Why Your Fork Sparks In the Microwave

Listen while you read: Late Of the Pier - Focker

This is a topic that brings a lot of excitement to me because I have for several years studied RF theory and electronics. I'm writing this post because I believe there are many common misconceptions with RF even though most of our society is so dependent on it.

So, the question is: why does metal spark inside your microwave? The same way sunlight passes through windows, microwaves also pass through some materials. Materials like glass, paper and plastic are unaffected by microwaves. Metal however, reflects microwaves. Yes reflects, just like a ball bounces off a wall. The metal walls of a cooking space actually work like a resonator containing all the waves inside the space. So why then does tin foil or aluminum spark and catch on fire when I nuke leftovers in the microwave and not this metal surrounding the microwave? Something called frequency resonance.

Have you ever heard a wine glass vibrate when you play the right piano key? The wine glass vibrates because its body is tuned to the right frequency. When the sound waves from the piano hit the glass they are vibrating at the right frequency to make the wine glass in turn vibrate to the same frequency.

Now, microwaves are electromagnetic waves, which are oscillating electric and magnetic fields. The oscillating waves cause current to run through metals and other conductors, the build up of current causes the metals to heat up. This is the reason thin metals from a microwaveable pizza meal heat up. The reason some metals spark or even catch fire in a microwave is because current can build up so tremendously at the sharp points of metals. The electrical potential can be so great that the air around can conduct electricity, causing an arc between two conductors.

How does the metal surrounding the microwave not heat up? Again, frequency resonance. The surrounding metal is tuned to the exact frequency of the microwave. The metal and microwaves produce a uniform electromagnetic wave pattern, in which there is no current buildup thus no heat. Oddly enough, the frequency of the microwave is the same frequency of your cell phone, 2.45 GHz. So when talking on your phone you are essentially cooking your brain with a very tiny microwave. This is why some people have headaches while talking on the phone all day, putting on a tinfoil hat is going to make things worse by the way.

Thanks for all the responses from Twitter. You can follow me if your not already just look for kurf.

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healthfreak said...

Nice articles on electronics circuits...i thinks this is really good stuff for engg student..will refer it to my juniors who are still in college....well i see the look and feel of the blog has changed as well and now its looks awesome!!!...nice work man...

Kurf said...

Thanks, healthfreak, tell them this is a live thing, There's Ustream and a chat client. So I welcome questions. Thanks for taking a second look.

Anonymous said...

Thanks, you helped me with my report!