Magnetism

The basics of magnetism relies on the principal that magnetic fields are created by moving charged particles. Even "permanent" magnets are caused by "circulating" charges inside the magnet. Because the force from magnets act at a distance we will again consider the concept of fields to describe the source of the force. Magnets behave in a manner very similar to charged particles in that opposites attract, like repel and that the force is proportional to the inverse square of the distance. Magnets have a NORTH and a SOUTH instead of positive and negative. The north pole of the magnet is the one that will point to the north magnetic pole of the earth. Magnetic field lines go out of the north and into the south. One fundamental difference between static electricity and magnetism is that all known magnets are dipoles. This means that the number of field lines drawn out of the north must equal the number of lines going into the south. In terms of flux (the number of field lines passing through a surface), the flux out of the magnet is ballanced by the flux into the magnet so the total flux = 0. This fact is called Gauss's Law of Magnetism.

Because magnetism is caused by moving charged particles, magnetic fields will create forces on charged particles. To determine the direction of these we use the right hand rule. The right hand rule that I will describe is different from the vector cross product rule that is done with the math equations, but it works well to predict the direction of the components. To begin, each of the three parts are at right angles to each other. The thumb of the right hand represents the direction of the velocity (thumb a ride), the index finger represents the direction of the magnetic field (point north) and the other three fingers represent the direction of the force (with considerable strain they can form the letter F). We use the right hand for positive charges and the left hand for negative charges.

If moving charged particles create a magnetic field. The question "can a magnetic field move charged particles?" The answer is yes - ONLY IF the magnetic field is changing. This changing magnetic field induces a voltage in a circuit. The rules for the directions are the same as above where the force becomes the electromotive force (EMF) or voltage, the same direction as the current that is produced.

The ability to "induce" a current brings in the concepts of Lens' Law, a special consequence of the law of conservation of energy, and the use of transformers in AC circuits. Students should know how transformers work and the advantages of being able to change the voltage in long distance power transmition lines.

 Physics Quizzes & Homework Word PDF Magnetism Homework Magnetism Quiz 1 Magnetism Quiz 1 Magnetism Quiz 2 Magnetism Quiz 2 Magnetism Quiz 3 Magnetism Quiz 3 Magnetism Quiz 4 Magnetism Quiz 4 Electromagnetic Rules Electromagnetic Rules