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The Kid's doing a science fair project which is diagrammed as follows:




The power source is two nine volt batteries. The lights are all 2.5 volt lights, three in parallel and three in sequence.

We can't get all six batteries to light up at the same time (though the circuit's good) We can get the lights to light up in the series no problem, and we can get the parallel side to light up if we take some of the light bulbs out.

Would a bigger battery do it, or would that cause light bulbs to explode?

**Edit, diagram labeled with lots of letters in case you want to tell me where I should be adding more batteries, or something....

***Double Edit, [livejournal.com profile] siliconshaman, no adding nuclear reactors for bonus points.

Date: 2009-03-08 08:58 pm (UTC)
From: [identity profile] ladyqkat.livejournal.com
Darn, I was going to suggest an itty-bitty black hole or plasma star.

Date: 2009-03-09 12:04 am (UTC)
From: [identity profile] jaxomsride.livejournal.com
Is a ZPM allowed?
Is it cheating having the first 3 powered by one battery and the next 3 powered by the other?
i.e. does it have to be the batteries in series?

Date: 2009-03-09 01:14 pm (UTC)
ext_74: Baron Samadai in cat form (Default)
From: [identity profile] siliconshaman.livejournal.com
Awwwww!!!!

The thing to remember is that lightbulbs are also resistors, electricity is like water in pipe, it'll flow though the pipe that offers the least resistance.

This means the power is flowing though the serial bulbs first, which is why those light up, then it hits the first parallel bulb, flows though that, and carries on. It won't flow though the others.

Simply adding more power won't make a difference. You have to 'balance' both sides of the circuit.

I think if you move wire I-J so it's now I-K, and the wire A-M so it's now A-N it should work.

If that doesn't then you'll have to rewire it as follows:
Move the battery wire A-M so it connects A-I.
Run a new connection from M to C
[this bit requires some experimentation]
Disconnect the wire J-I at the I end, and try it in points G and E and see which causes the parallel circuit to light up.

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