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Tesla Coils
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This section contains a wide selection of articles showing how devices or experiments can be done at home.

Exploding Water

Exploding Water

Exploding Water ExperimentThis experiment demonstrates how a substance can change from a liquid to a gas in an instant! A cup of hot water will immediately explode when a small amount of a very cold alcohol based substance is added. Great care must be taken when performing this experiment, and the cold liquid should be added remotely or from behind a safety screen.

As soon as the liquid is added the entire cup of water will explode launching hot water and probably the cup into the air, so it is important to wear safety goggles and to be a good distance away when it happens.

The liquid is an alcohol based aerosol called ‘Tetrafluorethane Dimethyl ether’. The ‘Dimethyl ether‘ part is an organic compound used as propellant in other aerosols and is used with propane for cryogenic freezing.

This substance is found in aerosol cans in DIY or electronics shops but its expensive at around £10. It is commonly used for rapidly cooling electronic parts, removing chewing gum, or for freezing water in pipes that need to be cut. In the shops it can usually be found under the name “Freezer Spray”.

How it’s Done

The freezer spray is designed to evaporate rapidly as it is sprayed onto a surface as this draws heat away from it very quickly. For this experiment the freezer spray must be collected in liquid form before it can be used.

collecting the sprayThis is done by holding the nozzle in the plastic lid or similar container like shown on the left. The button is then pressed lightly so that the spray starts to come out slowly and collect in the lid. The first bit of liquid will probably evaporate quickly, but as the lid cools down it becomes easier to collect. The amount to collect will depend upon how big the cup of water is and how long it takes to go from collection to adding it to the water.

Once the liquid is collected it is tipped into a cup of hot water at a distance. It is important that the collected freezer fluid is tipped in at once and not dripped in. If it is added too slowly it will just eemptying the liquidvaporate before any violent reaction can occur.

Sometimes only fizzing and sputtering occurs, but when done correctly the reaction is immediate and quite powerful.

Important Safety Notes

 The water needs to be hot but not boiling or hot enough to scald.
– The cup holding the hot water should be a light weight plastic type like those from a vending machine.
– The freezer spray should be added to the water away from people, animals, or anything else that would be damaged by hot water.
– The spray should be used outdoors in a well ventilated area away from sources of ignition.
– Safety goggles, gloves and other protective gear are recommended to avoid injury from spilling or

Breakdown of a Capacitor

Violent Discharge of Static Electricity

Damaged FilmThe reflective film used to make one way windows can react quite violently to high DC voltages. The image on the left shows a piece of window film after being exposed to around 30kV from a low current voltage multiplier.

The film is composed of a plastic sheet coated with a fine layer of metal on one side. When placed plastic side down on the top of a voltage multiplier or Van de Graffe generator, it will act in a similar way to a capacitor. If a grounded electrode is placed near to the metal surface the effectiveness of the ‘capacitor’ will increase dramatically until the dielectric material breaks down, or the air breaks down allowing an arc to pass over the the surface of the plastic layer.

When this breakdown occurs the silver material and some of the dielectric are blasted into the air, leaving full transparent patches on the foil. When the film is removed from the HV power supply, it can retain a reasonable charge. The charge can be randomly distributed around the surface and you may still get a zap from a pieces that seem to have been discharged. The best way to tell if a piece is still charged, is to see if is sticks to things. A highly charged piece will be strongly attracted to other surfaces.

1400xHV Fractures

The images above show a microscopic view of the film after it has been violently discharged. The dark material is the metal, and the light is just the remaining plastic. At the top of the left image is the bulk of the metal. Under higher magnification we can see that this area also contains very fine fractures, as shown on the right

Tesla Coil Experiments

Tesla Coil Experiments

A homemade Tesla Coil is great for special effects style science experiments. The high voltage, high frequency output can cause strange effects in all sorts of materials. The Tesla Coil used in these experiments has a pipe inside the centre of the secondary coil. This pipe allows gas to be emitted from a small hole in the topload sphere.

Electricity and Fire

Fire is a type of plasma, as the constant exchange of electronic bonds between the molecules and the release of energy allows electrons to move around under the influence of an external electric field. Fire is considered as a ‘cold plasma’ because it temperature is relatively low when compared to electrically generated plasmas. A small flame from butane gas emitted form the top of the Tesla Coil acts as a discharge terminal or breakout point. The hot gasses rising from the flame also provide a further conductive channel.

