Does back electromotive force affect motors?
395873
The back EMF that must be protected against is often called inductive kick. It's a voltage spike that happens when you interrupt the current flowing through an inductance such as a solenoid or relay coil. The diode is more to protect what's connected to the coil (and probably what interrupted the current to the coil) such as a switching transistor or a set of contact points. The diode is connected across the coil and its polarity is such as to short out the spike. This always works out not to short the current away from the coil when current is flowing.\nMost motors and pumps being AC, a diode can't be used for such protection although the inductive kick can still occur. Surge suppressors are used instead.
256930
dba_gregg is correct.\n\nThe gravity pulls the front while the back is still supported by normal reaction force. Thus a torque is acting so as to rotate the bus with the front down. The angular momentum produced is conserved and the bus begins to rotate about the free axis passing through its centre of mass.
269793
electric fields are energy fields that exist around charged particles. now if you bring another charged particle into an electric field, it experiences a force. it can be either repulsion, for similar charges or attraction for opposite charges.\n\nThis force called the electrostatic force is what causes pieces of paper to stick to your sweater, and is the same force that drives electric motors.\n\nNow if you bring two charged sheets close, like described in the given problem, they attract or repulse each other. You are simply being asked to find the force.\n\nIf you consider two small pieces of sheets, the math for calculating the actual force is quite complex, especially at the edges. So for toy problems, like the ones used for teach basic principles, the charges are always "point charges" where the charged body does not occupy any volume or "infinitely large" like the sheets above. The only reason to consider something hypotheical like that is to keep the math simpler.\n\nNow when you have an infinitely large sheet, how do you measure the charge on it? if a small area of the sheet holds x Coloumbs of charge, the total charge is infinity. so again for the math, we use the charge per unit area. It turns out the forces *are* dependant on the charge per unit area and not the entire charge.\n\nNow the forces calculated also end up having the units Newtons per unit area.\n\nDoes that answer your question? Or do you want me to work out the problem too ? :) Let me know\n\n===========================================================\nI am not able to send you a message.. send me your email address\n===========================================================
648293
This is a magnetic flywheel.  The spinning magnets will induce a voltage across the coil of wire.  If you draw current from the wire, that current will induce a magnetic field which will exert a torque on the magnets, slowing them down.  The total electrical energy you can get out of the system will never exceed the initial kinetic energy of the rotating magnets.\n\nThe thing slowing down the magnets is not friction, it's an electromagnetic force, and even if you eliminate friction completely, the magnetic torque will spin down your magnets quite handily as soon as you start extracting energy from the system.
505249
no.its the force produced due to the movement of other particles(electrons).so..
280023
Short answer: The electromagnet is not doing work; if the motor is not stalled, it is doing work.\nSaturation occurs at some field intensity per unit core area. The bigger the core the more energy in the saturation field. Field energy is a function of current times number of turns in the coil. So in an electromagnet with a large core, more ampere-turns are used to make a higher-energy field. Theoretically it should take no electric power to maintain an electromagnetic field, because no mechanical work is being done. In fact superconducting electromagnets use exactly zero power. \nTo be using 90 watts, a small motor must be either doing mechanical work or stalled. The small armature core can sustain only a much less energetic field than the electromagnet. A magnetic field does work when it moves something against an opposing force. This energy loss reduces the field energy, and it takes electrical energy to restore the field.\nWhen the motor is stalled by too high a load, things work differently. No work is done and the winding may draw a lot of current and overheat. This is because the armature is designed for efficiency at speed but not stalled. It has a low-inductance winding (one with fewer turns and higher current) which can reverse polarity more easily, and two reversals are needed each revolution. Under no load, the armature runs at high speed and generates a "back-EMF" that results in almost no current drawn.
107875
Limit the load current.\nEDIT: This is often done by adjusting the stator field current if it's a generator with an electromagnet (not permanent magnet) field.
604852
Here are a couple of web sites that approach this in different ways. \n\nhttp://www.circletrack.com/techarticles/84199/\n\nhttp://www.diracdelta.co.uk/science/source/e/n/engine%20excitation%20mechanisms/source.html\n\nHope these help.
