Monday, June 13, 2016

Ask a Physicist: Phone Flash Sharpie Shock!

Lexie and Xavier, from Orlando, FL want to know:

"What's going on in this video? Our science teacher claims that the pain comes from a small electrical shock, but we believe that this is due to the absorption of light. Please help us resolve this dispute!"
Well, I guess this is the kind of mischief that kids are getting up to these days. Still, it's better than half the stupid "tricks" I remember hearing about in my student days. (Yeah guys, let's play the "choking game". That sounds like a blast.)


For those of you not in a position to watch the clip, the "trick" goes something like this: the person colors a black square on his arm using a permanent marker. Then, the flash "bulb" LED of a phone is held against the square as a picture is taken with the phone. The bright flash is accompanied by a sharp, stinging pain on the victim's skin, they jump a little, and laughs are had by all. (Note: if you elect to try this at home, you will probably hurt yourself, seeing as it is a process literally designed to induce pain.)
Right off the bat, I'm immediately inclined to agree with Lexie and Xavier's assessment—that it's a light-based phenomenon. The phone's flash LED is designed to put out a large amount of energy as light in a very short time. Since black-colored objects absorb visible light of any wavelength, it's not surprising that coloring your skin black and mashing it against a high-power light source might transfer a good bit of that energy to your skin, resulting in a minor burn.
BUT, in the interest of fairness to the teacher, it'd be best to settle this like true scientists—with an experiment!
First, it's important to figure out the details of your hypothesis vs. your teacher's. From your point view, it's obvious why the black ink is necessary for the trick to work on a lighter-skinned person—to absorb the light of the phone's flash and convert it to heat. What role does your teacher think the ink plays? If he thinks it's electrically conductive, perhaps using a silver sharpie—which ought to conduct electricity just as well, but which would reflect the light rather than turning it into heat—would settle the matter.

What other experiments could you design that would conclusively rule out one hypothesis or the other?

37 comments:

  1. We'd have to try it out on bare skin, without drawing anything.

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  2. this stuff hurts bad

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  3. I tried the silver sharpie;it hurts just as bad, if not worse.

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  4. does this leave a permanent mark or damage to the hand i did this and its worrying me

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    1. Yes it does. You will also find other serious symptoms. Very serious

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    2. Yes it does. You will also find other serious symptoms. Very serious

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  5. I did this earlier and died :(

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  6. We used black sharpie and phone flash - got the shock. We then used a very bright (more power than a simple laser pointer) green (532) laser and got same result, THOUGH it it took several seconds for it (the pain) to occur -suggesting heat vs an electric chock

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  7. We used black sharpie and phone flash - got the shock. We then used a very bright (more power than a simple laser pointer) green (532) laser and got same result, THOUGH it it took several seconds for it (the pain) to occur -suggesting heat vs an electric chock

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  8. This does not work. I tried it on myself and maybe felt the tiniest sensation of heat but that is it.

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  9. It shocked me and my don used green Sharpie

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  10. is it okay to do that? doesn't it effect the skin?

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  11. Used a black sharpie and my flash delayed - which resulted in sooo much pain eek. Not same as when the flash fires immediately.

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  12. Did this with a black sharpie. Flash delayed on one try & hurt soooo much more than when the flash fired first go.

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  13. It doesn't work with other black markers. So it must be electric shock.

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  14. Fun science experiment for kids! Lol. It works!

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    1. How about having someone else hold the phone - can't complete the circuit in that case.

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  15. You feel the pain be cause the circuit doesn’t complete and it is transferred into your skin and nerves

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  16. My daughter wants to do this...should I let her? Will she be safe? She is 11...will it hurt?

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    1. "if you elect to try this at home, you will probably hurt yourself, seeing as it is a process literally designed to induce pain"
      "probably hurt"
      "process literally designed to induce pain"

      Yeah, i'd say it probably hurts.

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    2. heck no! it's dangerous

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  17. One thing that occurs to me- different wavelengths can stimulate different molecules, just like a microwave oven has a wavelength tuned to excite water molecules. It seems likely the phone is radiating a wavelength that is tuned to a solvent in the sharpie ink. Especially since some people have said the sharpie doesn't have to be black. If someone has the appropriate equipment to analyze the spectrum coming off their iphone when they take a picture, it might answer the question. The cell phone radio and the wifi radio are both close to the frequency of a microwave oven.

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  18. It doesn't work and is psychosomatic. Have them do it blindfold and randomize whether the flash goes off or not. They'll be able to tell no better than chance whether there was a flash

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    1. It’s not psychosomatic in the least. Did it to my brother with a blindfold and didn’t tell him what I was doing. He definitely felt it.

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  19. The phone flash will push out more light / power if it sees a dark subject so using black will amplify the effect. However, with the phone hard up against the skin, even lighter colours are going to be shaded from the ambient light.

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  20. My son's friend done this and is trying to get him to do it he came home to tell me about it and wants to do it he's only 10 what can you compare the shock to and on a scale of 1to 10 how was the pain does it burn the skin I told him no but as a dumb parent lol have become so curious about it I wanted to try it myself haha. I stuck my doing a on a large battery like 12 volt and is it a shock like that or like a wire. Or like a new sting

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    1. It’s not really a shock, it’s burning. Did it to myself and wound up with a tiny burn wound in that spot I was doing it on. You could do it on a ten year old. As long as you don’t keep pressing the button to take a picture a bunch of times, he won’t end up with a burn wound or anything (I did it quite a few times to test if the shock would increase over multiple times, which it did, and which is why it burned my skin). The shock/burn is barely anything, it wouldn’t even compare to the shock you feel from an exposed wire or 12 volt battery, it’s nothing near that. You may need to do it 2 or 3 times in a row though since you the first time you take the picture, you don’t feel anything, it takes a couple times to actually feel it.

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  21. Different phones seem to change the amount of pain you get from it too. I hear iPhones hurt the worst.

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    1. lgs that overheat already hurt the worst

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  22. I am black, african, like blacker than Wesly Snipes black, and i got shocked....

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    1. The same thing had happened to me when I was sipmly taking a photo against my skin. I was shocked and I was very surpised. Maybe it works without sharpie when you have a darker complexion.

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  23. Black sharpie with a Google Pixel yelds no result. Haven't tried it with just the light remaining on yet.

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  24. Ive tried it with a sharpie it works,i tried it with bare skin it did not work, i then tried it on a 12 year old slightly faded black tattoo and it worked it got me good so im inclined to think that it is not chemical feel free to to email me your thoughts at Anthonypope369@yahoo.com

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