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You’ll find electromagnets in just about every modern electrical device. They’re what allows you to speak on your mobile phone – both the microphone at the bottom of the handset and the speaker and the top rely on electromagnets to do their job. You’ll also find them in other, totally different applications – from the MRI scanner at your local hospital to the starter motor in your car. But exactly how is it that electromagnets work, and why are they so useful? Let’s take a look.
What is electromagnetism?
Whenever electricity passes through a length of wire, it generates a tiny electromagnetic field in the surrounding air. This is because each of the atoms in the wire are pushed in the same direction by the stream of electrons. There are several ways in which we can make this effect more pronounced. By increasing the current, we can create a larger and more powerful field. Similarly, by wrapping the wire into a tight coil, we can enhance the effect further – with smaller, tighter coils producing a greater magnetic force. Wrap these coils around an iron core, and you’ll in effect create a magnetic device from nothing.
One immediate use for a device like this is in handling high-current circuits. A traditional switch, which mechanically brings two contacts closer to one another until they touch, can have undesirable side effects if the current is sufficiently high. A dangerous arcing spark might occur, as the electric potential will be enough for electricity to leap over the gap as the contacts near one another. In a sensitive environment, like the fuel-soaked interior of a car’s engine, this is problematic.
Electromagnets can be used to limit the danger. They can exert a force that brings the two contacts together so fast that the air cannot be heated. This electromagnet is part of a low-current circuit which can safely be completed using the mechanical ignition switch in your car’s interior.
How does an electromagnet create a motor?
One of the most useful applications for an electromagnet is to turn electrical energy into kinetic energy. This is typically achieved using an electric motor, which can in turn be used to push and pull the windows of your car up and down, or to lower and raise your seats. Electric motors arrange a coil of wire between opposite magnetic poles. By pulsing the magnets on and off, changing the polarity with each switch, it’s possible to drag the central shaft of the motor around and around. These devices can be found in the starter motor of your car – and they draw a high current. Different manufacturers will use different starter motors, so it’s important you match any replacement to your vehicle. You’ll find Ford, BMW and Volkswagen starter motors available online.
What about generators?
Of course, as well as turning electrical energy into kinetic energy, an electromagnet can also be used to do just the opposite. The generator within a wind turbine, for example, makes use of this principle: induction. A magnet moving near a coiled wire will generate an electric current inside that wire. In your car, there’s a special device called a generator which translates the motion of the crankshaft into electrical energy which can be used to keep the car’s battery topped up. The more the magnet inside the generator moves, the more current will be generated.
Generators, suffice to say, can only do their job while the car is in motion. Thus, if you leave an electrical device running, such as you car’s headlights, then the battery will run flat and you might have difficulty getting the thing started. If your generator should develop a fault, then you might encounter the same problem: the electrical devices in your car will steadily fail, until the starter motor dies. You can buy alternators online to suit a range of vehicles, should yours fail.
These devices tend to come in two forms. There are dynamos, which are often found in older vehicles and put out a stream of direct current. Then there are alternators, which you’ll find in newer vehicles. Alternators put out alternating current, which must be translated into direct current before it can be considered useful. This is done using a special device called a rectifier, which uses a series of diodes and capacitors to firstly shear off the bottom portion of the alternating signal, and then smooth out the resulting waveform until it’s a nice, steady stream of DC which can be used to charge the battery.