1049136
the chances are that if the motor has only one capacitor ( capacitor run only) then the run capacitor is faulty and if the motor happens to be spinning in one direction it will get up to speed in that direction. Answer buy a new capacitor. if the motor has two capacitors (capacitor start/run) the chances are the motor has serious problems because the rotation of the motor is dependent on the the terminal connections.
721433
Edit: Perhaps I should revamp my answer to provide a clearer (actual) answer, that explains exactly what plays a role and, in effect, why I am right. I also added a couple sources you should read (in case you don't believe me ;-).\n\nAs asked at the first source (which has very good information about electric motors), "How can I make the motor spin faster or slower?". The answer is that it has to do with the power of the magnetic field. Because electicity is magnetic, you can either effect the speed by using a more powerful magnet or a more powerfully magnetic electrical current.\n\nTo quote Wikipedia about what a volt is, "The volt is the SI derived unit of electric potential difference". To truly understand what the "electric potential difference" means, you must first better understand the volt. The volt is a measurement of electromotive force (emf) and is just defined in terms of amperes and watts.\n\nAn amp is the constant current which produces a force equal to 2x10^-7N per meter, when travelling across two parellel wires one meter apart. It is one coulomb of charge per second (Q/t). It is a base unit upon which other units of electicity are defined (such as the volt).\nA watt is the unit of power equal to one joule of energy per second (P=W/t).\n\nHmm. Power? Power of a magnetic field? So how can you get more power in your circuit? If your power source is not rated by power output, then you can figure out the power using convertion:\nA=W/V=C/s\n\nIf you want a higher wattage, you can increase the voltage (electrical potential) or the ampage (current) or both. Or you can increase the charge - the amount of electricity (coulombs).\n\nSo the fact remains that voltage is *not* directly related to the speed of a motor. It can be directly converted in a way that makes it useful for that purpose, but any number of other things can be done to increase the power - the real goal you are looking for.\n\nThe answer is a definite "No." and a half-assed "Yes.".\n\n\n---Original Answer---\nNo. You might want to read more about the electric motor ( http://en.wikipedia.org/wiki/Electric_motor ) and magnetic properties of electricity ( http://en.wikipedia.org/wiki/Electromagnetism ). Also see the definitions of volt ( http://en.wikipedia.org/wiki/Volt ), watt ( http://en.wikipedia.org/wiki/Watt ), and amp ( http://en.wikipedia.org/wiki/Ampere ).
354996
Gee .. been a while.  If I remember correctly the magnetic field is perpendicular to the electrical field.  Thus around the two wires the magnetic fields move in the same direction and combine, producing a net attractive force.\n\nIf the currents go the opposite direction, the forces repel.\n\nSee the link below for a more detailed explanation and pictures:
347555
Depends also if it is muscle or fat.  The muscle can overcome the inertia & air friction.
547508
No. \nThe system is static and the sum of the forces equal zero, but there definately are forces flowing through the bar.  Replace the bar with a piece of plastic and then what happens.  The system is no longer in equilbruim, becomes dynamic and the plastic gets torn to shreads.  The same would be true if say you used a piece of wire.  Just because something is not moving does not mean there are no forces flowing through it.
1139618
Yes for instance your nervous system is an electrical system and electricity is effected by electric magnetic pulls.
697205
Yes, but to a smaller degree than when on the ground.\n\nThe inertia  and the weight of the wheel will have an effect as you change speed and gears.  This is not real "rolling resistance" but has a similar, but smaller effect.\n\nIf you are on a bike stand and rotate the pedals at 60rpm in the lowest (speed) gear, then change to the highest gear, you will see more   "resistance" until the wheel is at its new higher speed.  Then you will see some resistance to maintaining that speed and cadence.  This will be more than resistance in the lowest gear, and more pronounced the heavier the rear wheel.
611013
Oh good grief.  If it's anything like what I've just done it'll include velocity, centrepetal forces, magnetic fields, friction, gravity, forces generally, working out the mass of something and the speed at which it will fall, balances with pivot points, static electricity, AC & DC electricity, transformers, vectors and so on and so on.  It's quite hard but it's maths based so if you like maths, you should be ok.  I wish you luck.
179401
Large inductive motors running at low loads cause wasteful power use due to reactive effects.  Some plants control this by ensuring thhat motors are properly sized or run fully loaded or perhaps they add large capacitors to balance the reactive effects of the induction motor.