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Making Plasma in the Microwave

Short answer: Plasma is gas in which enough atoms have lost electrons that it conducts electricity and glows. In a microwave oven, plasma usually starts where the field gets concentrated: at sharp metal edges, or in the gap between two grape halves.

A 2019 study in PNAS showed the grape effect comes from the fruit acting as a resonator; water-rich spheres trap the microwaves and build a hotspot where they touch, which ionizes the surrounding air. A match flame can do the same by supplying already-ionized gas. Once started, the plasma absorbs microwave energy, rises as a glowing ball and can damage the oven, so I'd treat it as a demonstration, not a kitchen trick. The footage shows a bright, flickering plasma ball inside an inverted glass in a microwave.

VideoWrite-up2 sources

In collections:Everyday Physics

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What should you know about Making Plasma in the Microwave?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Plasma is ionized gas that conducts and glows.

    DD-287-F01 · Write-up · Exhibit A (Ionized gas)

  2. Grape halves can concentrate microwaves enough to spark plasma.

    DD-287-F02 · Write-up · Exhibit B (Concentrated fields)

Video transcript: Making Plasma in the Microwave: A Glowing Ball of Plasma Can Appear Inside a Kitchen Microwave

DID YOU KNOW? Plasma in microwaves is typically created by exciting gases into an ionized state. This can happen when a microwave oven's electromagnetic waves interact with metal objects or thin air pockets causing a strong electric field. This field can strip electrons from the atoms of gases present such as oxygen or nitrogen, ionizing them and creating plasma. The process often starts with a small spark which can ionize more gas molecules leading to a chain reaction. This ionized gas emits light which is why plasma in a microwave often appears as a glowing ball or arc. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 28.7s Reel ·

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The write-up

A glowing ball of plasma can appear inside a kitchen microwave. In 2019, researchers traced grape plasma to microwaves trapped inside the fruit.

  1. Exhibit A

    Ionized gas

    Plasma is gas with enough free electrons to conduct electricity and glow.

  2. Exhibit B

    Concentrated fields

    In a microwave, plasma usually starts at sharp metal edges or between grape halves.

  3. Exhibit C

    Grapes as resonators

    A 2019 study found grapes trap microwaves and build a hotspot where they touch.

  4. Exhibit D

    A glowing ball

    Once started, the plasma absorbs microwave energy and glows as a ball.

  5. Exhibit E

    Hard on ovens

    Microwave plasma can damage the oven, so it's a demonstration, not a kitchen trick.

Questions people ask about Making Plasma in the Microwave

What is plasma?

Free electrons make it conduct and glow.

Source: Write-up · Exhibit A (Ionized gas) · Wikipedia: Plasma (physics)

Where does microwave plasma usually start?

Those spots concentrate the field.

Source: Write-up · Exhibit B (Concentrated fields) · Khattak et al., PNAS (2019): Linking plasma formation in grapes to microwave resonances of aqueous dimers

What did the 2019 study find about grapes?

The hotspot forms where they touch.

Source: Write-up · Exhibit C (Grapes as resonators) · Khattak et al., PNAS (2019): Linking plasma formation in grapes to microwave resonances of aqueous dimers

What does the plasma do once started?

It often rises to the top of the cavity.

Source: Write-up · Exhibit D (A glowing ball) · Wikipedia: Plasma (physics); Khattak et al., PNAS (2019): Linking plasma formation in grapes to microwave resonances of aqueous dimers

Why not try it at home?

The plasma can scorch the cavity.

Source: Write-up · Exhibit E (Hard on ovens) · Khattak et al., PNAS (2019): Linking plasma formation in grapes to microwave resonances of aqueous dimers

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. What is plasma?

    1. Ionized gas
    2. Superheated water
    3. A type of metal
    4. Liquid light
    Show the answer

    Answer: A. Ionized gas Free electrons make it conduct and glow. Source: Write-up · Exhibit A (Ionized gas) · Wikipedia: Plasma (physics)

  2. Where does microwave plasma usually start?

    1. At sharp metal edges or between grape halves
    2. In the oven's fan
    3. In the door glass
    4. Anywhere at random
    Show the answer

    Answer: A. At sharp metal edges or between grape halves Those spots concentrate the field. Source: Write-up · Exhibit B (Concentrated fields) · Khattak et al., PNAS (2019): Linking plasma formation in grapes to microwave resonances of aqueous dimers

  3. What did the 2019 study find about grapes?

    1. They act as microwave resonators
    2. They contain metal
    3. They emit radiation
    4. They block microwaves
    Show the answer

    Answer: A. They act as microwave resonators The hotspot forms where they touch. Source: Write-up · Exhibit C (Grapes as resonators) · Khattak et al., PNAS (2019): Linking plasma formation in grapes to microwave resonances of aqueous dimers

  4. What does the plasma do once started?

    1. Absorbs energy and glows as a ball
    2. Cools the oven
    3. Disappears instantly
    4. Turns into liquid
    Show the answer

    Answer: A. Absorbs energy and glows as a ball It often rises to the top of the cavity. Source: Write-up · Exhibit D (A glowing ball) · Wikipedia: Plasma (physics); Khattak et al., PNAS (2019): Linking plasma formation in grapes to microwave resonances of aqueous dimers

  5. Why not try it at home?

    1. It can damage the oven
    2. It's illegal
    3. It needs special grapes
    4. It only works in labs
    Show the answer

    Answer: A. It can damage the oven The plasma can scorch the cavity. Source: Write-up · Exhibit E (Hard on ovens) · Khattak et al., PNAS (2019): Linking plasma formation in grapes to microwave resonances of aqueous dimers

Cite this case file

Easterling, Marcus. "Making Plasma in the Microwave." The Detail Department (DetailEnjoyer), case file DD-287, last updated Aug 2, 2024. https://detailenjoyer.com/case/making-plasma-in-the-microwave/

Permalink: https://detailenjoyer.com/case/making-plasma-in-the-microwave/ · Last updated

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Cite a single fact by its ID, for example DD-287-F01 → https://detailenjoyer.com/case/making-plasma-in-the-microwave/#DD-287-F01

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