Microwaving Grapes… to Create Plasma?

By Xavier Lam

For the past two decades, scientists could not explain the phenomenon of a grape being microwaved, and creating a flashy spark of hot ionized gas (plasma). However, scientists from Canada have recently been able to figure out why grapes ignite in this way. Their study observes that the microwaves are actually creating “hotspots” of electromagnetism.

grape creating plasma (c) Hamza Khattak/Trent University CC BY-SA 3.0

Pablo Bianucci, an associate professor in the Department of Physics at Concordia University in Montreal, with his co-workers, tested the phenomenon on grapes, hydrogel beads, and water-filled quail eggs. Using a combination of thermal-imaging, computer simulations, and a household microwave, the scientists were able to come up with an explanation for what they were seeing.

The size of a single wavelength of microwave radiation coincides with the composition (mostly water) and size of a grape. Therefore, grapes can fit microwaves entirely inside them and can “trap” them. When the microwaves become trapped in the tissues of each grape half, they use the connecting skin as a bridge, “hopping” from one grape hemisphere to the other, Bianucci explains.

grape thermal imaging (c) Hamza Khattak/Trent University CC BY-SA 3.0

“This results in a ‘hotspot’ with a much stronger electromagnetic field in between the grapes,” he said. “It is this strongly amplified field that results in the generation of the plasma.”

While creating plasma with grapes is a fun trick, it also has some real applications. The phenomenon focuses electromagnetic energy from a wavelength of around 12 cm to a tiny spot of a millimetre. By using light instead of microwaves, you could focus the energy to an even smaller spot of a couple nanometers. This would aid in the building of computer chips that are even smaller than our current ones.

I find this topic interesting because it had been something of an unsolved mystery until now. I was also surprised of its applications, as it could possibly lead to smaller computer chips as well as the continuation of Moore’s Law. If you want to know more about the microwaving of grapes, I suggest watching this great YouTube video by Veritasium.

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