Ohms, Amps, Volts and Watts

December 13, 2017 by Ben Stowe, CTS

Electricity is the lifeblood of the systems we run, so having a basic understanding of it can be very helpful for engineering and operating reliable systems. Moreso, it can be essential in troubleshooting them when things go wrong.

While there are a great many electrical terms, four fundamentally important ones are Ohms, Volts, Amps and Watts. These are all units of measure and they are intertwined in electrical relationships known as Ohm’s Law and Watts Law.

Ohms law tells us that Ohms are equal to volts divided by amps, while Watts law tells us that Watts are equal to Volts x Amps. Using these two basic formulas, we can calculate to find 2 unknown values if we know any other 2.

Named for Georg Simon Ohm, the Ohm is a unit of measurement for the resistance in an electrical circuit. A device with greater resistance will have a higher ohm value associated with it. Many times, we see ohm values for loudspeakers. While this correlates to impedance, which is similar but fundamentally different than resistance, for the purpose of this article, we’ll treat them as one and the same. Therefore, an 8 ohm loudspeaker presents more resistance to an amplifier than a 4 ohm loudspeaker does.

In honor of Alesandro Volta’s work, we have the Volt. Voltage is the electrical potential of the circuit. It is present whether electricity is flowing or not. A good example of this is a battery, or an outlet. At an outlet in the wall there is approximately 120 volts available, whether a device is plugged into it or not. Think about this like water pressure. It’s present even when the faucet is turned off.

Amps, short for Amperes, named for Andre Marie Ampere, measure the current, or electrical flow of a circuit. They are also the typical value found on circuit breakers and fuses. The greater the flow of electricity, the greater the value in amperes. Because of Watts law, we know that to create 1000 watts from a 120 volt power outlet, we need 8.33 amps of current.

Watts, named for James Watt, measure electrical power. Many times we see watts listed as a measurement for a loudspeaker. While they measure how much electrical work is being accomplished, they are not good representatives of how loud or otherwise effective it is. No more so than using wattage to compare the brightness of an incandescent lamp and an LED lamp. Wattage can be helpful when matching amplifiers to loudspeakers, or when determining what the appropriate size circuit to supply a system is. Using Watts law you can determine the number of amps necessary at your circuit breaker when you know the Watts and Volts.

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