This class focuses on the study of electricity and magnetism. These two subjects were thought to be completely distinct (unrelated) is until around the 19th century. Electricity seemed very sharp, violent and dangerous (sparks, electric shock, lightning); while magnetism seemed very soft and subtle (mysterious pushing and pulling, compass needles, navigation). While the subject of their relationship was hotly debated, the consensus was that they were not related.
Our perspective now is that they are not only related, but inseparable. It is through relativity theory and a group of differential equations associated with Maxwell and Faraday that this relationship can be most profoundly understood. In this class, since those equations are a bit beyond the scope of what we can encompass, the relationship between electricity and magnetism will be, to some degree, an article of faith*.
In the first half of the quarter we will cover electrical phenomena. This includes the study of charged particles, electric fields, the forces and interactions between charged objects, movement of charged objects (current flow), and electrical "circuits". We will begin with chapter 20 which covers electrical charges, forces and fields**; we will skip chapter 21 (Gauss's law). Then we will cover electrical potential (chapter 22), which is related to potential energy as you may have learned about it in the study of springs and gravity in physics 6a (or in other physics classes you may have taken).
Chapter 23 covers electrical energy as stored, for example, in capacitors; while chapter 24 covers electric currents and conduction via the movement of electrons in metals. This allows us to transition to electrical circuits (chapter 25), which is a bit more phenomenological than the previous four chapters. We will learn to analyze and understand current flow in circuits with resistors and capacitors using something called "Kirchhoff's Laws". This is the last chapter that treats electrical phenomena in isolation, i.e., without considering magnetism.
Our treatment of magnetism begins with chapter 26 which introduces magnetic forces and fields, as well as the relationship between magnetism and electricity. Chapter 27 deals with a phenomenon known as electromagnetic induction. This allows us to understand a third circuit-related device: the inductor. The interesting oscillatory behavior of circuits with resistors, capacitors and inductors is explored in chapter 28. This is related to the nature of light waves moving through space, through which energy is transported in the form of oscillating electric and magnetic fields. This is the subject of chapter 29. Electromagnetic waves are important and intriguing. They are less tangible than water waves or waves on a string, yet they contain energy. Unlike sounds waves which involve an oscillation in the density of air, there is no medium through which they propagate. And yet they exist. A brief discussion, with an analogy to water waves, follows here.
While the theory of ocean wave generation and propagation is complex and nontrivial, it is nevertheless possible to visualize some essential aspects of it. One can imagine wind, from storms, producing activity at the surface of the sea. That activity, following sustained winds, can evolve into waves which can travel large distances over the surface of the ocean. Waves thus generated can travel, for example, from the Southern Pacific (southeast of New Zealand) to California.
In a roughly analogous manner, movement of charged particles (particularly electrons) can generate oscillating electric fields. These oscillating electric fields, in concert with oscillating magnetic fields which are also generated by the charged particle motion, can propagate over very large distances. These are are known as electromagnetic waves. Other names include: light, radio waves, infrared radiation, ultraviolet radiation, x-rays, etc; all of which are also sometimes described in terms of photons. The study of electromagnetism culminates in the investigation and appreciation of electromagnetic waves.
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* That may be a bit of an overstatement. Even without any equations, one can observe that electrical currents create magnetic fields. (Specifically, for example, they influence compass needles.) One can also observe that changing magnetic fields (magnetic fields that change with time) can induce electric currents. These phenomenological relationships, based on observation, establish a relationship between electricity and magnetism independent from that encompassed by mathematical equations.
** The concept of a field is a subtle and important one which pervades physics.
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