Among all the possible applications of electromagnetic induction, there is no doubt that the most important ones relate to the operation of generators and electric motors. These devices are present in everyday life and are a crucial component of practically all sectors of society. While electrical generators produce practically all the electrical energy in the world, converting mechanical energy into electrical energy, motors convert this electrical energy into facilities for our practical lives.
By the end of you will understand how magnetic induction underpins the operation of these devices. Hello everyone, welcome to Verve Cientifica. Before you start, subscribe to the channel and activate your bell.
This will put you in touch with our content, where we explain the basic laws that govern the world, which is undoubtedly brilliant for your personal development. POWER CONVERTERS If you repeatedly move a magnet closer and further away from a conducting coil, the direction of the voltage induced in that coil will alternate. The frequency with which you do this will be exactly that of the alternating voltage that is induced, which in turn will be equal to the frequency of the variable magnetic field inside the loop.
To induce an alternating voltage it is more practical to move the coil than to move the magnet. And this is typically done by simply rotating the coil in a stationary magnetic field. When you do this, what you have is an arrangement called an electrical generator.
The construction of a generator is, in principle, identical to that of an engine. These two devices look the same, they both transform energy from one form to another, but the roles of input and output are reversed. In a motor, electrical energy is the input and mechanical energy is the output.
In a generator we have the opposite, mechanical energy is the input and electrical energy is the output. MAGNETIC FLOW ABOUT A ROTATING LOOP When we analyze the physics of a motor and a generator you will see that they both operate under the same physical principle: electrons in rotating motion experience a force that is perpendicular to both their speed and the magnetic field in which they are located. immersed.
We can better understand this by analyzing the electromagnetic induction cycle. Note, that when a loop of wire is rotated in the magnetic field, the number of magnetic field lines within the loop varies. When the plane of the loop is perpendicular to the field lines, the number of field lines is maximum, and the magnetic flux is maximum.
As the loop rotates, it cuts the lines, leaving many of them outside its area, thus, fewer lines cross it and the flow is reduced. In the limit, when the plane of the loop is parallel to the field lines, no line crosses the loop and the magnetic flux is zero. ELECTRICAL GENERATORS If you have a flashlight that works by turning a crank, you have a generator in your hand that converts the energy in your hand into electrical potential energy.
The energy to be converted in an electrical generator can be supplied by different sources. Like falling water from a hydroelectric dam, expanding steam in a coal-fired power plant, wind in the blades of a mill, or the output of a small gasoline engine powering a portable generator. In all cases, the principle of operation that I mentioned just now is the same: mechanical energy is used to make the conductive coil rotate immersed in a magnetic field and thus produce an electromotive force of movement, in accordance with the law of Induction.
. Note that the linear movement of a metal bar through a magnetic field would also result in a moving force, but obviously it would not be feasible to produce an electric current in this way, as the bar would have to move over increasingly greater distances. That's why the most practical and ingenious way is to use a coil that can be rotated in the presence of a magnetic field.
Imagine a coil rotating in a magnetic field. Here we consider a coil with a single turn, just to simplify. But in practice, the wire is usually wound in several turns around an iron core, which drastically enhances the magnetic effects.
This coil/core structure is called the armature and is typically the armature that rotates inside a generator. But let's go back to our elementary model. Note that in it the loop is in contact with metallic rings, attached to each end of the wire that makes up the loop.
It is this contact that allows the induced electromotive force to be transferred to the external world. As the loop rotates with omega angular velocity, the electromotive force produced in it is given by Faraday's law. Considering the oscillatory nature of the magnetic flux, which assumes maximum values e.
minima passing through a zero value, we can write the alternating voltage of a rotating coil in terms of a sinusoidal function. Note that the electromotive force induced in the coil alternates in sign, which means that the current in the coil alternates in direction. This is why this type of generator is called an alternating current generator.
The angular frequency of the coil movement is what stipulates the nominal frequency of 60 Hz, which is the frequency of Brazilian electrical systems. A hydroelectric plant is an excellent example of generating electrical energy. First, the gravitational potential energy of water held behind a dam is converted into kinetic energy as the water moves down through pipes at the generating station.
