Biology teacher says don't open microwave till beeps stop because microwaves still bouncing around

This was just told to me by a college aged co-worker as I reached into the microwave to get my oatmeal after it powered down but was still beeping the 4 or so “it’s done” beeps. I told him that was insane and his HS biology teacher was an idiot.

He said “Prove me wrong!”

I don’t even know here to start with this nonsense. Microwaves don’t “linger” once the oven’s magnetron shuts off.

I’ve met many people who even open the microwave while it’s still heating food and hasn’t completed the full time. For some reason, that always seemed a bit dangerous to me. I press the stop button first and then open it. But I don’t wait the time equivalent to the 4 beeps at the end.

Well, microwaves do kinda bounce around after the magnetron shuts off, they just bounce at the speed of light and so have finished bouncing by the time the brain has registered that the timer has dinged. Also, even if some microwaves somehow escape through the open door, who cares? They’re low energy and are harmless unless you’re getting bombarded with enough of them to actually cook your flesh.

The only chance of microwave leakage is the time lapse between unsealing the edges of the door and the cut-off switch turning off the magnetron.


And also, just a few watts of RF energy. You probably get as much holding a cell phone to your head while talking.

Color me not the slightest bit concerned.

Yes, and if you turn off the light and you’re quick enough, you can be in bed before it gets dark, while the light is still bounding around the bedroom.

The most instructive message from this biology professor was the difficulty of proving a negative, or an absurdity to be false.

There you go. Succinct, to the point and correct. Also mention that his HS Biology teacher is an idiot.

Microwaves don’t “bounce around” when it is off but it wouldn’t even matter if they did. Microwave radiation isn’t like nuclear radiation. All it can do, even if you rig up a microwave to stay on when you open the door, is make you warm if you stand too close to it. That is how inventors first came up with the idea for using it to heat food in the first place.

Perhaps the proof you seek can be found using a Geiger counter … see, no readings.

Hope the gravity waves don’t hurt the bio-teacher when the microwaves bouncing around knock it off the counter.

Tell him that you don’t have to “Prove him wrong!”, then put the point across by making a half dozen wrong but unverifiable statements and saying “Prove me wrong!”.

Microwaves travel much faster than sound, so if the buzzer sounds simultaneously with the magnetron being shut off, you can’t hear the buzzer before all the echoed waves have been absorbed by your food.

Show them this video.

If you put a CD in a microwave, it will completely destroy the CD, but will make a pretty light show while doing so. So you can tell from the arcing exactly when the radio waves stop bouncing around inside the box. You'll note from the video that the arcing stops at the same time as when the timer hits END, and the beeps don't even start until a fraction of a second after that.

Microwaves don’t keep bouncing around any more than light waves continue to bounce around a room when you turn off a light switch.

However, there can be a danger of escaping microwaves if you pop the door open while it’s running. There’s an interlock of some sort that switches off the microwave when you open the door, but it’s a mechanical switch. There’s always the chance that the switch doesn’t work or there’s some delay between when it senses the door is open and it flicks off the microwave. In most cases it works fine, but there’s always the chance that the switch sticks in the wrong position and doesn’t shut off the microwave. To be safest, turn off the microwave first.

This was a comment by a Biology Teacher… I am with Dr Sheldon Cooper on this:

"Oh, I see why you’re confused. No, her news sounded important, but what you’re forgetting is it was an achievement in the field of biology. That’s all about yucky, squishy things."

OMG, microwave towers, radars, cosmic microwaves. We’re being bombarded by the little things. Tell him this and scare the crap out of him.

Sarcasm: The last thing you want is a stray microwave bouncing off your hand and raising its temperature by .00001 degrees.

I mean, the sun is killing people (thanks, skin cancer), but it’s not like you need to avoid all light from the sun and live like a vampire.

You don’t need to be microwave vampire. Even if a stray wave was possible… I think you’ll go unharmed.

(How I would be in school with said teacher: I’d be yanking the door open as soon as possible in deference to teacher)

This does remind me about an invention… well, more of a hack or project than an invention, which is something you put in a microwave as evidence that it is working. Isn’t that just a cup of water? Heat it and check it? Yes, that works, but you can’t look in and see an indication that the magnetron is on. Say that like me, you like to fiddle with the power setting because you believe (with poor justification ?) that certain foods should be reheated more slowly. Does the change in the sound of the microwave mean the magnetron is off, or has gone to lower power, or is it just the fan, or what?

So why not make a little antenna connected to some led’s that shows the current microwave flux ? Throw it in with your burrito and watch the light show. Be the first one in the household to know for certain, yes, that loud bang means something happened to the power supply of the magnetron.

And of course, convince biology teachers that it is safe now to open the door.

Let’s say the microwave malfunctions. The door flies open as the soup you were cooking explodes, and it’s still going.

What’s the best course of action? Is it safe to go up to it and turn it off. Do you stay away (how far away?) until the timer runs out? Is there any danger of nearby objects catching fire?

You’ve just been hit by flying glass, metal and hot soup, and you’re worried about some stray microwaves?

Only one of those things lets the government hear my thoughts!

:: puts tin-foil hat on ::