# 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 current.

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.

## Ohm's Law

Voltage (V), current (I), and resistance (R) are related by Ohm's Law. There are three different forms of the equation:
I = V/R
V = IR
R = V/I
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
R = 100
I = V/R = 9/100
I = .09 amps (90 milliamps)
How about if you connect the same battery through a 1k resistor?
V = 9
R = 1000
I = V/R = 9/1000
I = .009 amps (9 milliamps)
Or what if you just use a piece of wire (R = 0!)
V = 9
R = 0
I = V/R = 9/0
I = infinity!!! (divide by zero error!!!)
What if you use a 12volt battery and a 100 ohm resistor?
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
I = .02
R = V/I = 5/.02
R = 250 ohms
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:
P = VI
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
I = .5
P = VI = 12 * .5
P = 6 watts
How about a 24V motor that's drawing .5amps?
V = 24
I = .5
P = VI = 24 * .5
P = 12 watts
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!!!