On Feb 14, 12:04 pm, "HK" wrote:
Thanks everyone. Good information here.

This is a Grade 6 project and I was a little distressed to find that even
the basic concepts of electricity haven't been taught yet they are supposed
to build a basic circuit and working model.

For instance, my daughter assumed that to power two 6v lights, she needed a
12v power supply. Yikes.

Is Grade 6 too early to teach Ohm's Law? Should they be learning to hook up
basic circuits without learning Ohm's Law and the concepts of voltage,
current and resistance?

Some of this stuff is coming back to me. Am I correct in assuming that the
problem with wiring the lights in series is there is too much cumulative
resistance at the far end of the circuit to light the lights?

FYI, we're building a small airboat. There are four 3v LED lights powered
by 2 "C" batteries and a single 6v motor powered by 4 "C" batteries.

Aha! LED's, and not filaments. Please DISREGARD my post elsewhere in
this thread, where I ramble on about what happens when a filament is
supplied with 6V instead of the designed-for 12V.

I'm puzzled, in your original post you refer to a "12 V light". Is
that referring to these four LED's, wired in series? But above here
you are saying they are actually powered by 3V, indicating that they
are in parallel. Without a clear picture of what is going on, I'm not
sure what advice to give you.

Any suggestions on a fun followup project that will help both of us learn
more electricity concepts?

You could buy some resistors and red or yellow LED's from Radio Shack
(if you're in the U.S.). They'll also sell battery holders, and some
wires with alligator clips. You can experiment with calculating the
LED current for different resistors, and seeing how the LED dims/
brightens when you try different resistors. For a 2V red LED driven
by 3V, some resistors to try a

(3V - 2V)/(0.030 A) = 33 ohms
(3V - 2V)/(0.010 A) = 100 ohms
(3V - 2V)/(0.003 A) = 330 ohms

(Even if the LED says it is rated for 20 mA, driving it at 30 mA for 5
or 10 seconds will be okay.)

Do you have a voltmeter? You could show that the voltages across the
resistor and LED always add up to equal the voltage of the battery
(which you should also measure, don't just assume it's 1.5)

I admit these suggestions aren't as exciting as a model boat that
lights up and has a running motor, but it is a starting point to start
a 6th grader on learning some of the basics of electricity.

Regards,

Mark