What is power?

Power is the amount of electrical energy transformed into another type of energy (heat, light or work) per second. Power is an important concept because it is what allows our electric circuit to do something. For example, if we created a circuit with a battery and a resistor, the resistor will convert the electrical energy to heat (or thermal) energy. All resistors also have a maximum power rating that they can handle therefore to ensure that we do not damage the resistors in a circuit we will need to know how to calculate power. Power is calculated by multiplying the voltage by the current and is measured in Watts.

Most of the low-cost resistors that we can get from online retailers are rated at 1/4 (or 0.25) Watts so we will assume that the resistors we are using for the projects in this book are rated at that 1/4 Watt. Now let's say in our project we are running a voltage of 10V across a 100 Ohm resistor, do you think the resistor will be able to handle it? To figure this out, the first thing we need to do is to calculate the current using Ohm's law. We will use the formula I = V/R to calculate the current (I = 10V/100 Ohms) and come up with a current of 0.1 Amps. We can now use the formula P = V*I to calculate the power (P=0.1A * 10V) which would equal 1 Watt, which is four times what the resistor is rated for, therefore the resistor will get very hot and may even get damaged.