In the last few days I’ve been asked a couple of times to comment on a video that’s been going round – on the Guardian and Edinburgh talk107 radio.
The miracle video shows someone soaking an onion in an energy drink, sticking the USB cable into the onion and voila! Enough charge to listen to all of Yes’s Tales from Topographic Oceans, including studio run-throughs. Or so it claims.
Here’s the infamous video:
Amazing eh? Pity it’s a hoax. While it’s based on some basic electrochemistry, there are a few things that just don’t add up in this video. And now for the science bit…
The main problem is the USB cable – two electrodes of the same material will not spontaneously make a current, in any vegetable, whether it’s been soaked in energy drink or Ambrosia custard. When you plug your iPod into your computer/the wall to charge, a potential is set up from the power source.
To get this potential from the onion, there needs to be a chemical reason for the ions to flow and create this potential, which there certainly isn’t in the hoax video. This is explained far better than I could over at the Naked Scientists, but I’ll provide a Jon Edwards masterpiece to help the explanation here.
Setting up a cell with an onion
The basic idea is that you need different electrodes – one more “reactive” than the other. When there’s a chance for, say, zinc metal to become zinc ions, it’ll jump at it – giving off electrons at the same time. Copper, on the other hand, would prefer to be a metal and will use those electrons to reclaim some copper ions the fruit or vegetable in question has stolen from it. The energy drink provides the “electrolyte”, a chemists’ word for “solution with ions”; this helps the zinc/copper ions move more easily. The electron flow between the electrodes is the electrical current these experiments use to charge the iPod.
My other gripe with the video is that he’s set the iPod up on what is clearly a box, with the USB cable looped underneath the iPod. My guess is that he has two cables – one going from the iPod to a charger hidden in the box, and another coming from the box into the onion. Looping the two behind the iPod completes the illusion – but he can’t fool us chemists 