Ch0202 - Chapter 2 The Electric Field: Description and...

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Chapter 2 The Electric Field: Description and Effect 9 2 The Electric Field: Description and Effect An electric field is an invisible entity 1 which exists in the region around a charged particle. It is caused to exist by the charged particle. The effect of an electric field is to exert a force on any charged particle (other than the charged particle causing the electric field to exist) that finds itself at a point in space at which the electric field exists. The electric field at an empty point in space is the force-per-charge-of-would-be-victim at that empty point in space. The charged particle that is causing the electric field to exist is called a source charge. The electric field exists in the region around the source charge whether or not there is a victim charged particle for the electric field to exert a force upon. At every point in space where the electric field exists, it has both magnitude and direction. Hence, the electric field is a vector at each point in space at which it exists. We call the force-per-charge-of-would-be-victim vector at a particular point in space the “electric field” at that point. We also call the infinite set of all such vectors, in the region around the source charge, the electric field of the source charge. We use the symbol E h to represent the electric field. I am using the word “victim” for any particle upon which an electric field is exerting a force. The electric field will only exert a force on a particle if that particle has charge. So all “victims” of an electric field have charge. If there does happen to be a charged particle in an electric field, then that charged particle (the victim) will experience a force E F h h q = (2-1) where q is the charge of the victim and E h is the electric field vector at the location of the victim. We can think of the electric field as a characteristic of space. The force experienced by the victim charged particle is the product of a characteristic of the victim (its charge) and a characteristic of the point in space (the electric field) at which the victim happens to be. The electric field is not matter. It is not “stuff.” It is not charge. It has no charge. It neither attracts nor repels charged particles. It cannot do that because its “victims”, the charged particles upon which the electric field exerts force, are within it. To say that the electric field attracts or repels a charged particle would be analogous to saying that the water in the ocean attracts or repels a submarine that is submerged in the ocean. Yes, the ocean water exerts an upward buoyant force on the submarine. But, it neither attracts nor repels the submarine. In like manner, the electric field never attracts nor repels any charged particles. It is nonsense to say that it does. If you have two source charge particles, e.g. one at point A and another at point B, each creating
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This note was uploaded on 02/29/2012 for the course PHYS 227 taught by Professor Rabe during the Fall '08 term at Rutgers.

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Ch0202 - Chapter 2 The Electric Field: Description and...

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