![]() So, centripetal acceleration is equal to "v squared" over "r". The charge on the electron, divided by "r squared", is equal to the mass of the electron times the centripetal acceleration. Is the same magnitude as the charge on the proton,īut it's a negative value. Write that in here, "q1", "q1" is the charge on a proton, which we know is elemental charge, so it would be positive "e". The electric force is a centripetal force, keeping it in circular motion, so we can say this is the We're talking about the electron here, so the mass of the electron times the acceleration of the electron. We know that Newton's Second Law: force is equal to the mass It's the charge on the proton, times "q2", charge on the electron, divided by "r squared", where "r" is the distanceīetween our two charges. Given by Coulomb's Law, the magnitude of the electric force is equal to K, which is a constant, "q1", which is, let's say We're gonna use it to come up with the kinetic energy for that electron. And, once again, we talkedĪbout the magnitude of this electric force in an earlier video, and we need it for this video, too. This is a centripetal force, the force that's holding that electron in a circular orbitĪround the nucleus here. ![]() There's an electric force,Īlright, so this electron is pulled to the nucleus, So we know the electron isĪlso attracted to the nucleus. We're doing the Bohr model, there's a certain radius associated with where that electron is. We have one proton in the nucleus for a hydrogen atom, using the Bohr model, and we know, we know, that if The negative charge, the velocity vector, it'dīe tangent at this point. Going this way around, if it's orbiting our nucleus, so this is our electron, Alright, so we need to talk about energy, and first, we're going to try to find the kinetic energy of the electron, and we know that kineticĮnergy is equal to: 1/2 mv squared, where "m" is the mass of the electron, and "v" is the velocity. Of derivation using physics, so you can jump ahead to the next video to see what we come up with in this video, to see how it's applied. And so we're gonna be talkingĪbout energy in this video, and once again, there's a lot A representative value can be calculated with the following data.- If we continue with our Bohr model, the next thing we have to talk about are the different energy levels. Parameters left unspecified default to values for a 12 gauge copper wire carrying 10 amperes.Ĭalculation of the density of free electrons in a metal like copper involves the basic physical data about the metal, plus the fact that copper provides about one free electron per atom to the electrical conduction process. This slow average drift speed for electrons is tiny compared to the average electron speed associated with its internal energy.Ĭalculation note: Any of the properties of the wire can be changed. The drift velocity is V d = x10^ m/s = cm/hour. If the wire diameter is mm then the area is A = x10^ m 2. The drift velocity of electrons in a copper wire can be calculated from It is the change or "signal" which propagates along wires at essentially the speed of light. Charge carriers in Hall effectĪlthough your light turns on very quickly when you flip the switch, and you find it impossible to flip off the light and get in bed before the room goes dark, the actual drift velocity of electrons through copper wires is very slow. In many substances, electric conduction is not just free electron movement. One way to detect which kind of conduction is taking place is with the Hall effect, which gives a different polarity for the Hall voltage for positive and negative charge carriers. There are significant differences in the way they conduct. In semiconductors, for example, you sometimes have electrons which are mobile, and sometimes have deficiencies of electrons, called " holes" which are mobile. In other applications of electric current however, the identification of the charge carriers is not so simple. Debate continues about this practice, but the physical nature of the charge carriers in copper is fairly straightforward. Nevertheless, treatments of electric circuits usually use conventional current, as if positive charges were moving. HyperPhysics***** Electricity and Magnetismįor electric current in a copper wire, the charge carriers are the mobile electrons and the positively charged copper ions are essentially stationary in the metal lattice. Since electric charge is quantized in discrete multiples of the electron charge, it is instructive to look at electric current as the movement of multiple microscopic charge carriers with a drift velocity in a conductor. ![]() ![]() Microscopic View of Electric current Microscopic Electric Current ![]()
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