Volts, Amps, and Ohms

Volts, amps, and ohms are three basic units of electrical measurement. Voltage is the potential or electrical pressure difference between two points in an electrical circuit and is measured in volts. For example, the voltage of a typical car battery is 12 volts. This is the potential difference or electrical pressure between the positive and the negative battery terminal. It can be measured with a voltmeter or multimeter set to read voltage. Voltage can be measured by hooking a voltmeter across two parts of a circuit where you want to measure the difference in volts. It might be easier to understand if you think of voltage as the electrical force or pressure in a circuit or battery, just like the water pressure that exists in the bottom of a full tank of water or a home plumbing service.

The ampere, or amp, is the unit used to describe how much current or how many electrons are flowing at a given point in a given amount of time when work is being performed—for example, when a lamp is operating. An amp is a measure of the number of electrons flowing past a given point in 1 second. An amp is equal to 6.28 billion billion electrons past a given point in 1 second. Yes, billion billion is correct. To say it another way, think of a pile of 1 billion electrons. One amp would equal the number of elections in 6.28 billion of those piles travelling past a given point in a circuit in 1 second. That is impressive! No wonder we can’t see them! And just to get you thinking, a starter motor may draw about 200 amps. Amperage, or current flow, can be thought of as a faucet being turned on and water flowing. Each drop of water is like an electron. Current flow is measured in amps by placing an ammeter into the circuit so that the current flows through the meter.

The ohm is the unit used to describe the amount of electrical resistance in a circuit or component. The higher the resistance, the less current (amps) that will flow in the circuit for any particular voltage. The lower the resistance, the higher the current that will flow in the circuit. Using the water analogy, if you kink a hose with the water running, less water will come out of the hose for a given pressure. If you kink the hose more, more resistance will be added and even less water will flow through the hose. Lessening the kink will lower the resistance and allow more water to flow. Resistance in a simple electrical circuit works the same way.

An ohmmeter is used to measure the amount of resistance in a component or circuit. The ohmmeter pushes a small amount of current through the part being tested, so an ohmmeter is usually used on a component or wire that has been disconnected from the rest of the circuit. The amount of resistance in the component changes the amount of current that the ohmmeter can push through the component. The more current that the ohmmeter can push through the component, the lower the resistance will read on the ohmmeter.