{"id":89,"date":"2014-07-01T14:05:34","date_gmt":"2014-07-01T18:05:34","guid":{"rendered":"https:\/\/itp.nyu.edu\/physicalcomputing\/?page_id=89"},"modified":"2022-06-20T06:35:18","modified_gmt":"2022-06-20T10:35:18","slug":"electricity-the-basics","status":"publish","type":"page","link":"https:\/\/itp.nyu.edu\/physcomp\/lessons\/electronics\/electricity-the-basics\/","title":{"rendered":"Electricity: the Basics"},"content":{"rendered":"\n

<\/span>Introduction<\/span><\/h2>\n\n\n\n

Adapted from Understanding Electricity<\/a><\/em>
In order to understand how electronic circuits work, and how to use them to build physical interfaces to digital systems using microcontrollers, there are some basic terms, relationships, and components that you need to know about. What follows is a brief introduction to those terms.<\/p>\n\n\n\n

You won’t need to know anything about electricity or electronics to understand this page.<\/p>\n\n\n\n

<\/span>Definitions<\/span><\/h2>\n\n\n\n

Electricity<\/strong> is the flow of electrical energy through conductive materials.  An electrical circuit<\/strong> is made up of two elements: a power source and components that convert the electrical energy into other forms of energy.  We build electrical circuits to do work, or to sense activity in the physical world.<\/p>\n\n\n\n

Sensors<\/strong> are components that convert other forms of energy into electrical energy so we can read the changes in those other forms. Switches, knobs, light and motion sensors all fit in this category.  Actuators<\/strong> are components that convert electrical energy into other forms. Light bulbs, motors, LEDs, and heaters are all actuators.<\/p>\n\n\n\n

Electronics<\/strong> refers to reading changes in electrical properties as information.  For example, a microphone changes sound pressure waves in the air to a changing electrical voltage. This process of changing one energy into another is called transduction<\/strong>, and devices that do it are called transducers<\/strong>. Much of the technical work of physical computing is about figuring out what forms of energy a person is generating, and what kind of transducer you can buy or build to read that energy. In order to do that, though, it’s necessary to understand a few things about electricity. Following are a few terms we’ll use to refer to electrical properties and components. After that, we’ll talk about the important relationships between some of these terms.<\/p>\n\n\n\n

Voltage <\/strong>is a measure of the difference in electrical potential energy between two points in a circuit. It is measured in Volts<\/strong>.<\/p>\n\n\n\n

Current <\/strong>is a measure of the magnitude of the flow of electrons through a particular point in a circuit. It is measured in Amperes<\/strong>, or Amps<\/strong>.<\/p>\n\n\n\n

Resistance <\/strong>is a measure of a material’s ability to oppose the flow of electricity. It is measured in Ohms<\/strong>.<\/p>\n\n\n\n

To understand the relationship between voltage, current, and resistance, imagine an avalanche of snow on a mountain. The height of the mountain is analogous to the voltage; the higher the mountain, the more potential energy the falling material has.  The amount of snow and rocks in the avalanche is analogous to the current.  And the steepness of the mountain is analogous to the resistance: the steeper the mountain, the less it will resist the flow of the snow and rocks. We’ll define this a bit more formally below.<\/p>\n\n\n\n

Every circuit has to have a source<\/strong> of electrical energy and a load<\/strong> that uses the energy.All of the electrical energy in a circuit has to get used by the load. The load will convert the electrical energy to some other form of energy, A circuit with no load  is called a short circuit<\/strong>. In a short circuit, the power source feeds all of its power through the wires and back to itself, and either the wires melt (if you’re lucky), or the battery and the components blow up.<\/p>\n\n\n\n

Figure 1 is a very basic circuit, consisting of a lamp, a pushbutton, and a battery. The battery is the source and the lamp is the load. The electrical energy coming from the battery is converted to heat and light energy by the light bulb. All of the energy is used up in the process. However, if the bulb cannot take the voltage produced by the battery (for example, a 6V lamp and a 9V battery), the lamp’s filament will melt trying to transduce all the electrical energy into light and heat.<\/p>\n\n\n\n

\"One<\/a>
Figure 1. AA Battery connected to a button switch and lamp in series<\/figcaption><\/figure><\/div>\n\n\n\n

There are two common kinds of circuits:  Direct Current (DC)<\/strong>, and Alternating Current (AC).<\/strong> In a DC circuit, current always flows one direction. In an AC circuit, the direction of current flow is reversed in a regular repeating cycle.  Most of the circuits we’ll talk about in this class will be DC circuits.<\/p>\n\n\n\n

Schematic diagrams<\/strong> are diagrams of circuits that represent the electrical relationships between the components in the circuit. A schematic doesn’t \u00a0always show the spatial arrangement of the components; it’s arranged so that you can best understand the flow of the electricity. You can find a large collections of schematic symbols in SVG format, useful for drawing your own, on the Wikipedia page for “Electronic Symbol”<\/a>. An SVG collection of them in one file, convenient for editing into your own diagrams, can be found on this Wikimedia commons page<\/a>. The symbols for the components you’ll use most commonly in this class are shown below as well.<\/p>\n\n\n\n

Figure 2 show two schematics of the light bulb circuit above. In both, the important parts to note are the functional components, namely the lamp and the switch, and the power and ground terminals. In the diagram on the right, the whole circuit is shown as a loop, with the battery (marked V1) to the left of the loop. In the diagram on the left, the circuit is not shown as a loop. Instead, the power source is at the top, and the point of lowest energy, or ground<\/strong>, is at the bottom.  This diagram shows the flow of energy from the top of the diagram to the bottom. Related Video: Intro to Schematics<\/a><\/p>\n\n\n\n

\"Schematic<\/a>
Figure 2. Two schematics of a 1.5 volt battery connected to a switch and lamp in series.<\/figcaption><\/figure><\/div>\n\n\n\n

<\/span>Components<\/span><\/h2>\n\n\n\n

Conductors <\/strong>are materials through which electrical current moves freely.<\/p>\n\n\n\n

Insulators <\/strong>are materials which prevent the flow of electricity.<\/p>\n\n\n\n

Resistors <\/strong>resist, but do not totally block, the flow of electricity. They are used to control the flow of current. Current can move either way through a resistor, so it doesn’t matter which way they’re connected in a circuit. Resistors are measured by their resistance in ohms<\/strong> (\u03a9), often seen in kilohms (k\u03a9)<\/strong>. <\/strong>They are symbolized as shown in Figure 3:<\/p>\n\n\n\n

\"Four<\/a>
Figure 3. Four resistor types, from left to right: Fixed Value Resistor, Variable Resistor, Potentiometer, Photo-resistor or light dependent resistor.<\/figcaption><\/figure><\/div>\n\n\n\n

Related videos: Resistors, variable resistors, and photocells<\/a>; Potentiometer<\/a><\/p>\n\n\n\n

There are many different types of variable resistors, including:<\/p>\n\n\n\n