# Magnetism

## Connection for AP® Courses

Magnetism plays a major role in your everyday life. All electric motors, with uses as diverse as powering refrigerators, starting cars, and moving elevators, contain magnets. Magnetic resonance imaging (MRI) has become an important diagnostic tool in the field of medicine, and the use of magnetism to explore brain activity is a subject of contemporary research and development. Other applications of magnetism include computer memory, levitation of high-speed trains, the aurora borealis, and, of course, the first important historical use of magnetism: navigation. You will find all of these applications of magnetism linked by a small number of underlying principles.
In this chapter, you will learn that both the internal properties of an object and the movement of charged particles can generate a magnetic field, and you will learn why all magnetic fields have a north and south pole. You will also learn how magnetic fields exert forces on objects, resulting in the magnetic alignment that makes a compass work. You will learn how we use this principle to weigh the smallest of subatomic particles with precision and contain superheated plasma to facilitate nuclear fusion.
Big Idea 1 Objects and systems have properties such as mass and charge. Systems may have internal structure.
Enduring Understanding 1.E Materials have many macroscopic properties that result from the arrangement and interactions of the atoms and molecules that make up the material.
Essential Knowledge 1.E.5 Matter has a property called magnetic permeability.
Essential Knowledge 1.E.6 Matter has a property called magnetic dipole moment.
Big Idea 2 Fields existing in space can be used to explain interactions.
Enduring Understanding 2.D A magnetic field is caused by a magnet or a moving electrically charged object. Magnetic fields observed in nature always seem to be produced either by moving charged objects or by magnetic dipoles or combinations of dipoles and never by single poles. 
Essential Knowledge 2.D.1 The magnetic field exerts a force on a moving electrically charged object. That magnetic force is perpendicular to the direction of the velocity of the object and to the magnetic field and is proportional to the magnitude of the charge, the magnitude of the velocity, and the magnitude of the magnetic field. It also depends on the angle between the velocity and the magnetic field vectors. Treatment is quantitative for angles of 0°, 90°, or 180° and qualitative for other angles. 
Essential Knowledge 2.D.2 The magnetic field vectors around a straight wire that carries electric current are tangent to concentric circles centered on that wire. The field has no component toward the current-carrying wire. 
Essential Knowledge 2.D.3 A magnetic dipole placed in a magnetic field, such as the ones created by a magnet or the Earth, will tend to align with the magnetic field vector. 
Essential Knowledge 2.D.4 Ferromagnetic materials contain magnetic domains that are themselves magnets. 
Big Idea 3 The interactions of an object with other objects can be described by forces.
Enduring Understanding 3.C At the macroscopic level, forces can be categorized as either long-range (action-at-a-distance) forces or contact forces.
Essential Knowledge 3.C.3 A magnetic force results from the interaction of a moving charged object or a magnet with other moving charged objects or another magnet.
Big Idea 4 Interactions between systems can result in changes in those systems.
Enduring Understanding 4.E The electric and magnetic properties of a system can change in response to the presence of, or changes in, other objects or systems.
Essential Knowledge 4.E.1 The magnetic properties of some materials can be affected by magnetic fields at the system. Students should focus on the underlying concepts and not the use of the vocabulary.