Weird Science Tricks


Everybody’s favorite — microwaving a lightbulb.  Pretty!

At least two posts suggest that if you put the bulb in a mug of water (with the bulb part sticking up) then it won’t explode.  I believe that’s because the water acts as a dump for the microwave energy, keeping the bulb from heating up out of control.

What’s going on?  This is similar physics to two of my previous posts (microwaving a CD, and the microwaving a grape post).  Lightbulbs are a partial vacuum inside, but also have a small amount of gas, usually Argon.  The microwave makes a current in the metal of the bulb (just because microwaves push charges around).  This current lights up the filament in the light bulb.  But it doesn’t glow in the way that you’re used to seeing a lightbulb glow because the high voltage creates a plasma inside the lightbulb (remember, this is an ionized gas), and the gas glows purple.  I’m pretty sure that this doesn’t require the lightbulb filament — in other words, this should work with a burned out bulb.

The light pulses because the magneton that creates the microwaves in your microwave oven is pulsing on and off.  I’m not quite certain why there are the different colors created, though it seems to be related somewhat to the rotation of the bulb in the microwave.  It may simply be that at different angles, the lightbulb acts as a stronger or weaker antenna for the microwaves, creating more or less voltage, and thus a plasma that glows at different colors as more or less energy is dumped into it.

I never found a good comprehensive site with a succinct explanation, but this page has some interesting discussion.

This is actually what normally happens in a regular fluorescent tube light (that is, an ionized gas glows), so if you put a fluorescent tube light in the microwave, it should glow like normal.

A friend pointed me to this wonderful set of videos, “Is it a good idea to microwave this?”

His favorite, he says, is the giant mercury lightbulb.

OK, I wouldn’t let it run quite as long as these bored college students did, but it DOES look REALLY cool (and it’s a great use of those annoying AOL CD’s, or the romantic mixes that your old boyfriend made for you):

And another really pretty one (gotta love the Darth Vader-esque breathing in the background), with an extra bonus:  aluminum foil!

You can play around to see if it matters if there are images on the CD, if it looks different printed side up or shiny side up, etc.  This site claims that it works best label-side up, and that the less ink on them, the less they smoke.

As you know, it’s not supposed to be good to microwave metal.  That’s because the microwaves can push the electrons around in the metal.  (Electrons in non-metal, or non-conductive material are kind of glued in place, so they can’t be pushed around).  That can make the metal heat up (just like a metal wire will heat up when it’s conducting a current) and do all sorts of bad things to your microwave.  You can read more about microwaves and what they do to metals here.

So, CD-ROM’s have a thin aluminum layer.  And the microwaves push the electrons around in the aluminum, making big currents, which heat up the aluminum so much that it vaporizes (turns into steam)!  The electric current is still there, though, so it jumps across the vaporized aluminum (making a pretty light show) to get to another section of aluminum.  There is a little bit of similar science between this and the Microwave a Grape activity I posted earlier, in that you’re seeing air glow as electrons jump through it (a phenomenon called arcing).  You’ll see a bunch of little paths burned into the aluminum after a while.   An interesting observation from this site:

Some of the islands will be shaped so that they make very good microwave antennas. These spots will focus the microwave energy, and get very hot. Now you will see just a few bright spots spewing a lot of smoke. The good part of the light show is over, turn off the oven.

Here is a lovely image of a CD post-microwave, showing beautiful fractal trees where the electrical arc made its way across the aluminum.

800px-microwaved_disks-cover_fractal_trees_ceb400491

I’m still a little confused as to why the patterns burned in the CD follow these circumferential patterns.  I imagine that the CD data is originally etched in circumferential patterns, making the aluminum thinner in these regions, and thus channeling the electricity in these circles.

For extra fun, if you happen to have a Tesla Coil lying around, here is what happens when you place the microwaved CD on top of the Tesla coil.  I got this from ElectricStuff.co.uk, which has even more pictures.

cd3

I believe what’s happening is that the electric current from the Tesla is flowing just through the parts of the CD that still have aluminum on it, generating high heat and arcing in lovely patterns.

I’m surprised at the number of people who haven’t seen this one, but then again, neither had I until I went to the Exploratorium (where they’ll stick anything in a microwave).

