(This means you will need to switch the plasma globe on and let it run for a few minutes before starting each experiment.) Plasma globes should be able to run for an entire lesson without overheating, but if you notice that your plasma globe overheats after constant use, we recommend that you switch it off between one experiment and the next, or every 30 minutes.For the same reason, never cover the globe when it is on or still hot.If the paper is then touched using another metallic object, such as another coin or a paper clip, a hole will be burned in the paper. A possible experiment, if conducted with care, is to place a coin on top of the globe and then place a piece of paper on top of the coin. Avoid touching the globe with metal objects that will rapidly heat up and can cause burns.Plasma globes are high-voltage electrical devices, so when using them, always ensure all safety measures needed when working with electric currents are in place. (The reason is that a hand placed near to the globe helps it to discharge, because the human body is a better conductor than the air and so provides an easier escape route for the electrical energy from the globe.) You can challenge them to explain why almost all streamers combine into one, which is attracted towards a hand and will follow it. In this first experiment, students bring their hands close to the globe and see what effect this has. Plasma globes can provide this experience and reveal some of the properties of plasma – for example, its ability to conduct electricity. Although it is the most abundant form of ordinary matter in the Universe (accounting for more than 99%), plasma is never usually encountered in normal life. In physics, plasma is referred to as the fourth state of matter (after solid, liquid and gas) w1. This sets up an associated electromagnetic field in the same region, although the intensity of these fields diminishes with increasing distance from the coil. The electrode at the centre of a plasma globe is a device called a Tesla coil, which creates an alternating electric field that reaches beyond the globe itself and into the surrounding space. With no single best path for the electrical discharge to take from the centre of the globe, the streamers constantly move and flip around – like lightning finding a path to Earth. But unlike a neon light, in which the electrical discharge passes directly between two electrodes, a plasma globe has only one electrode at its centre. The plasma transmits current easily because of its ionised state, and this produces the glowing streamers we see – just as the gas in a fluorescent tube or neon light glows when it is switched on. When the globe is switched on, the electrode produces a high-voltage current that alternates at high frequency, which heats the gas to a high temperature and splits the atoms into ions – forming a state of matter called plasma. Inside the sphere is a central electrode and some inert gas. What are plasma globes?Ī plasma globe (or plasma ball) consists of a thick glass sphere on a base with an electrical connection. But are these striking luminous orbs anything more than just a novelty table-top toy? This article aims to show that there is plenty of interesting physics to demonstrate – entertainingly – using these intriguing devices. With their glowing pink flares and threads of purple lightning, plasma globes are fascinating to watch. Plasma is the fourth state of matter, after solid, liquid and gas – but what is it like and what can it do? Plasma globes allow us to answer these questions – and more.
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