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Remember the basic problem of classical electrodynamics: we have a collection of charges (the “source” charges), and we want to calculate the force they exert on some other charge (the “test” charge – Fig. 2.1). According to the principle of superposition, it is sufficient to find the force of a single source charge – the total is then the vector sum of all the individual forces.
This chapter compares the values, beliefs, and policy actions of the Clinton administration after the end of the Cold War and those of the George W. Bush administration after the events of September 11, 2001.
This chapter analyzes the effects of two important foreign policy traditions, isolationism and moral principle, as policy guides since the beginning of the Republic, and their continuing influence today.
This chapter discusses the way international law aims to help protect the environment (or does not), by focusing on relevant legal instruments and relevant instances
The chapter discusses the mechanisms international alw has at its disposal to stimulate compliance with its rules: sanctions, counter-measures, colelctive action
This chapter discusses international criminal law (fighting political crimes) and transboundary police cooperation (fighting common crimes), though mechanisms such as the ICC, but also extradition and abduction
If you ask the average person what “magnetism” is, you will probably be told about refrigerator decorations, compass needles, and the North Pole – none of which has any obvious connection with moving charges or current-carrying wires. And yet, in classical electrodynamics all magnetic phenomena are due to electric charges in motion; if you could examine a piece of magnetic material on an atomic scale you would find tiny currents: electrons orbiting around nuclei and spinning about their axes.
In this chapter we study conservation of energy, momentum, and angular momentum, in electrodynamics. But I want to begin by reviewing the conservation of charge, because it is the paradigm for all conservation laws. What precisely does conservation of charge tell us? That the total charge in the Universe is constant? Well, sure – that’s global conservation of charge. But local conservation of charge is a much stronger statement: if the charge in some region changes, then exactly that amount of charge must have passed in or out through the surface. The tiger can’t simply rematerialize outside the cage; if it got from inside to outside it must have slipped through a hole in the fence.