields. In most atoms, the electrons are spinning in opposite directions and the magnetic fields cancel. However in the atoms of some materials, such as iron, cobalt and nickel, not all of the magnetic fields cancel and each atom is actually a tiny magnet.

In a material, clusters of atoms line up with each others' magnetic fields — just like a compass lines up with the Earth's magnetic field — to produce magnetic domains. Each magnetic domain is also its own tiny magnet and therefore has an N and an S pole. In a piece of de-magnetized iron, the domains are randomly oriented. In a piece of strongly magnetized iron, the domains are all aligned.

Many electronic devices produce magnetic fields and can be disturbed by other magnetic fields. Electrical and computer engineers design computers and communications equipment to be shielded from unwanted magnetic fields that might come from outside the equipment.

What is the Source of Earth's Magnetic Field?

The Earth's magnetic field is shaped as if a strong bar magnet were placed near the center of the Earth with its S pole near the north geographic pole and its N pole near the south geographic pole (see Figure 1). The Earth's magnetic field is inclined at about 11 degrees from its axis of rotation, and, of course, is three-dimensional. Use of a common compass only indicates the magnetic field in a plane tangent to the surface of the Earth. There is also a component of the magnetic field perpendicular to the surface of the Earth.

The Earth's magnetism is also caused by moving electric charges. Even though the core (both the solid inner core and liquid outer core) consists of iron and nickel, it is too hot for the core to be a magnetized chunk of metal. Moving charges — electrons and ions — in the molten material of the liquid outer core produce the magnetic field. Scientists think that there are two reasons for the movement of the charges: 1) The Earth's rotation on its axis, and 2) convection currents from heat rising off the solid inner core. The Earth's magnetic field has reversed direction many times throughout geologic time. Aerospace engineers design satellites to withstand the effects of the Earth's magnetic field and the charged particles that flow along it. The field can affect a satellite's orientation and the charged particles can disrupt sensitive electronics.

Magnetic Storage

Inside a hard drive is a highly polished aluminum or glass disk, called a platter. This disk is coated with an iron oxide (Fe₂O₃) very similar to rust. When the iron oxide is exposed to a magnet, it is magnetized. The disk spins at very high rates (3,600-7,200 rpm). Tiny electromagnets "write" and "read" the magnetism. These read/write heads are positioned over the platter on an arm that moves the heads between the edge and the hub of the disk.

Information is coded in the magnetization of tiny areas on the disk, known as magnetic domains. Magnetization of a domain represents the number 1 while the number 0 is represented by a lack of magnetization. Therefore the information on a hard disk is stored as strings of zeroes and ones. This type of data is called binary because it has two possible states.

Associated Activities

• Magnetic Attraction - Students conduct several investigations with magnets to learn about magnetic properties.

  Watch this activity on YouTube

Lesson Closure

What can you tell me about a magnet? (Possible answers: It has north and south poles, it is caused by spinning electrons, it can stick things together or push them apart, it can store information or erase information, etc.) What is an electromagnet? (Answer: It is a magnet that is made when electricity is pushed through a coil of wire around a magnetic material.) How are electromagnets and permanent magnets different? (Answer: You can turn an electromagnet on and off.) Do you remember how you can demagnetize a magnet? (Answer: By heating or dropping/hammering it hard.) What is one way we talked about today that engineers use magnets? (Answer: For magnetic memory or information storage.) Can you think of any examples of magnetic memory storage? (Answers: Computer hard drives, zip disks, flash drives.)

Vocabulary/Definitions

Binary: A number representation consisting of zeros and ones (only two possible states).

Electromagnet: A fabricated magnet made of a coiled wire wound around an iron core (or any magnetic material such as iron, steel, nickel, cobalt) with electric current flowing through it to produce magnetism. The electric current magnetizes the material.

Electromagnetism: Magnetism created by an electric current.

Electrons: Very small, negatively-charged particles of an atom.

Engineer: A person who applies her/his understanding of science and mathematics to create things for the benefit of humanity and our planet. This includes the design, manufacture and operation of efficient and economical structures, machines, products, processes and systems.

Magnet: Something that attracts iron and generates a magnetic field.

Magnetic domain: A cluster of atoms in which the magnetic fields of all the atoms are aligned.

Magnetic field: The portion of space around a magnet where the magnetic forces of the object can be detected.

Magnetic memory storage: Using magnets to store information. For example, computer hard drives, flash drives, floppy drives, zip drives.

Permanent magnet: A piece of magnetic material that retains its magnetism after it is removed from a magnetic field.

Assessment

Pre-Lesson Assessment

Pre/Post Quiz: Before beginning the lesson, have students complete the attached 10-question Electricity and Magnetism Quiz to gauge their baseline understanding of the subject matter. Then give the same students the same quiz after completion of this lesson (and its associated activities), to gauge their knowledge gain.

Discussion Questions: Take note of student responses to the following questions.

• Have you ever wondered how magnets work?
• What is a magnet?
• What do magnets do?
• What happens if you put two magnets together? (Use two magnets to demonstrate.)
• How could a magnet be useful?

Post-Introduction Assessment

Voting: Ask a true/false question and have students vote by holding thumbs up for true and thumbs down for false. Tally the votes and write the number on the board. Give the right answer.

• True or False: Magnets have two poles — an N, or north, pole and an S, or south, pole. (Answer: True)
• True or False: If we put two same or like magnet poles next to each other (S and S) they would stick together. (Answer: False. Opposite magnetic poles attract and like poles repel each other.)
• True or False: Engineers design ways to store information in computers. (Answer: True)
• True or False: Magnets can erase data stored on a hard drive or a credit card. (Answer: True)
• True or False: Heating a magnet does not affect it at all. (Answer: False. Heating a magnet can demagnetize it.)

Lesson Summary Assessment

Roundtable: Divide the class into teams of 3-5 students each. Ask the class the questions below, instructing the teams to list as many items as possible. Begin by having one student on each team start a list by writing down one answer, and passing the paper on to the next person. Conclude by having the teams share their lists with the class.

• What is an object or device that has a magnet in it? (Possible answers: Tape recorder, VCR, refrigerators, appliances, anything with a motor.)
• What is a material or object that can be magnetized? (Possible answers: Iron nail, steel nail, tacks, paper clips, sewing needle, screwdriver, any piece of metal with iron in it).

Pre/Post Quiz: After completion of this lesson (and its associated activities), have students complete the attached 10-question Electricity and Magnetism Quiz to evaluate their knowledge gain.

Lesson Extension Activities

Have the students build a magnetometer to monitor the Earth's magnetic field. See the soda bottle magnetometer at http://image.gsfc.nasa.gov/poetry/workbook/magnet.html or another version at http://www.windows.ucar.edu/tour/link=/teacher_resources/magnetometer_edu.html.

For a math extension, have students learn how to write numbers in the binary number system. A good resource is the Binary Math page at http://computer.howstuffworks.com/bytes7.htm.

Have students make drawings to explain the orientation of Earth's magnetic field and the direction a compass would point when located at various places on Earth.

Additional Multimedia Support

To help students understand the invisible magnetic fields, show them the pattern made by a bar magnet and iron filings with excellent photographs at Wikipedia (http://en.wikipedia.org/wiki/Magnetism) or NASA (http://science.msfc.nasa.gov/ssl/pad/solar/magmore.htm).

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.