The Relay Races
Knowing that magnetism and electronics are related is a very important lesson. Just how important will become evident in the next few lessons, as we will be discussing the interaction of electricity and magnetism in greater detail. Let's review some of the things we have learned:
Note that the electrons from the negative side of a battery will attract toward the positive side, if the two are brought electrically close enough to be allowed to do so. This typically happens by connecting a wire, lamp, or some other electrical device between the two electrical poles.
Does electricity move from positive to negative, or from negative to positive? This is a good time to discuss the fact that because we can not truly see the electrons in motion, but can only study their effects, there are 3 differing schools of thought on this subject, all of which have some merit.
With this thought in mind, we can control the physical movement of a permanent magnet, by controlling the voltage going through a given electromagnet. If we attach a battery to an electromagnet in such a way that it has the opposite polarity of a nearby permanent magnet, it will pull the permanent magnet closer to it. If we then swap the wires going to the battery, the electromagnet will change its polarity, and the permanent magnet will be pushed away from it.
If we physically attach the permanent magnet to a plunger, we can control the movement of the plunger in and out using electrical current. In this way, we use electric current to push a button, pull a lever, open or close a valve, or any number of other tasks.
Because magnets attract ferrite based metals, we can also use electricity to control the physical movement of iron. In the examples given to the right, we are using electric current to move a type of reed switch. These are handy for allowing us to use a small amount of current to, for example, turn on a motor which needs a very large amount of current.
Now would be a good time to show a schematic diagram and picture of a relay. The diagram to the left is an exact duplicate of the make contact relay circuit represented by the above picture. The break contact relay schematic symbol would be similar, except the contacts would be connected. Keep in mind, that not all schematic symbols are standard. You may see variations of schematic symbols over the years, but they will all be understandable and descriptive of the function of the component.
Below is a picture of a relay
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