![]() The motions we deal with here in electro statics are "infinitesimally slow", meaning they are so slow the magnetic field is negligible and has no impact on the answer. At that point the e-field definition becomes critical to understanding what nature is doing. But, later on when Electricity and Magnetism gets more elaborate, you let charges move around relative to each other, and they start to generate magnetic fields. So what is the point of electric field? Is it just a bunch of pretend algebra?Īt this point in dealing with simple static e-fields you should be skeptical, and it should sound hokey. And then I say you get the same answer if you just use the original Coulomb's Law. Something exists in thin air that you can't see? If you are a skeptic, this sounds like a fairy tale. Then we come up with a tidy little equation that quantifies the "field". Then this thing called "electric field" is said to exist out in space near the other charge. We define the electric field starting with a version of Coulomb's Law with one of the charges set to q = 1. In the second we rely on calculus notation to do the bookkeeping for adding up all those infinitesimal dq's. The direction of E is tangential to the field line going through the field point. In peanut butter charge q_i becomes the differential charge dq, and the SUM turns into (evolves into) an INT (integral). Electric field lines end at negative charges or at infinity. So in the article you see the equation for the electric field from multiple charges The trick is to use calculus to focus down on a tiny tiny bit of the charged structure, a bit so small it can be considered a particle. In this blob of charge we have to somehow identify a charge particle. If you are presented with a problem based on peanut butter charge you have to figure how to apply particle-based Coulomb's Law. A line tangent to a field line indicates the direction of the electric field at that point. Continuous charge will include a density specification like 2 coulombs per meter, or 3 coulombs per cubic inch. When they are represented by lines of force, or field lines, electric fields are depicted as starting on positive charges and terminating on negative charges. If you see a problem statement like "assume a uniformly charged rod," that's an example of the continuous peanut butter version of charge. The charge is uniformly distributed throughout the peanut butter. You charge something by slathering it with peanut butter charge. Peanut butter isn't a collection of particles, it's something different. Coulomb's Law treats charge this way, there's a q1 and a q2.Īnother way is to think of charge as a continuous substance, like peanut butter. ![]() You can count sand particles (if there are not too many). ![]() This makes it convenient to think about charge as particles, or like a bunch of sand. We know that charge is the property of two atomic particles, electrons and protons. In the simulations we use the colors go from black (strongest field) to red, green, blue (weaker field) and then gradually fade away as the field decreases in magnitude.There are two ways to think about charge. The field vector at any point gives the direction of the field at the point, and the color of the vector shows the strength of the field. This conveys the message that every point in space has a field associated with it. If the lines are uniformly-spaced and parallel, the field is uniform.Īnother way to visualize field is to use field vectors, which are uniformly spaced. Where the field lines are close together the field is strongest where the field lines are far apart the field is weakest. An electrostatic line of force may be defined as a line whose tangent is in the direction of. ![]() The relative magnitude of the electric field is proportional to the density of the field lines. Electric fields can be mapped out by electrostatic lines of force. The direction of the field line at a point is the direction of the field at that point. Field lines start on positive charges and end on negative charges. An electric field can be visualized by drawing field lines, which indicate both the magnitude and direction of the field.
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