Then, the kinetic energy of the falling water is used to turn the turbines. Each turbine rotates the coil of a generator in a strong magnetic field, thereby converting mechanical energy into electrical current in the coil. Through a transmission line, electrical energy is delivered to homes, factories and cities, and is converted into other forms of energy more convenient for practical use, such as light in lamps, heat in kitchen appliances and baking and working on various household appliances.
In fact, these appliances that carry out work have their energy coming from electric motors. ELECTRIC MOTORS While in an electric generator the shaft connected to the rotor is driven by an external mechanical force, in an electric motor the shaft rotates due to the magnetic force that is developed between the motor armature and the field. In other words, while in a generator the current is PRODUCED in the winding, in a motor, the current is SUPPLIED to it.
In an electric motor, the loop carrying current in a magnetic field suffers a torque that tends to make it rotate. If this loop is mounted on a rotating shaft, it is possible for magnetic torque to be applied to the outside world. In practice, the magnetic torque on the loop causes it to rotate.
Once it reaches a critical angular position, it continues its movement, passing through this position due to its inertia. At this point, the incoming alternating current reverses its direction, which leads to a reversal of the torque on the loop, causing it to rotate further away from the critical position. The next time the loop reaches this critical angle, the current reverses again, causing the loop to continue rotating clockwise.
The result of this is that the axis will continue to rotate continuously in the same direction. Note again that this process is exactly the reverse of what occurs in a generator: instead of doing the work to rotate a coil and produce an electric current, as a generator does, a motor uses an electric current to produce a rotation in a coil. , which then does work.
You might think that an engine, in a way, is nothing more than a generator that works in reverse. If a car is powered by an electric motor, its engine can act as a generator when it helps to slow down the car during braking. This results in a more efficient means of transport , because some of the car's kinetic energy, which normally dissipates as heat during braking, can now be used to recharge the batteries and increase the car's range.
This is precisely the famous KERS energy recovery system, which was used for some time in formula 1 cars. COUNTER-ELECTROMOTIVE FORCE When discussing Lenz's law, I mentioned the curious case of Joseph Newmann, a lunatic American inventor who believed have found a source of unlimited energy. Newmann filed a major lawsuit in the United States in the 1980s against the patent office, claiming to have invented an unlimited source of energy.
An engine that ran on just a small battery. He considered that how a current loop produces a magnetic field at its center. So, for two turns, the induced magnetic field will be doubled, for three turns, the field triples, and so on.
So he assumed that it was possible to create as large a magnetic field as you want just by adding more turns to the current supplied by a single battery. While this is possible, there is a big price to pay for it, which Newmann obviously didn't realize. When a motor is operating, two sources of electromotive force are present.
One is the applied electromotive force that provides current to drive the motor. The other is the induced electromotive force. As the coil rotates in a magnetic field, the changing magnetic flux induces an electromotive force, which must be consistent with Lenz's law, which says that this electromotive force always acts to reduce the current in the coil.
In the design of electric motors, this electromotive force is called "counter-electromotive force" or "reverse electromotive force". We know that the higher the motor speed, the greater the flux change through the coil and the greater the counter-electromotive force that appears in the system and which tends to reduce the current supplied. As this electromotive force has opposite polarities to the input voltage, the resulting electromotive force in the circuit will be the difference between the applied voltage and the induced electromotive force.
Thus, when you connect a battery, according to Lenz's Law, the increasing magnetic field will induce an opposite electric current due to the inverse electromotive force. This implies that the more turns the motor has, the more the current will be prevented from circulating and the longer it will take for the magnetic field to reach its full value. This is one of the aspects of energy conservation applied to electromagnetism.
If the motor operates without mechanical load, the electromotive force will reduce the current, but to a value that is still large enough to overcome the energy losses inherent in the motor's operation. Now, if the engine runs under a very heavy load, the engine will stall and will no longer turn. Thus the lack of an electromotive force can lead to a dangerously high current in the motor.
Disregarding this counter-electromotive force, imposed by Lenz's law, was Newmann's big mistake, who obviously was unable, even with the support of the mainstream media, to get his patent approved for his illusory energy machine. This video ends here! If you liked this content, subscribe to the channel and leave a like.
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