# Electronics Primer: Introduction

The field of electronics offers a powerful set of tools for obtaining accurate numerical data. Instead of just saying that there is a difference between two things (color, brightness, charge, etc.), electronic devices allow you to measure precisely how big the difference is.

Electrons and Charge

The word electronics is derived from "electron." Electrons are sub-atomic particles with a negative charge. The unit for electric charge is the coulomb. One coulomb equals the charges of 6.24 billion billion (1018) electrons. A single electron has a charge that is too small to measure in most electronic devices, so scientists use coulombs as a more useful way to describe charge.

Multimeters

The basic outputs for electronic devices are voltage, current, and resistance. Inexpensive and sensitive devices, called multimeters, can measure each of these. If you can devise a way for the output of your experiment to be in the form of voltage, for example, you can use a multimeter to get precise numerical data. For more information about using a multimeter, see the Science Buddies Multimeter Tutorial.

Voltage

The definition of voltage is: the measurement of the potential for an electric field to cause a current in a conductor. An electric field "pushes and pulls" electric charges, so if you put an electron in an electric field, it will move. The movement of charged particles is a current (more about current below). The essential point is that the voltage is a measure of how strongly charged particles are being pushed and pulled by an electric field. The symbol for voltage is V.

Consider a simple flashlight with two D batteries. Each D battery has a voltage of 1.5 V. By putting two 1.5-V batteries together, the total voltage equals 3 V. This voltage is high enough to power a lightbulb. When you turn the flashlight on, the voltage difference causes electrons to flow through the lightbulb, making it shine. The electric field provides the energy to move charged particles through wires (electrical conductors) and through the lightbulb.

Voltage can be direct (DC) or alternating (AC). In DC voltage, the voltage does not alternate. If you graph the voltage of a 9-V battery vs. time, for example, you will have a straight line at a value of 9 V. Alternating current flips back and forth between positive and negative. If you make a graph of AC current vs. time, it will alternate from positive to negative, often in the form of a sine wave. Voltage is supplied to a circuit by a battery or other power supply.

Current

Current is a measurement of how much charge moves through a circuit in a given period of time. In the case of the flashlight, the current through the lightbulb is a measurement of the amount of electric charge flowing through the lightbulb in a given time.

The symbol for current is I. The symbol for the unit of current, the ampere, is A. The precise definition of an ampere is: the current produced by the flow of one coulomb per second. Use "I" when referring to current (as in Ohm's law, discussed below) and "A" when referring to the amount of current.

DC current is produced by DC voltage and AC current is produced by AC voltage.

Resistance

Electrons flow through materials in response to a voltage, creating a current. Some materials, such as copper, have very low resistance, so the electrons flow freely—they are good conductors. Some materials have intermediate resistance, such as the semiconductors used to make transistors. Semiconductors might have a threshold value for the voltage that will cause a current to flow, for example. And some materials, such as rubber, have high resistance and are used as insulators to separate charges.

The symbol for resistance is R. The unit for resistance is the ohm, which has the symbol Ω, and is the capital letter "W" in Greek.

Ohm's Law

Ohm's law relates voltage, current, and resistance, mathematically. Ohm's law can be written as: $V = IR$ . In words, Ohm's law states that the voltage in a component in a circuit equals the current through the component, times the resistance of the component.

Electronic Circuit

An electronic circuit is a closed path formed by the interconnection of electronic components through which an electric current can flow. You might find it helpful to compare an electronic circuit to a circuit in which water flows.

• Voltage in the electronic circuit is like the pump in the water circuit—it provides the push to make things go.
• Current in the electronic circuit is like the rate (in liters per second, for example) that water flows in the water circle.
• And resistance in an electronic circuit is like a constriction in a hose in the water circuit. An electronic resistor impedes the flow of electrons, just as a constriction in a hose impedes the flow of water.

For additional electronics information, visit these Science Buddies pages: