# How a Plasma Ball Lamp Works How a plasma ball makes, shapes and colours its glowing filaments By gentle\-wombat\-c361f434 Topic: Physics & Chemistry [Open the interactive Jig](https://ask.jig.com/j/HeBKICyaFKUM) ## Transcript ### 1. Lightning in a glass ball? A plasma ball is a glass globe filled with noble gases, mostly neon, at about normal air pressure\. Glowing tendrils, called filaments, reach from a small ball in the centre to the glass; each is a thin channel of plasma, gas whose atoms have been split into free electrons and charged ions\. By the end you will know what makes them, why they glow and why they follow your finger\. Noble gases are the unreactive elements in the last column of the periodic table, such as neon, argon and xenon\. ### 2. Three simple parts A clear glass globe holds the gas\. In the middle sits an electrode, a conductor that delivers electric charge, held up on a stalk\. The black base hides the electronics\. Switch the power off and on to see that the gas itself is invisible until electricity flows\. The globe is not a vacuum: the gas inside is close to atmospheric pressure\. ### 3. High voltage that flips direction Inside the base, an oscillator circuit and a step\-up transformer turn mains electricity into alternating current \(AC\) of about 2 to 5 kilovolts\. Its frequency is about 35 kilohertz: the electrode switches between positive and negative 35,000 times a second, so each cycle lasts only T = 1/f, about 29 microseconds\. Hertz \(Hz\) means cycles per second, so 35 kHz is 35,000 cycles every second\. The flip shown here is slowed right down\. ### 4. An electric field fills the gas An electric field is the region where a charge feels a force; its strength is measured in volts per metre \(V/m\)\. Around a small round electrode the field is strongest close to the ball and weakens roughly as 1/r², where r is the distance from the centre\. Predict what happens to the filaments as you lower the voltage, then try it\. Below a certain field strength the gas stays an insulator \(a material that does not let charge flow\), so no filaments form at all\. ### 5. Ionisation makes plasma A few free electrons are always drifting in the gas\. The strong field accelerates them until they smash into atoms and knock out more electrons, leaving positive ions \(atoms that have lost an electron\) behind\. This is ionisation, and each collision can double the number of free electrons in an electron avalanche\. Free one electron and watch\. Plasma is a gas containing many free electrons and ions, so it conducts electricity\. It is often called the fourth state of matter\. ### 6. Why the filaments glow Collisions also lift atoms into excited states: their electrons jump to higher energy levels\. When they drop back, the atoms give out the extra energy as light, and each gas has its own colours\. Choose a gas mix and predict the colour before you look\. Neon on its own glows a diffuse red\. Adding argon helps narrow filaments form, and a trace of xenon makes the ends bloom\. ### 7. Your finger opens an easier path Glass is an insulator, but your fingertip and the plasma inside, separated by the glass, form a capacitor: two conductors with an insulator between them\. Capacitance is how much charge such a pair can store per volt, and your body has a lot of it, so the alternating current flows into you more easily than into the air\. The filaments gather into one bright channel at your fingertip\. Touch the glass, or press the button\. You do not attract lightning: a tiny high\-frequency current flows through you\. Never touch a plasma ball with metal objects or with hand sanitiser on your skin\. ### 8. Light without wires The rapidly alternating field reaches outside the globe\. Bring a fluorescent tube close and the field drives electrons through the mercury vapour inside it\. The vapour gives out ultraviolet light, which makes the coating glow\. The tube lights only where the field is strong enough, so the end nearest the globe glows most\. Plasma balls can also interfere with nearby touchpads, phones and Wi\-Fi, so keep electronics away\.