Magnetism

Learning Objectives

• Understand the Basics of Magnetism: Students will be able to explain what magnetism is, identify magnetic materials, and describe the properties of magnets, including poles and magnetic fields.
• Explore Magnetic Forces and Fields: Students will investigate how magnetic forces work, including attraction and repulsion between magnets, and visualize magnetic field lines using iron filings or similar materials.
• Applications of Magnetism: Students will learn about the practical applications of magnetism in everyday life, such as in compasses, electric motors, and magnetic storage devices.
• Electromagnetism: Students will understand the relationship between electricity and magnetism, including how electromagnets work and their uses in various technologies.

Magnetism is a physical phenomenon produced by the motion of electric charge, resulting in attractive and repulsive forces between objects. Students will learn that magnetism is a fundamental force of nature, similar to gravity and electricity.

Magnetic materials are substances that can be influenced by magnetic fields. Common examples include iron, nickel, and cobalt. These materials can become magnets themselves when exposed to a magnetic field.

Properties of magnets include:

• Poles: Every magnet has two poles, called the north pole and the south pole. These poles are the points where the magnetic force is strongest. Opposite poles attract each other, while like poles repel each other.
• Magnetic fields: Magnets create invisible areas of influence called magnetic fields. These fields can be visualized using iron filings, which align along the field lines. The magnetic field is strongest near the poles and weaker further away.

Figure 1. The north pole of a compass needle points toward the south pole of a magnet, which is how today’s magnetic field is oriented from inside Earth. It also points toward Earth’s geographic North Pole because the geographic North Pole is near the magnetic south pole. Source: University Physics Volume 2

Geographic North Pole is not a Magnetic North Pole

Magnetism has intrigued humans since ancient times. The ancient Greeks were among the first to discover magnetic materials, such as lodestones, which naturally attract iron. Despite its long history, magnetism remained somewhat enigmatic because its effects are not as visually apparent as those of electricity. For instance, while you can see the dramatic flash of a lightning bolt, the force that causes a compass needle to point north is invisible.

Over centuries, people gradually uncovered the properties of magnets. They observed that certain materials could attract or repel each other and that magnets always had two poles: north and south. These observations laid the groundwork for understanding magnetic fields, which are the areas around a magnet where magnetic forces are exerted.

The connection between magnetism and electricity was a significant breakthrough in the nineteenth century. Physicists like Hans Christian Ørsted and Michael Faraday discovered that electric currents could generate magnetic fields and that changing magnetic fields could induce electric currents. This relationship, known as electromagnetism, revolutionized science and technology, leading to the development of electric motors, generators, and many other devices.

Figure 2: Portraits of two pioneering scientists: Michael Faraday (left), known for his groundbreaking work on electromagnetic induction, and Hans Christian Ørsted (right), who discovered the relationship between electricity and magnetism. 

In this section, we will learn the fundamental concepts of magnetism. We'll explore how magnetic fields are created and how they interact with materials. By understanding these basic ideas, we can appreciate how magnetism fits into the broader picture of physical forces and its crucial role in modern technology.

Test your understanding

Question: Suppose you cut off the white part of a compass needle and discard it. Then, you drill a hole in the remaining red part of the needle. Will the red part still swing east and west?

Answer:

If you cut off the white part of the compass needle and discard it, the remaining red part will still retain its magnetic properties. However, drilling a hole in the red part could affect its balance and ability to pivot freely. A compass needle works because it is magnetized and can rotate freely to align with Earth's magnetic field. If the needle is unbalanced or damaged, it might not swing properly. The red part, which is typically the north-seeking pole, should still point towards magnetic north, but its movement might be hindered if the needle is not able to pivot smoothly. Therefore, while the red part will still have magnetic properties, its ability to swing east and west might be compromised due to the physical alterations.

Hans Christian Ørsted's experiment demonstrated the relationship between electricity and magnetism in a simple yet profound way. In his experiment, Ørsted placed a compass near a horizontal wire carrying an electric current. When the compass was positioned directly above the wire, the electric current created a magnetic field that influenced the compass needle to swing in a specific direction. However, when the compass was moved directly below the wire, the direction of the magnetic field reversed, causing the compass needle to swing in the opposite direction. This happens because the magnetic field around a current-carrying wire forms circular loops, and the direction of these loops depends on the direction of the current. When the compass is above the wire, the magnetic field loops in one direction, pushing the compass needle one way. Conversely, when the compass is below the wire, the magnetic field loops in the opposite direction, pushing the needle the other way. Ørsted's experiment was crucial in showing that electric currents can create magnetic fields and that these fields can change direction based on the position of the compass relative to the wire. This discovery laid the foundation for the field of electromagnetism, which has numerous applications in modern technology.