AC - Abbreviation for alternating current, which is voltage that flips back and forth between positive and negative.
Ampere - Unit of current (symbol: A).
Breadboard - A board used to make temporary circuits. The breadboard has metal-lined sockets for connecting electronic components in a test circuit.
Capacitor - An electronic component consisting of two conducting surfaces, separated by an insulator. It is used to store and release energy and to control high-frequency signals.
Circuit - A collection of electronic parts connected together, usually designed to perform some kind of function.
Circuit diagram - A diagram that depicts a circuit, using symbols for electronic components. Used to design and communicate circuits with other people, like a blueprint or a plan.
Closed circuit - A circuit in which current can flow through electronic components, from a point of high voltage to a point of low voltage.
Conductance - The opposite of resistance. Materials with high conductance (e.g. metals) have low resistance. The unit of conductance is siemens (S).
Current - The flow of electric charge. The unit for current is amperes (A).
DC - Abbreviation for direct current voltage, which is voltage that does not alternate.
Diode - An electronic component that allows current to flow freely in only one direction.
I - Symbol for current. The unit for current is the ampere (A).
Integrated circuit (IC) - An electronic component that contains several simpler electronic components. An IC is a miniaturized electronic circuit.
Jumper - A short length of wire used to temporarily complete a circuit or to bypass a break in a circuit.
Kilo - A prefix meaning "thousand." A 10-kΩ resistor is 10,000 ohms.
Lead - Length of wire used to make connections between components in a circuit.
Light-emitting diode (LED) - A solid-state device that has two key features: it allows current to flow in only one direction (that is the "diode" part), and it emits light when current flows through it in the "allowed" direction. LEDs are described by several specifications, some of the more important of which are:
Color of light;
Angle of light beam (for example, an LED with an angle of 15 degrees produces a more focused beam than one with a beam of 45 degrees); and
Size, usually 5 mm.
Figure 1. Light-emitting diodes come in a variety of sizes, shapes, and colors. (Wikipedia, 2008.)
Mega - A prefix meaning "million" (symbol: M). A 1-MΩ (megaohm) resistor has a resistance of 1 million ohms.
Multimeter - An instrument with several different kinds of meters. Multimeters are used to measure voltage, current, and resistance, among other things.
Ohm - Unit of resistance. The symbol for the ohm is Ω. You can make this symbol in Microsoft Word by changing the font of a capital "W" into the font called "Symbol," using the "Format" menu.
Ohm's law - V = IR, or "Voltage equals current times resistance." Example: Say a 1,000-Ω resistor has a voltage drop of 9 V. What is the amount of current that is flowing through the resistor? Plugging the numbers in yields 9 V = I amps x 1,000 Ω, so I = 9/1,000 amps (A), or 9 milliamps (mA).
Open circuit - A circuit with a gap in it that prevents current from flowing. When you turn of a light with a light switch, you open up the circuit connecting the lightbulb to the source of electricity.
Parallel connection - Current flows through two or more components at the same time. As an analogy, imagine a river splitting into two or more parallel streams, which then merge together again. The amount of current flowing through the various "streams" depends on their resistance.
Figure 2. This diagram shows two resistors in a parallel connection.
R - Symbol for resistance. The electrical resistance of an object is a measure of its opposition to the passage of a steady electrical current. Metals have very low resistance, whereas substances such as rubber and plastic have high resistance. The unit of resistance is the ohm, with the symbol Ω.
Resistor - An electronic component used to "resist" the flow of current. Resistors are used to control current in an electric circuit. The unit of resistance is the ohm (Ω). The value for the resistance of a resistor is coded by colored lines on the resistor. When they are in a circuit with a voltage supply, a "voltage drop" occurs across the resistor.
Resistors have three key features: their level of resistance, their power rating, and their tolerance. Say a resistor has a resistance of 220 ohms (Ω), a power rating of 1/4 watt (W), and a tolerance of 5 percent. The power rating tells you the limit of the power (power = current x voltage through the resistor) that the resistor can withstand without overheating. Tolerance is a measure of the resistance range. A 220-ohm resistor with a 5 percent tolerance will have a resistance in the range of 220 ohms ± 11 ohms. An electrical specification might call for a resistor with a value of 100 Ω (ohms), but will also state a tolerance, such as "±1%". This means that any resistor with a value in the range 99 Ω–101 Ω is acceptable.
Short circuit - A low-resistance connection established between two points in an electric circuit that are designed to be at different voltages. For example, connecting the positive and negative poles of a battery with a wire causes a short circuit. Because of the low resistance of the connection, the level of current can be very high, leading to excessive heat and damage to the circuit. Short circuits can cause fires and explosions if the current is large enough.
Serial connections - In a serial connection, the current flows through each component one at a time, like a river passing through several dams. The amount of current flowing through the components is equal, since they are connected "end-to-end." Compare to parallel connection.
Figure 3. In this diagram, two resistors are shown in a serial connection.
Tolerance - The range of variation permitted in an electrical component.
V - Symbol for voltage. The unit for voltage is the volt.
Voltage - A measure of the difference in electric potential between two points. A voltage difference causes electrons to flow, much like a difference in height can make water flow. The unit for voltage is the volt (V).
Winscope - A free program that lets you use your computer as an oscilloscope. It is very useful for measuring voltage vs. time data for beginner electronics projects.
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