Electric Power

With Great Power…

Why do we care about power? Power is the measurement of energy transfer over time, and energy costs money. Batteries aren’t free, and neither is that stuff coming out of your electrical outlet. So, power measures how fast the pennies are draining out of your wallet!

Also, energy is…energy. It comes in many, potentially harmful, forms – heat, radiation, sound, nuclear, etc. – ,and more power means more energy. So, it’s important to have an idea of what kind of power you’re working with when playing with electronics. Fortunately, in playing with Arduinos, lighting up LEDs, and spinning small motors, losing track of how much power you’re using only means smoking a resistor or melting an IC. Nevertheless, Uncle Ben’s advicedoesn’t just apply to superheros.

Covered in this Tutorial

  • The definition of power
  • Examples of electric energy transfers
  • Watts, the SI unit of power
  • Calculating power using voltage, current, and resistance
  • Maximum power ratings

Suggested Reading

Power is one of the more fundamental concepts in electronics. But before learning about power, there might be some other tutorials you should read first. If you’re not familiar with some these topics, consider checking out those tutorials first:

What is Electric Power?

There are many types of power – physical, social, super, odor blocking, love – but in this tutorial, we’ll be focusing on electric power. So what is electric power?

In general physics terms, power is defined as the rate at which energy is transferred (or transformed).

So, first, what is energy and how is it transferred? It’s hard to state simply, but energy is basically the ability ofsomething to move something else. There are many forms of energy: mechanical, electrical, chemical, electromagnetic, thermal, and many others.

Energy can never be created or destroyed, only transferred to another form. A lot of what we’re doing in electronics is converting different forms of energy to and from electric energy. Lighting LEDs turns electric energy into electromagnetic energy. Spinning motors turns electric energy into mechanical energy. Buzzing buzzers makes sound energy. Powering a circuit off a 9V alkaline battery turn chemical energy into electrical energy. All of these are forms of energy transfers.

Energy type converted Converted by
Mechanical Electric Motor
Electromagnetic LED
Heat Resistor
Chemical Battery
Wind Windmill


Electric energy in particular, begins as electric potential energy – what we lovingly refer to as voltage. When electrons flow through that potential energy, it turns into electric energy. In most useful circuits, that electric energy transforms into some other form of energy. Electric power is measured by combining both how much electric energy is transferred, and how fast that transfer happens.

Producers and Consumers

Each component in a circuit either consumes or produces electric energy. A consumer transforms electric energy into another form. For example, when an LED lights up, electric energy is transformed into electromagnetic. In this case, the lightbulb consumes power. Electric power is produced when energy is transferred to electric from some other form. A battery supplying power to a circuit is an example of a power producer.


Energy is measured in terms of joules (J). Since power is a measure of energy over a set amount of time, we can measure it in joules per second. The SI unit for joules per second is the watt abbreviated as W.