Kernel of truth

Yesterday I received a link — buried at the end of a long chain of e-mail forwards all saying variants of, “Wow, this is scary!” — to a video that depicted groups of people using stray microwaves from their cell phones to cause popcorn kernels to pop.

In the video, three or four phones are placed on a table in a ring around a few popcorn kernels, and then someone dials each of the phones to cause them to ring. Within a couple of seconds the kernels start to pop.

The sender who forwarded it to me asked if I knew whether this was for real.

My reply asked the sender to consider the power available to a cell phone versus the power available to a microwave oven. A microwave oven draws 15 amps of current from the household mains, producing hundreds of watts of focused microwave energy with the specific purpose of heating up food placed in the target area — and even so, it takes at least 30 seconds of exposure for the first kernel to pop. A cell phone, by contrast, houses a battery rated in milliamp-hours, with a typical one holding 1500 milliamp-hours of energy. This means it can draw 1 milliamp for 1500 hours, or 1500 milliamps (1.5 amps) for one hour, and so on. If a cell phone tried to draw 15 amps from such a battery, then (apart from the phone melting) the battery would be depleted in 1/10 of an hour — six minutes. Clearly cell phones do not draw 15 amps, but even if they did, they wouldn’t convert nearly as much of that energy into microwaves as microwave ovens do; and even if they did that, the microwave energy wouldn’t be focused the way it is in a microwave oven. Yet the video depicts the first kernel popping within about three seconds.

If that much microwave energy really were reaching the popcorn kernels, we’d also be seeing the other effects of powerful microwaves on objects in the immediate vicinity. For example, we’d see sparks and electrical arcing from metal objects, including the cell phones themselves. But we don’t.

Finally, why would a ringing cell phone cause popcorn to pop? To ring, a cell phone merely has to receive an “incoming-call” signal from a cell tower. The phone doesn’t begin transmitting any appreciable amount of power until after you answer it and begin speaking!

At this writing, the video in question has a supposed 11,031,929 views. When I think of all the people across the Internet who are now arranging their cell phones in rings around a handful of popcorn kernels, I despair.