Sciencemadness Discussion Board

Very Simple Battery Demo

hodges - 26-6-2004 at 16:28

I stumbled upon this idea while trying to come up with the simplest possible demonstration of an electric cell.

Magnesium by itself has enough electrical potential to light a red LED. Simply touch the negative lead of an LED to a piece of magnesium ribbon, and touch the positive lead to either a carbon rod, or else a small piece of copper pipe fitting from the hardware store. When these plates are immersed in salt water, the LED lights - brighter as the plates are immersed further. No need to fuss with multiple cells as is normally required when using zinc.

I got slightly better results with the carbon rod than with the copper, but both work. I measured around 1.8 volts using the carbon rod and 1.7 volts using the copper. Theoretically the copper should add a couple tenths of a volt to the cell whereas the carbon should be neutral. I suspect the reason the carbon rod works better is either that the copper contains impurities that may have a negative vs. positive potential.

Zn vs Cu

Magpie - 26-6-2004 at 17:54

I once offered my services for "Engineers' Week" for one day at a local junior high school. I tried to tell the 8th grade students what engineers do and what careers were available.

My demo for the class was very similar to yours except I used a sharpened 3/4" Cu pipe and a Zn coated strip of sheet metal for electrodes. I pushed these into an orange to form the electrolyte bridge. I also lit a red LED, getting a little over a volt IIRC. :)

Funkerman23 - 4-5-2012 at 09:02

Quote: Originally posted by LanHarjochee  
I want to buy these battery-operated LED fairy lights to drape over my wooden notice board or metal headboard. My parents say they will start a fire... Do you think they would? Why/ why not? If yes, are there any lights that are similar that I can buy that aren't a fire hazard?
Not a chance, those diodes( the LEDS) won't even get above room temp if ran at their rated voltages. and to further this the voltages used to light the LEDs isn't anywhere near enough to create a hot enough spark. you'd blow out most of the diodes long before and IF( and this is a big IF) there was a spark it wouldn't do much but catch your eye. In short there is no way that a led light string can do much of anything except light up. How this relates to the OP I don't know.

[Edited on 4-5-2012 by Funkerman23]

Agecer - 27-9-2012 at 03:23

Quote: Originally posted by Funkerman23  
Quote: Originally posted by LanHarjochee  
I want to buy these battery-operated led tube to drape over my wooden notice board or metal headboard. My parents say they will start a fire... Do you think they would? Why/ why not? If yes, are there any lights that are similar that I can buy that aren't a fire hazard?
Not a chance, those diodes( the LEDS) won't even get above room temp if ran at their rated voltages. and to further this the voltages used to light the LEDs isn't anywhere near enough to create a hot enough spark. you'd blow out most of the diodes long before and IF( and this is a big IF) there was a spark it wouldn't do much but catch your eye. In short there is no way that a led light string can do much of anything except light up. How this relates to the OP I don't know.

[Edited on 4-5-2012 by Funkerman23]


I believe LED is the best technology when it comes to lighting

[Edited on 28-9-2012 by Agecer]