Grape fizz: The skinny on microwaving

Q. Why do grapes spark in the microwave? –Bacchus

 A. Don't try this, unless your life insurance is paid up and you have a spare microwave in the basement! This one comes from the Mad Scientist Network (, posted by microwave physicist Adrian Popa. Not all microwave ovens give the same results, but Popa cooked grapes set atop an inverted centered water glass, using large fresh red grapes (1" diameter) with stems removed, and limiting the timer to 10 seconds.

Solo grapes ejected steam out of the stem hole, propelling them like little rockets. Without the stems removed, grapes would simply "rupture in a small explosion" (why you should never cook eggs in the shell).

When two de-stemmed grapes were set close together, hole to hole, the arcing and sparking began, along with a 120 Hertz buzz following the pulsing power of the microwave magnetron tube. The two jets of steam, excited into a plasma state, formed a conductor. With the grapes one millimeter apart, a 3000-volt potential between them created the arcing. "This is a considerable amount of voltage."

Another caution: Never turn on a microwave without something inside. Heating a few grapes could also zap the oven, if the water in the grapes evaporates too quickly. So please don't try this! (We sure didn't.)

Q. Are zoo animals happy in captivity? ­Ling Ling

 A. Why shouldn't they be? Most live longer than their counterparts in the wild, eating better and safe from predators. Zoos have come a long way since their start as private menageries, displaying exotic and dangerous creatures for the amusement of the nobility, says West Chester University psychologist Michael J. Renner.

Nowadays education and conservation are the watchwords. Several species exist only in zoos, or became extinct in the wild, then were reintroduced there from zoo stock.

For most species, there are recognized behavioral signs if an individual isn't doing well (i.e., is "unhappy"), such as excessive inactivity or repetitive behaviors like pacing. Agencies that accredit zoos now require them to mind animals' mental health, and many zoos actually employ "behavioral enrichment" specialists. Ideally, a zoo environment permits natural patterns, such as a leopard chasing prey, an ape climbing, a gazelle galloping.

"Treated thus, zoo animals can be persuasive inter- species ambassadors, encouraging us human visitors to become better stewards of the Earth," Renner says.

Q. At Logic Inc., management promises a "surprise" fire drill in the coming week, Monday through Friday, to test the efficacy of evacuation procedures. No one but the CEO knows which day it will be. Can you guess when the alarm will most likely ring? ­J. Taliaferro

A. You might say each day is equally likely at one chance out of five. But for a shrewder approach, try a "reductio" argument: Assume a Friday drill is planned. The problem here is that once Thursday passes and still no drill, there would hardly be any surprise to Friday. So Friday can't be the day.

And then Thursday can't be it either, because if Friday can't be the day, then once Monday-Wednesday have passed, Thursday would have to be the day, and so no surprise. Therefore rule out Thursday. See what's coming next? For similar reasons, Wednesday can't be the drill day, nor can Tuesday or Monday.

Likely conclusion: Management, wise in the ways of logic, is pulling a fast one. It wants the staff to report back that such surprise fire drills are not possible, that this must be an "Are you on your toes?" test.

So, were you on your toes?

Send Strange questions to brothers Bill and Rich at