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