Three things they should have taught in Engineering 101, Part 2: How to visualize electrical components

Darren Ashby -February 19, 2013

Note: The following is adapted from the book "Electrical Engineering 101, Third Edition" by Darren Ashby (Newnes).

[Part one explains how, by understanding unit math, you can solve nearly any problem.]

Mechanical engineers have it easy. They can see what they are working on most of the time. As an EE, you do not usually have that luxury. You have to imagine how those pesky electrons are flittering around in your circuit.

We are going to cover some basic comparisons that use things you are familiar with to create an intuitive understanding of a circuit. As a side benefit, you will be able to hold your own in a mechanical discussion as well. There are several reasons to do this:

  • The typical person understands the physical world more intuitively than he understands the electrical one. This is because we interact with the physical world using all our senses, whereas the electrical world is still very "magical," even to an educated engineer—much of what happens inside a circuit cannot be seen, felt, or heard. Think about it. You flip on a light switch and the light goes on; you really don't consider how the electricity caused it to happen. But, drag a heavy box across the floor, and you certainly understand the principle of friction.
  • The rules for both disciplines are exactly the same. Once you understand one, you will understand the other. This is great, because you only have to learn the principles once. In the world of Darren we call EEs "sparkies" and MEs "wrenches." If you grok1 this lesson, a "sparky" can hold his own with the best "wrench" around, and vice versa.
  • When you get a feel for what is happening inside a circuit, you can be an amazingly accurate troubleshooter. The human mind is an incredible instrument for simulation, and unlike a computer, it can make intuitive leaps to correct conclusions based on incomplete information. I believe that by learning these similarities you increase your mind's ability to put together clues to the operation and results of a given system, resulting in correct analysis. This will help your mind to "simulate" a circuit.

Physical Equivalents of Electrical Components
Before we move on to the physical equivalents, let's understand voltage, current, and power. Voltage is the potential of the charges in the circuit. Current is the amount of charge flowing2 in the circuit.

Sometimes the best analogies are the old overused ones, and that is true in this case. Think of it in terms of water in a squirt gun. Voltage is the amount of pressure in the gun. Pressure determines how far the water squirts, but a little pea shooter with a 30-foot shot and a dinky little stream won't get you soaked.

Current is the size of the water stream from the gun, but a large stream that doesn't shoot far is not much help in a water fight. What you need is a super-soaker 29 gazillion, with a half-inch water stream that shoots 30 feet. Now that would be a powerful water-drenching weapon. Voltage, current, and power in electrical terms are related the same way. It is in fact a simple relationship; here is the equation:

voltage * current = power         (Eq. 1.1)

To get power, you need both voltage and current. If either one of these is zero, you get zero power output. Remember, power is a combination of these two items: current and voltage.

Now let's discuss three basic components and look at how they relate to voltage and current. There are three fundamental components in virtually every circuit, resistor, inductor, and capacitor. Figure 1.1 shows what they look like. Getting a picture in your head of how they interact with electrical charges is fundamental to gaining insight about what is happening in an electronic circuit.

FIGURE 1.1: The three basic components of a circuit.

1 Grok means to understand at a deep and personal level. I highly recommend reading Robert Heinlein's Stranger in a Strange Land for a deeper understanding of the word grok.
2 Or moving as we learned in Chapter 0.

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