The concept of the electromagnet is something you’ll need to know. If an electric current has the ability to generate a magnetic field around a magnet – this is referred to as an electromagnet. When the current gets turned off, the magnetic field, too, is turned off. The magnet we’re referring to usually presents itself in the form of an iron core, with coiled wires insulating the magnet. The electric charge makes the magnetic field of the magnet much more powerful – something that finds use in electrical devices ranging from motors, generators, loudspeakers and medical equipment. The benefit is you can control the magnetic field by altering the amount of electrical charge you apply to the coils of the magnet.

The electromagnet is also the foundation for another vital electrical device known as the transformer. This device is effectively composed of two electromagnets side-by-side, with its function involved in processes such as distributing electricity, or even changing AC voltages for power electricity lines. This valuable contribution is just one notable benefit since the development of the electromagnet. Other equally valuable devices that depend on electromagnetism include motors and generators. Motors and generators are very simple to understand: with a motor converting electrical energy into kinetic energy, and a generator converting kinetic energy into electrical energy. Thus, the motor and generator act reciprocally – reversing functions through the same process.

What we call an electric motor is, in fact, more of a magnetic motor. The motor is composed of two types of magnet: a rotor and a stator. The stator is the equivalent of an ordinary stationary magnet, while the rotor is the equivalent of an electromagnet. The rotor spins inside the stator due to the repulsion between the magnets. After all, every magnet has both a positive and negative pole – and it’s these poles that repel between the rotor and that stator. The energy created by the rotor is produced through movements caused by the electromagnet in the stator, as it’s the movement of the rotor that produces kinetic energy. So, in this sense we can understand how electrical energy from the electromagnet is converted into kinetic energy – the very essence of what a motor is supposed to do.

For your ASVAB Electronics Information test, you will need to familiarize yourself with various electrical symbols. The definitions we described earlier are only part of this process, as circuits are often pictorially represented. You will need to recognize these pictorial forms and be able to tell what’s going on in these circuits. In this section, we take you through several of the most common electrical symbols to appear on the test, explaining the details you need to consider in your study. The best approach to memorizing these symbols is simply to analyze the construction of the image in question – as the picture is often drawn “giving away” the function due to the way it’s represented.

We haven’t come across several of these definitions yet, such as capacitor. A capacitor is a device used in electronics to briefly store electricity. We should be familiar with the voltmeter and ammeter – as they are devices used to measure the quantity of volts and current in the circuit. The resistor, as we saw, insulates against the flow of electricity, while the energy source can be found in the battery. AC current is primarily found in complex systems such as home wiring, whereas DC current is used for everyday home devices such as phones, TV’s, and laptops. It’s worth noting that batteries always produce DC current. A diode, one the other hand, is similar to a resistor but differs in one notable respect – it has low resistance to current from one direction but high resistance to current in the other. In this sense, the diode exhibits what’s known as asymmetric conductance.

It might take some practice, but learning these symbols is absolutely fundamental to success in your ASVAB Electronics Information test – as they serve to illustrate in simple form what’s going on in sometimes quite complex electrical systems. In the next section, we’re going to take a look at some of the more basic types of circuit – understanding how systems work with the myriad of electrical devices we have hitherto just described.

The electrical current we have thus far been describing, along with the symbols used to represent this process; can only exist in the presence of an electrical circuit. This circuit allows the movement of negatively charged electrons. There are some devices, such as resistors, which negate this transfer of charge while other devices, such as switches, can immediately halt the transfer of charge. In this section, we’re going to analyze two basic types of circuit you’ll need to understand for your ASVAB Electronics Information exam: series circuit; parallel circuit. We’ll go through each of these circuits in detail below – you should pay attention to the direction of electrical charge at all times.

We can see an example of a series circuit below. In this type of circuit, electrons are free to move throughout the entire circuit, unless the switch is off of course. While current is equal along all points of the series; voltage will drop as current passes through each device along the circuit. We can see these devices represented as lamps A, B, and C, below. If this series was supplied by a 14V battery – a single lamp volt-drop must also be 14V. Similarly, given the series below has three lamps, the volt-drop is still maintained at 14V. The problem, of course, with the series circuit is that once you cut off supply to one of the lamps, all of the lamps will be denied access to the current. This problem is overcome should you use what’s known as a parallel circuit.

In the parallel circuit, we can see the structural difference of how current can flow around the system. If we were to cut off one of the lamps, current would still have the capacity to reach the other lamp. This overcomes the limitation we described with series circuits. This means that the lamps in the parallel circuit receive the same voltage at all times. We can summarize the difference between series and parallel circuits as follows: current is the same at all points along a series circuit whereas voltage is the same at all points along a parallel circuit. Remembering this one difference can go a long way to grasping the fundamentals of these differing circuits.

There are two very different ways of calculating resistance in both the series and parallel circuits. For the series circuit, we need only sum the total value of the resistance. So, say a series circuit had load resistance values of 8Ω and 4Ω – the total resistance would be 12Ω. Straightforward! But, the same cannot be said for calculating resistance for parallel circuits. To work this out, we need to take the reciprocal value of the combined resistance and solve the calculation thereon. To understand this method, take a look at the following example:

In the next step, we need to add the fractions 1/12 and 1/8. To do this, we need to find a common denominator between 12 and 8. Such a number is 24 – the lowest common denominators for the two values. Let’s not forget the top number in a fraction is known as the numerator and the bottom number is referred to as the denominator. To add fractions such as this, we need to convert both numbers to similar form. If we can change the 12 and 8 both to 24, then we only need to add the numerators to add the fractions in a simple and effective way. Take a look:

This now means that:

Now, we simply need to cross-multiply:

Given that resistance is measured in terms of Ohms, the total resistance of this particular parallel circuit is 24/5 Ohms. So, calculating total resistance isn’t too challenging as long as you’re aware of two things: if it’s a series circuit you merely sum total each resistance, and if it happens to be a parallel series, you find the reciprocal of each resistance value and solve the equation for R. With this in mind, we can advance onto the penultimate section of our ASVAB Electronics Information study guide – semiconductors.

Apart from insulators (such as rubber and plastic) and conductors (such as aluminum and copper), there’s a third class of material we’ve yet to discuss – semiconductors. As the name suggests, the semiconductor can act either as a conductor or an insulator, depending on certain conditions. The main semiconductor material in use is silicon. Silicon is ubiquitously used in computing, particularly when it comes to computer memory and logic. An example of a semiconductor device is the transistor. This is a small device used in the amplification of electronic signals and electrical power, as well as having the ability to switch such signals.

Earlier, we saw an example of a second type of semiconductor device – the diode – the device that has the capability of allowing current flow in one direction while simultaneously blocking it from the opposing direction. Given the ubiquity of semiconductor use in this day and age, you should have some familiarity with the concept, as well as being able to list examples – such as the transistor and diode – while detailing what function the semiconductor will elicit for these devices. Along with insulators and conductors we saw at the beginning of our ASVAB Electronics Information study guide, the semiconductors complete the main types of material device you’re expected to know.