Some tacky arts/crafts stuff with the kids (physics help)!

Gazz · World Chat Champion Joined: 19 May 2009 Karma :

We are currently doing some arts and crafts stuff with the kids and had the idea to put some lights behind a picture to make it more 'realistic'.

Had the idea of maybe a landscape picture with a sun in the background and putting a yellow LED behind it which would look the mutt's nuts at night time! Dance!

However I have no idea or how this could be achieved. Had the thought of using those little bulbs that come behind the dash in a car and wiring it up to a AA battery of something? Would this work? Maybe an engine management light bulb since they are sun-coloured.

Any help much appreciated.

I took Biology and Chemistry at school and the extent of my physical knowledge is wiring the odd plug.

I do however own a soldering iron. Wink

And a AA battery.

Beehive Bedlam · World Chat Champion Joined: 28 Oct 2013 Karma :

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stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Go to the local pound shop/discount store and get some tacky solar-powered garden lights.

Dismantle them, chuck away the plastics and you'll have a battery, a small solar cell and an LED. Put the LED and battery behind the picture, put the solar cell on the front.
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ScaredyCat · World Chat Champion Joined: 19 May 2012 Karma :

Nobby the Bastard · Harley Gaydar Joined: 16 Aug 2013 Karma :

duhawkz · World Chat Champion Joined: 03 Dec 2006 Karma :

MahatmaAndhi · Traffic Copper Joined: 10 Jun 2015 Karma :

Why not get a clear LED and where the cut out of the sun is, put a yellow transparent film over it?
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bamt · World Chat Champion Joined: 14 Dec 2013 Karma :

Buy an amber/orange LED from ebay or Maplin - e.g. https://www.maplin.co.uk/p/3mm-yellow-led-n70kg
https://www.maplin.co.uk/p/5mm-yellow-led-n71aj

Then you'll need a resistor, depending upon what battery you are using.

So, for example, the 3mm LED above says Forward Voltage 2 V
Forward Current 30 mA.

If you run it off two AA batteries, you'll have a voltage of 3V, so you need to drop 1V across the resistor.

Ohms Law - V=IR, or R=V/I
In this case, the voltage drop you want is 1V, the current is 0.03A (30mA), so R=1/0.03
you want a 33 Ohm resistor. I'd be tempted to run it at a bit less current (less bright), so a 47 Ohm would work.
https://www.maplin.co.uk/p/metal-film-06w-47-ohm-resistor-m47r

the 5mm LED above says Forward Voltage 2.8 V, Forward Current 30 mA

As above, you want to drop 0.2V, so you'd want a 6.67 ohm to run it at full brightness.
Again, I'd actually be tempted to run it at 20mA instead, so a 10ohm
https://www.maplin.co.uk/p/metal-film-06w-10-ohm-resistor-m10r

You can run the same calculations for if, e.g. you wanted to run off a 9v battery.

Solder the resistor to one leg of the LED (doesn't matter which) and connect to your batteries. If you connect the wrong way around it won't light up, but won't be damaged.

Total cost about 40p.

Alternatively go to the pound shop and buy some cheap battery powered christmas lights.

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Screw that. If you're going for physics, you need to power the LED by lemons. Get that interest in there early so they're not as crap at it as their Dad when they grow up. Wink

The internet says you'll need 4 lemons to light an LED. Green LEDs use less power.

Stick a bit of copper (thick copper wire, a piece of copper pipe/whatever) and a piece of zinc (galvanised nail) into a 4 lemons. Connect the copper on one to the zinc on the next one until you have a row of them with a piece of copper on one end and a piece of zinc on the other. Connect your LED to these. If it doesn't light up, connect it the other way.

Fuck yeah, science.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

Mawsley · Traffic Copper Joined: 07 Apr 2016 Karma :

Chinaboy · World Chat Champion Joined: 13 Jan 2007 Karma :

Lord Percy · World Chat Champion Joined: 03 Aug 2012 Karma :

Lord Percy · World Chat Champion Joined: 03 Aug 2012 Karma :

On the topic of actually getting kids into science:

I just bought one of these: Arduino electronics starter kit

Comes with a 145 page PDF full of lessons right from the basics so anyone can get one and give it a go.

Might be a little too complicated for kids actually but definitely worth a shot for any man-child who wants to have a play. Basically the electronics version of mechano.

WD Forte · World Chat Champion Joined: 17 Jun 2010 Karma :

I ran an lcd watch on two spuds for a fortnight
using zinc nails and copper wire
I was going to suggest using CR button cells to power the leds
but they can be horribly nasty, if not fatal if swallowed by little ones
so a pair of AAs ( 3V) may be safer and no series resistors needed

You could probably use a local poundshop to pick up cheap gadgets and toys to hack for battey holders and leds

Pre crumpled baco foil held about 1 cm behind the pic with leds shining up the gap can have a pleasing backlight effect
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