How is lightning formed?
Movement of tiny bits of ice and water droplets inside a thunderstorm causes electrical charge to build up in different parts of the cloud. The charge build-up can be negative in some parts and positive in other parts. These opposite charges are attracted to one another. When the attraction between the positive and negative charges grows strong enough, the charges travel through the air as lightning.
While most lightning happens within the clouds (cloud to cloud lightning), some of the time electric charge also builds up in the ground below the cloud and so the charges travel through the air between the cloud and the ground (cloud to ground lightning).
What about thunder?
As the electricity of the lightning strike travels through the air, it makes the air heat up and expand very quickly. This generates a shockwave of moving air that we hear as thunder. Low rumbling thunder is the sound of the initial shockwave echoing through the clouds.
How does the Tesla coil make lightning?
The Tesla coil is plugged in and gets its power from a power station (like the appliances in your house). It contains electrical transformers (which increase the voltage to between 2 and 2.8 million volts). This electricity runs around the flat coil at the bottom, which magnetically charges the tall upright coil. When the tall coil builds up enough electricity, it escapes from the top of the coil, down to the ground, taking the easiest path it can.
The Tesla coil uses current electricity and runs for a long time, but is much less powerful than naturally-occurring lightning. Natural lightning is generated by static electricity, is very powerful and does not last long. This difference means that Tesla coils can help determine which objects are more likely to be hit by lightning, but cannot be used to test how much damage would be done to objects by a lightning strike.
What makes a material a good conductor?
Everything around us – even your own body – is filled with electric charges. For electricity to easily pass through a material, the material must have lots of free electrical charges. We call the easy paths for electricity good conductors of electricity. Electricity always travels along the easiest path.
Metal has lots of electrical charges that can move freely, so electricity passes through it easily (it is a good conductor). Materials like rubber or glass have few free charges, so electricity has difficulty travelling through them. We call these materials insulators.
What about the rubber car tyres/rubber boots?
Rubber is an insulator, which means electricity has difficulty passing through it. Rubber is good at protecting against weak sources of electricity, but not powerful ones like lightning. A lightning bolt can contain millions of volts of electricity and has already travelled through several kilometres of air (which is also a good insulator), so a few centimetres of rubber will do almost nothing to stop it. The best way to stop lightning is to make sure it has an easier path somewhere else, like through a metal lightning rod.
What's the cage for?
The metal cage surrounding the high voltage equipment is called a 'Faraday cage'. It protects us from the electricity produced by the high voltage equipment inside. It also blocks radio waves or magnetic fields produced by the high voltage equipment, which can interfere with electronic devices like your mobile phone.
If I touch the cage after the tesla coil has stopped, will I receive a shock?
No. The cage is connected to the ground, which allows the electricity to quickly travel through the cage to the ground, where it is safely dispersed and can dissipate.
Why is a human body a better conductor of electricity than wood?
The human body is mostly made of water, with lots of salts and other chemicals dissolved in it. These dissolved salts and chemicals mean there are lots of free electrical charges that can move around. Dry wood has less dissolved salts and chemicals, so electricity cannot travel through it so easily.