NJM said:

Hello.

I am trying to teach myself the basics, but I am confused about ampage.

For instance, say I have a power source that is 12v at 2 amps. I want

to power a simple LED circuit that I found on the internet that is

designed for a 12v supply but there is no mention of the current. The

circuit is a 50 ohm resistor and 3, 3.6v ultra bright white LEDs. The

resistor value was calculated for a 25mA current using ohm's law. What

is the resistor modifying? The current or the voltage? Will this

circuit be usable regardless of the supply ampage? The voltage/current

relationship has me confused.

TIA for any insight you may be able to provide.

This has been describe in many ways .. I'll give mine, i'm sure many

will give you their own version. But to put in a simple means for now.

Picture your self wading in water (a river maybe), lets say the

water is moving 5 MPH (Voltage), and you are standing in 1 foot of

water that is moving against you (Current).

Now step in 2 feet of water. The mass that is pushing against you has

now doubled (current), the speed is still the same(speed). Of course if

you repeat this action and have a big hang over like me, when it reaches

the mid section, mass will most like go up 10 times.

The Power could be looked at as the combination of mass (current) and

Speed(Voltage) as Voltage * Current = Wattage.

using the same analogy with pipes. water moving at a set speed in all

different size pipes. the larger volume pipe will have more current of

water in it and will be able to push a heavier weight at the same speed.

Now, picture a very small pipe with water moving at high

pressure/speed(voltage). The impact on a surface could cause damage but

will not be able to push that massive area. if you have ever gotten a

High voltage arc shock of a few thousand volts with no much amps you may

have notice a pin hole or some kind of skin damage.

Now, think of a Resistor as a pipe, the lower R values would be the

same as large pipes that allow less restriction of mass and the higher

values would be like small pipes, restricting mass.

Lets say you have a volt meter(Speed of water), this meter has no

mass for the water to resist against(very small object in water), you

can get the same voltage on both sides of that resistor how ever, in the

real world, the resistor will be connected to an item like the LED's.

These LED's are lets say the blocking mass, much like you standing in

the water. the water will slow down as it finds its way around you.

This slowing down of water (speed)= Voltage will be seen by

your volt meter when testing the speed (voltage) at that point.

Now you can increase this flow by using a smaller resistor how ever,

this is like increasing the volume of water which puts more pressure

against you in the water. this pressure is being converted to energy

that you're expending keeping your self balanced, much like the LED

emitting light.

At some point, there will be too much mass for you to handle and you

will fall in the water much like the LED going to LED haven!

Now lets touch base a little on Speed (Voltage) even though you can

have high voltage with no mass behind it, it's does not mean it's safe.

Take a thin sheet of plastic and put it in the river with slow moving

water but a large area. The plastic sheet will most likely handle that

how ever, placed in fast moving stream of water (Voltage) with no Volume

(current) and it can blast a hole in the sheet. just picture this as

the maximum voltage a component can handle before it breaches or shorts

out from over voltage(Speed)..

Ok, I've gave my explanation. Years ago i used this example teaching

the basics back when they use to have Cub, Boy,Eagle scouts etc... I can

say that many of them ended up in a electrical/electronic couriers.

Hope that gave you some insight!.

"I'm never wrong, once i thought i was, but was mistaken"

Real Programmers Do things like this.

http://webpages.charter.net/jamie_5