wrote in message
oups.com...
It reminds me of many years ago when my ten year old
son said he would like to learn electronics. When I started with the
math and electrical laws, he soon lost interest

I don't mean this as a cut, but as constructive criticism.

Perhaps you didn't put it the right way. Attention spans aren't what
they used to be.

There is more to it than this but when I have to explain Ohm's law to
the electronically ignorant I use headlights.

Standard headlights were 36 watts. When you use two of them what do you
pull ? Of course you pull 72 watts. Why ?

Because the lights are 4 ohms. You have 12 volts from the battery, and
each one of these lights pulls 3 amps.

Volts are a potential between two conductors, it is a measurement of
something physical. Yes man invented the volt, but not what it
measures. An amp is a current flow, also physical and measurable.

The Ohm is a different thing, it expresses a ratio between volts and
amps.

If you have a 4 ohm headlight, it pulls 3 amps off of 12 volts because
12 divided by 4 is 3, when you simply hook two of these together they
pull 6 amps.

Watts is` the product of volts and amps. At 12 volt and 6 amps (3X2)
you are pulling 72 watts from the battery.

With em hooked together, they must total 2 ohms.

That means they pull 6 amps from the 12 volt source, and 12 volts X 6
amps is 72 watts.

Watts means heat, and as a switch in the wall, you need both to have
watts. If the switch is on there is current (amps) but no voltage.
Therefore there are no watts making heat. If the switch is off there is
voltage, but no current. It takes both.

Therefore the switch is kinda inert, if it is working properly. When a
switch that's off starts passing current, or a switch that's on allows
a voltage drop there is a problem.

Bulbs, motors and whatever else have voltage and current at the same
time, not switches.


I always thought the math was boring, if someone had started me off like
that I'd have likely lost interest too. Instead I was given a pile of bulbs,
batteries, wires, switches and went from there experimenting. Later I had
the green electronics book from Radio Shack and learned more basic stuff
there and experimented further with parts salvaged from broken equipment. It
wasn't until fairly recently that I started reading up on all the math, at
which point I can already apply it and it's a lot more interesting.