QUESTION: a couple of permanent magnets will hold back each other forever will with great push not difficult while making a permanently magnetically levitated platform In which does the ability to execute the job come from?
ANSWER:One of the truths of electromagnetism is that a magnetic field never does work, you never get work (create energy) directly from a magnetic field. The explanation is always that an induced electric field is what actually does the work. The case of permanent magnets is more complicated than most to try to explain explicitly, so I will give a similar example, taken from the classic text Introduction to Electrodynamics, David Griffiths, Prentice Hall Publishers. In the figure to the right there is a constant current in the loop as indicated and there is a magnetic field pointing into the page in the cross-hatched area. The upward force on the loop is just right so that the weight, mg, levitates. Of course, right now, no work is being done since the force is not moving the mass. But, suppose that the field is now increased so the upward force now exceeds mg. Now the mass starts rising. The magnetic force is doing the work, right? Wrong! Before you increased the field the direction of the electrons’ velocity was to the left (don’t forget the electrons go in the direction opposite the current). But, when the loop starts moving up, the electrons now also have a component of their velocity upward and that gives rise to a component of the force on the electrons which is to the right; but this would reduce the current which we have stipulated to be constant. So the battery in the circuit (which is not shown but has to be there if there is a steady current) has to supply more energy than before and that is where the work done on the rising coil comes from the battery. This is really just Faraday’s law, an induced back EMF in the loop arises because of the changing flux. I know this is not the exact question you asked, but, trust me, all “where does the energy come from when magnetic fields frequently carry out really works” questions boil down to similar explanationsan electric field you forgot to think about.
QUESTION: why does the fresh new digital force transform on the magnetized push giving particular velocity towards the observer we.elizabeth. just how try these dos forces figure dependent?
‘s the newton’s 3rd rules of motion are violated here
ANSWER:In reality, digital and magnetized sphere commonly something else, he could be manifestations of just one community, the fresh new electromagnetic job. Once you change from physique regarding mention of more swinging frame, you replace the mix of new digital and magnetized parts of those areas. Such as for example, a place charge at peace enjoys a natural digital industry; but if you notice it from a moving figure away from source, it’s each other an electronic and you will magnetic occupation. It’s way too inside it to show the details right here. Why that people nonetheless mention electronic and you will magnetic areas for the basic physics programs would be the fact, usually, it grabbed a long time to see their associations. Brand new electromagnetic field is not a great vector industry, it is an effective tensor job, an industry that has more than 3 elements.
The fresh new electrostatic forces was reddish and so are equal and you can reverse
QUESTION: an enthusiastic electron moving perpendicular to help you a charismatic field knowledge lorentz force , here you will find step but where’s new “equal and you can contrary” impulse force .
ANSWER: The field will be created by a current someplace and also the “reaction force” could well be on that cord. Although not, one to push isn’t necessarily equal and you may opposite to your push towards the electron. Newton’s third legislation, given that coached when you look at the primary physics, is not really undoubtedly real and you can magnetic pushes, because they are speed mainly based, are the most effective analogy showing it. The newest contour reveals a couple self-confident charge moving with velocities revealed by the black colored vectors. New magnetized force felt by the particle moving horizontally are no since the career there (due to the most other fees) is actually no. Industry due to the charges swinging horizonatlly things upwards aside of the monitor, and so the magnetic push (blue) on the other fees is to try to just the right. The internet push on each particle try shown in the environmentally friendly and you can he’s neither equal neither opposite. Newtonian aspects takes on the forms into the electromagnetism and you can that which you nevertheless all hangs along with her, however you need are the time and you will energy densities regarding brand new fields. This is certainly means outside the range with the webpages to address.
