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.
0.1V = 1/10 volt
.001V = 1/1000 volt = 1 milliVolt.
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
1.2A = 1200 mA
.2A = 1/5 amp = 200 mA
1mA = 1/1000 amp = .001 amps
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.
1000 ohms = 1k ohms = .01m ohms
10,000 ohms = 10k ohms = .1m ohms
1m ohm = 1000k ohms = 1,000,000 ohms
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.
Voltage (V), current (I), and resistance (R) are related by Ohm's Law. There are three different forms of
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:
V = 9
How about if you connect the same battery through a 1k resistor?
R = 100
I = V/R = 9/100
I = .09 amps (90 milliamps)
V = 9
Or what if you just use a piece of wire (R = 0!)
R = 1000
I = V/R = 9/1000
I = .009 amps (9 milliamps)
V = 9
What if you use a 12volt battery and a 100 ohm resistor?
R = 0
I = V/R = 9/0
I = infinity!!! (divide by zero error!!!)
V = 12
R = 100
I = V/R = 12/100
I = .12 amps (120 milliamps)
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:
V = 5
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.
I = .02
R = V/I = 5/.02
R = 250 ohms
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?
V = 12
How about a 24V motor that's drawing .5amps?
I = .5
P = VI = 12 * .5
P = 6 watts
V = 24
How Stuff Works has a nice page called
"What are amps, watts, volts and ohms?" with more info.
I = .5
P = VI = 24 * .5
P = 12 watts
I'm so excited! Take me to Part 2!!!