Amp, volt, watt: what’s the difference?

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Amps measure current, volts measure the strength of the flow, and watts are the total power released by a circuit per second. Ohms measure resistance. Understanding these terms is important for electrical work and evaluating electric bills.

Amps, volts, and watts are all ways to measure different aspects of electricity. An ampere, or amp (A or I, for current), is the amount of current in a circuit, while voltage (V) is the current flowing through the circuit, and watts (W) are the total electrical power power released by the circuit per second. One watt equals one volt times one amp, which can also be expressed as

1 W = 1 V × 1 A

A common analogy used to illustrate these terms is that of a garden hose. Amps represent the speed of the water as it flows through the pipe, while volts represent the strength of the flow, and horsepower represents the total amount of water flowing out of the pipe per second.

Related to Ohm
Another closely related measurement is the ohm (Ω), which is a unit of electrical resistance. Going back to the garden hose analogy, if the hose has a larger diameter, it will be able to flow through more water. A circuit with a high degree of resistance, expressed in ohms, is capable of carrying fewer amperes than one with lower resistance, regardless of voltage. If a high voltage meets a high resistance, the amount of current possible in the circuit will be very low: not much water will pass through a narrow tube, no matter how high the pressure. People often express the relationship between current and resistance as Ohm’s law:
A – V/O
In electrical circuits

Scientists use all of these measurements when working with electrical circuits. In their most basic form, electrical circuits consist of a positive- and negative-terminal voltage source, such as a battery; load; and two wires connecting the two. When a current (A) leaves the negative terminal of a voltage source (V), it flows to the positive one through the wires. If it encounters a load in between, such as a motor or light bulb, it passes through it, releasing power (W), in the form of light or work. The load also provides resistance (Ω), which causes the current to flow more slowly.

Practical applications

Understanding how these terms relate to each other can be helpful both in performing basic electrical work and in determining whether an existing electrical panel can support another appliance. While the watts are changeable, the voltage is usually fixed, with the US having a standard of 120 volts. An appliance that uses a large amount of current, such as an electric stove, may need to be plugged into a separate circuit with a higher voltage. This is because it requires a higher wattage, which means it draws more current per unit of time than other appliances, so it needs more voltage. Without the higher voltage, it wouldn’t work, because it would be starved of the current it needed to be able to function.

Understanding the relationship between various electrical terms can also help consumers evaluate their monthly electric bills. Electricity consumption is measured in watts, or watt hours, and electric utilities measure and bill consumption in kilowatt hours, which is the equivalent of 1000 watts of power for one hour. Many households use hundreds of kilowatt hours every month.

The number of kilowatts billed to each household is linked to volts and amperes. The volts remain constant, but the amps change according to the current demand. When people turn on more appliances or run them for longer periods, they increase the demand for electricity, which in turn increases the total watts consumed. By running fewer appliances or switching to more efficient devices that require less current, people can reduce the number of kilowatts consumed and reduce energy bills.

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