Electronics Workshop for Artists

Voltage, Current, Resistance, Power

voltage (V): the difference in electrical potential between two points. Voltage is measured in "volts" and is usually indicated by a V. In the water metaphore, voltage is the distance from the bucket to the ground. A higher bucket = a higher voltage.

current (I): the volume of electron flow. Current is measured in "amps" and is usually indicated by an A. Small currents are common, and are specified as milliAmps, or mA (1/1000 amp). In the water metaphore, current is the volume of water that is flowing. More flow = higher current.

resistance (R): something that impedes the flow of electrons. Resistance is measured in ohms, and is usually indicated by an Ω (Omega) symbol. Large resistances are specified in kilo-ohms (k) (1,000 ohms) or megaOhms or (m) (1,000,000 ohms). In the water metaphore, resistance is determined by the size of the hole in the bucket. A bigger hole = a smaller resistance.

power (P): a measure of the amount of work done in an electrical system. Power is measured in watts and is usually indicated by a W. In the water metaphore, power is the amount of work done by the turning water wheel.

Ohm's Law

Voltage (V), current (I), and resistance (R) are related by Ohm's Law. There are three different forms of the equation: Using ohm's law is easy. You pick an equation to use based on the value you're trying to find. Let's say you have a 9volt battery and you connect the + and - terminals through a 100 ohm resistor and you want to know how much current is flowing. You will use the I = V/R form: How about if you connect the same battery through a 1k resistor? Or what if you just use a piece of wire (R = 0!) What if you use a 12volt battery and a 100 ohm resistor?

What if you want to limit the amount of current flowing through a circuit to say, 20mA, and you've got a 5v power supply. What size resistor would you need? We'll use the R = V/I form:

So you can see that a given voltage across a given resistance will result in a proportional flow of current. If the resistance is too small (like 0 ohms!) You have a short circuit. That's what would happen if you just touched one terminal of a battery to the other. Looking at ohm's law again, you can see that if R = 0 then you've got a divide by zero problem...And so a super high current. That's bad. Short circuits tend to make the magic smoke come out of things. Don't do that.

Power Law

Power is derived from the simple equation: That is, power is equal to the voltage times the current. So if you have a 12v motor that's drawing .5amps, how much power are you using?

How about a 24V motor that's drawing .5amps? How Stuff Works has a nice page called "What are amps, watts, volts and ohms?" with more info.

I'm so excited! Take me to Part 2!!!