Put a bar of Ivory Soap (no substitutes!) on a paper towel in the middle of the microwave.  Press go.  About 2 minutes should do it.  Here’s what happens:

And this video will show you what it looks like when you take it out afterwards

What’s going on?  Well, the reason that Ivory Soap floats (try it) is that it’s puffed full of air (here’s some history of why that is).  There are tons of tiny bubbles whipped into it, sort of like when you make whipped cream.  It’s an emulsion of soap and air.  The bubbles of air have water vapor in it.  When you microwave it, that water vapor creates pressure on the air bubbles making them expand and puff up.  The air bubbles themselves expand as they heat since the volume of a gas increases with temperature (Charles’ Law).  And the soap softens, which allows the whole thing to expand into a big puffy pile.  And when you stop heating it?  The soap’s no longer soft, so it gets rigid and hard, but stays its expanded puffy self.  You can use it like soap now, though it’ll be a little weird!

Other brands of soap tend to just melt.

Here’s a nice explanation, as well as how to use this as a classroom lesson on density, from Steve Spangler Science.  And some more classroom suggestions from About.com.

Hey, this blog has moved! Click here to see this post.

Here’s what you do — slice a grape in half, but keep the halves connected by a little “hinge” of grape skin.  Some suggest drying off the grape halves a little.  Some suggest using a green grape in particular, and some say to cut it in quarters. Put the two halves next to each other, face up, in the microwave.  It’s best to place it slightly off-center, as microwaves have hot-spots and “nodes” and the center is a “node” of radiation.  Press go.  Click here to read the rest….

I’ve been wanting to do a series of posts on Fun Things To Do with a Microwave, and I’m just going to get off my butt and DO it!   For some of these to work well, you need to know where your microwave hot spots are.

What do we mean by hot spots?  Microwaves are just one form of radiation — like x-rays or visible light — of a particular frequency.  The reason they chose microwave frequencies for ovens is that this frequency is more readily absorbed by water.  The microwaves are pretty long (about the size of a grape, as you’ll see in the next post), so you get a regular pattern of peaks and troughs (or hot and cold) as the waves add and subtract  (it’s a checkerboard, like two-slit interference).  You may have noticed that food cooks slower at the center of a microwave and faster at certain other places (that’s why those rotating plates are handy).

Method 1:  THE WATER METHOD  (From RealSimple)

You can find the hottest parts of your microwave by placing custard cups or small bowls filled with water all around the oven. Heat for 1 to 2 minutes, checking every 30 seconds. The ones that boil first are in the hot spots.

Method 2: FAX PAPER gives a more permanent map (from Barnesos.com)

Take a damp paper towel and place it on top of 5-10 other paper towels in the bottom of your microwave. On top of it, place a sheet of themally sensitive fax paper, the kind that old crappy fax machines use. Credit card recipts also work, but they’d be harder to tile the bottom of your microwave with. The extra towels at the bottom provide some insulation. Turn the microwave on for a while. The first areas on the paper to turn dark are the hot spots.

Method 3: MARSHMALLOWS (or chocolate chips)

Or a tasty way is to place marshmallows all over the bottom of the oven (might want to put a paper towel down first).  Greater pixel resolution with the tiny marshmallows (more Marshmallows Per Inch!)

Here’s a kid-friendly explanation of microwaves (as well as a simulation of the marshmallow method) and a kid-friendly explanation of hot spots.

A few cool things about science that relate to the holidays.  I wrote this *before* Christmas, but, oh well, better late than never?

Dot Physics has a wonderful post on why Christmas tree lights stay lit even when one of them burns out, which is an unusual way for a series circuit to work.  Some nice explanations using Kirchoff’s laws make this a wonderful little post to stimulate a science lesson for the season.

From Sebastien Martin

From Sebastien Martin

I have an old post on why it’s a myth that no two snowflakes are the same shape.

And Morning Coffee Physics has a delightful little post on why snow sparkles. This is just my kind of science — gorgeously explanatory post about something we see every day.

Sebastien Martin at the Exploratorium has some beautiful images on his Flickr site showing how they used Christmas lights to demonstrate resonance and harmonics (see picture at right).

Steve Spangler Science gives you some ideas to deck the halls…holiday decorations with science.

And then of course there’s the old favorite Instant Snow (video on Teacher Tube).  Insta-Snow is made from sodium polyacrylate, a water-absorbing polymer.

And on the Ellen show….

Here are some great gems from some really old posts over at Swans on Tea. Thanks to Rhett at DotPhysics for the technical assistance.

Robots doing amazing things:

Carbon dioxide is heavier than air (neat thing to try at home)

Weird psychology trick (how does he do that?)

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