Tag Archives: Plasma

Microwave Plasma

We go through our daily lives encountering three of the states of matter; solid, liquid, and gas; nearly every moment, but the fourth, plasma, is much rarer for most of us. Plasma can be found around most forms of visible electricity, like lightning, but you can find it inside your microwave if you follow the steps below. Before you get started, however, this experiment MUST be carried out with immense care and with an adult present; it is very easy to get this experiment wrong and deal damage to not only your microwave, but yourself as well.

For this experiment, you’ll need a microwave, a toothpick, a microwave-safe glass container, three discs of cork (or any material you can stick a toothpick into and use to prop up the glass, and a match. Place the four discs of cork in the microwave so that one is in the center and the other three are around it far enough for the glass container can rest on top of them. This is essential, as air needs to flow between the inside of the glass container and the inside of the microwave. Stick the toothpick into the center cork disc, and set the microwave to 20 seconds, but don’t run it yet.

microwave plasma

Light the toothpick and cover with the glass container, closing the door of the microwave and hitting start. You should see arcs of plasma coming from the lit toothpick and while it’s tempting to leave it go and watch for a while, only let it run for a few seconds. Otherwise, the glass will get too hot and could shatter, spreading broken glass through your microwave and removing the housing for the plasma, potentially lighting your microwave on fire. After you’ve shut off your microwave, let it sit closed for about a minute, allowing the glass to cool down, otherwise the sudden inrush of cool air from the outside could shatter the still hot glass.

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Those plasma arcs were cool, but how exactly did we make them? Well, plasma is essentially ionized gas, requiring either an increase in heat or adding more electromagnetic force, both of which are happening inside the microwave. When an object is burned, the fire is actually stripping away electrons, ionizing the atoms around the fire until the electrons get recaptured. Microwaves work by establishing a standing wave of electromagnetic fields, which push and pull the electrons stripped away from the fire. This causes them to collide with the air molecules inside the glass, adding heat to the air and stripping away more electrons. This continues until the air is ionized to the point of becoming plasma, dissipating, and then ionizing into plasma again. The reason we can actually see the plasma also comes down to those electrons, as their collisions with the air molecules can add energy to the air’s electrons, which then fall back into their normal energy levels and release light, similar to the effect of fluorescence we’ve mentioned in previous pieces.

If you want to make plasma yourself, get an adult and try it, but please remember to be careful.

What’s the Matter: Is Fire a Plasma?

Is fire a plasma? Turns out it’s not a trivial question! The answer depends on how you define the parameters of the fourth state of matter. Descriptions of plasma commonly include the following points: plasma is what happens when a gas is subjected to lots of ionizing energy. Although thoroughly ionized, it is quasi-neutral. Its molecules display collective dynamics and respond as a group to electromagnetic influence.

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The sun as seen by NASA’s IRIS orbiter. Ultraviolet image translated into false color for human consumption. Stars, including our sun, are made of plasma.

Most of the observable universe is made up of plasma! Astrophysical plasmas are mind-blowingly hot. On Earth, too, plasma is created by copiously applying heat or otherwise energizing a gas, although plasmas can also be created in laboratory scenarios that are cold by human standards.

So, which state of matter does fire belong to? Depending on who you ask, a flame is either a low-level plasma or a lightly ionized gas. A flame is a heated volume of air in which some electrons have broken free from their nuclei, but it’s not hot enough (or ionized completely enough) to enable cohesive electrodynamic behavior on the level of, say, an arc welder.

 

Plasma or not, the gas within a flame contains enough ions to make it a decent electrical conductor! Here, electricity arcs from a generator to a candle flame.

Fantastic Plasma

The universe is full of action at a distance. Planets and stars tug on each other via the gravitational force. Magnets attract or repel based on their polar orientation. An object’s area of influence is called its field. Gravity, electricity, and magnetism are some of the most common field interactions.

plasmabulb2

The plasma ball’s central electrode transmits an electromagnetic field that extends far beyond its glass shell. Need proof? Try holding a fluorescent light tube nearby. The field generates electricity by setting electrons in motion, lighting the bulb!

Inside the globe is a miniature atmosphere of noble gases. These are less dense than air and ionize at relatively low voltages. At the core of this noble cloud, a high-frequency oscillating current creates a large buildup of negative charge. Like charges repel each other, so the buildup discharges outward in lightning-like plasma filaments.

PlasmaBall

Plasma is the most abundant state of matter in the cosmos. Solids, liquids, and gases are more familiar on Earth, but in the big picture, plasma is everywhere! It’s what stars are made of, and stars comprise most of the known mass in the universe. So, what is this stuff?

MagneticSunAdding energy to a solid weakens the attachments between its molecules, so it melts into a liquid. Add even more energy, and the molecules detach completely– that’s a gas. Plasma is what happens when a gas becomes so highly energized that electrons actually separate from their respective atoms, creating an electromagnetic fluid.

Bring gravity and rotational dynamics into the mix, and some crazy field patterns emerge. The NASA image at right shows the sun’s magnetic field lines. This behavior is the source of stellar weather like sunspots and solar flares, which have measurable effects on GPS and other systems. Large coronal mass ejection events can even blow out power grid transformers on Earth! Aerospace engineers, pilots, and electrical companies get forecasts from the NOAA Space Weather Prediction Center just like most of us check the weather at home.

Written By: Caela Barry

DIY + Grapes + Microwave = PLASMA!

WARNING: Handle dishes with a potholder, and be aware that they may break if left in the microwave too long. Always keep a fire extinguisher on hand when experimenting with high-energy science. 

What do lightning, the aurora, neon signs, and grapes have in common? Plasma! It might be the least familiar of the four states of matter (solid, liquid, and gas are the other three), but it’s actually the most common form of matter in the universe. It’s what stars are made of!

Plasma1

This 2002 coronal mass ejection (CME) on our sun blasted plasma out into space at millions of kilometers per hour! During periods of high solar activity, it’s not uncommon for scientists to observe 2 or 3 CMEs per day. Image credit: NASA

Plasma is what we get when we apply enough energy to a gas to strip molecules of their electrons. This energy typically comes in the form of heat or a strong electromagnetic field like lightning. If you have access to a microwave, you have a great source of electromagnetic waves to work with! Normal microwave use doesn’t produce plasma, though– it takes an antenna to create a strong, steady field.

A microwave heats food by barraging it with electromagnetic waves, causing the molecules inside to vibrate (see previous post for more in-depth microwave science). In this experiment, we’re interested in the waves themselves. A typical microwave oven radiation wavelength is about 12cm, or just under five inches. A line of four grapes is about five inches long. Thanks to this ratio, a grape makes a great antenna for our DIY plasma project!

Plasma2

Here’s why it works: a half-wave dipole antenna is an antenna made of two matching parts, each about ¼ the length of the wave the antenna is supposed to receive. This style of antenna does its job so well that it’s the standard in radar technology and other fields. You may even have seen it in your living room as “rabbit ears”  on a television! Conveniently, grapes conduct electricity well, and a typical grape diameter is about ¼ the size of a microwave oven wavelength. This makes two grapes next to each other (or one halved grape) an ideal antenna for concentrating the waves inside the oven. The grape antenna creates a strong, uniform electromagnetic field… exactly what we need to strip gas molecules of their electrons. Give the field a little time to gain intensity, and BZZZT! Plasma! DIY style!

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