Why does microwaving grapes make plasma

The key, it seems, is cramming the energy present in microwaves into a very tiny space—the point of contact between the objects in question. In your garden-variety microwave oven, microwaves have a wavelength of about But adjoining grapes which are full of water that can absorb said microwaves can concentrate the energy within into a region where the two spheres touch, which is no more than a couple millimeters wide. This creates a very strong, very condensed electric field at their interface—a pocket of ammo powerful enough to liberate negatively-charged electrons from, say, the salts naturally present in grapes and other fruits.

And the results are explosive. In these cases, the energy simply concentrates at the center of the grape. With microwaves of this wavelength, typical grapes have a pretty ideal diameter. Conversely, undershooting the size will prevent the spheres from absorbing enough energy to begin with. All these theories that were developed with pencil and paper can actually be applied to something you throw into your microwave.

Receive emails about upcoming NOVA programs and related content, as well as featured reporting about current events through a science lens. And beyond piecing together the physics behind parlor tricks, the results could have implications for broader studies on plasma and light, says Julie Biteen , a biophysicist and chemist at the University of Michigan who was not involved in the study. So do waterlogged beads called hydrogels, tests show. Researchers in Canada found that the grapes act as resonators for the microwave radiation.

That means the grapes trap this energy. For a time, the microwaves will bounce back and forth inside the grape. Then the energy breaks out in a flash. But if two grapes sit next to each other, that hot spot forms where the grapes touch. Salts within the grape skin now become electrically charged, or ionized. Releasing the salt ions produces a plasma flare. The researchers used household microwaves with disabled turntables, operating at 2. Results showed that a microwaved grape's size and composition — particularly the amount of water it contains — determine the fruit's ability to light up, Bianucci told Live Science in an email.

Here's why: Size and water content affect how grapes — or other small spheres, such as beads, berries, grape tomatoes or olives — interact with microwave radiation, Bianucci explained. When two connected halves of a grape are bombarded with radiation , microwaves that become trapped in the tissues of each half can use the connecting skin as a bridge, "hopping" from one grape hemisphere to the other, according to Bianucci.

Prior to the researchers' experiments, it was widely thought that microwaved grapes produced plasma through surface conductivity, with the ion-rich flap of skin connecting the grape halves transmitting an electrical current that generated the plasma. While this was a plausible explanation, it had never been verified in a peer-reviewed study, and that prompted study co-author Aaron Slepkov, an associate professor in the Department of Physics and Astronomy at Trent University in Ontario, Canada, to put grapes into microwaves for science.