Fire and High VoltageFire and High VoltageThese images show how the electrical hot plasma from the Tesla Coil blends with the cold plasma of the flame. Click on the photos for a full view.

The rightmost image shows the electrical discharge through a hot jet flame like that of a bunsen burner. This flame causes the arc to stay mostly in one filament until the turbulence becomes too great.

See more photos of plasma on the plasma page

Noble Gases

The Noble gasses (often referred to as inert gas) are often used to make plasma because they will not react with the electrodes or surrounding material. Different gas types have different ionization voltages, and will also emit different colours of light.

Neon Gas and Tesla Coil

Neon Gas and Tesla CoilNeon Gas and Tesla CoilThese photos show what happens when pure Neon gas is emitted from the top sphere of a small Tesla Coil. Neon has a much lower ionization voltage than air, so the gas will glow very brightly creating a plasma column to allow the arcs to be much larger. The picture on the right looks similar to the ‘death ray’ devices used in the movie War of the Worlds! You can see when tuned correctly the individual filaments tend to form multiple helices, allowing the plasma column to rise quite high.
See more photos of plasma on the plasma page

We can see from these images that the Neon only helps to increase the length of the plasma filaments when it is still relatively concentrated. The neon is not ‘burnt’ or consumed, but it quickly mixes with the air, and its effects on the plasma become negligible.

The top left video clip shows a TC with a perspex hemisphere loosely covering the top. When Neon gas is emitted from the top sphere it is forced to spread over the surface before escaping. You can see how the neon layer glows red. The next clip of a spontaneous single filament shows the TC in normal operation.

The erratic flowing arcs spontaneously disappear then return as one single extra long arc. The last two clips show how the gas affects the TC when it is emitted directly from the top of the metal sphere

Kelvin’s Thunderstorm

Kelvin’s Thunderstorm

Kelvin's ThunderstormThis is a device is a simple method for generating a high voltage charge or static electricity. It works by dripping water through an arrangement of metal containers and loops of wire.

Water, like many molecules is in the form of a dipole. This means that it has a difference in electric charge from one end to the other. The chemical formula for water is H2O, meaning there are two Hydrogen atoms and one Oxygen atom in each molecule.

h2oYou can see from the image on the right the way that the H2+ is more on one side therefore making an uneven distribution of charge i.e. a dipole. This is what gives water all its interesting properties such as its powerful solvent abilities and its ability to stick to other materials.

This experiment works best with pure or deionised water as it is a very good electrical insulator. Tap water contains dissolved ions which become mobile allowing the water to conduct electricity. 

As the streams of water droplets pass through the rings, charges are induced making the drips and ring oppositely charged. If a water droplet is made more negative it will help to make the drops on the other side more positive because of the cross connection between the collector cans and the metal loops. This process continues to cause the voltage to rise until the water drops start being deflected by the strong fields or a spark is produced.

The top containers can be made from plastic but it may work better if they are made from metal and connected to ground.

Electrostatic Motor

Static Electricity Motor

A CD with one side covered in foil can be made to spin at high speed by using static electricity, or high voltage DC. With the CD on a spindle with the foil side up, areas under the CD can be charged by nearby electrodes. If the electrodes are placed either side of the CD and just underneath it, charge will be deposited on the plastic surface of the disk.

Electrostatic MotorThe plastic disc is non conductive, so in order for the charge to get to the other electrode (of opposite polarity), the disk its self must turn. This physical transportation of charge still constitutes a current flow, even though the current does not flow within the material itself. The flowing current is directly proportional to the speed of the rotating disc.

Franklin’s Bells

Franklin’s Bells

Franklin's Bells DiagramIn 1752 Benjamin Franklin was experimenting with one of his inventions, the lightning rod. Using the setup shown on the left Franklin was able collect electrostatic charges from the wind above his house. No known images exist of the original setup used, but this is the most common method used to reproduce the effects he describes.

This electrostatic device was actually invented in 1742 by a German professor named Andrew Gordon. Gordon’s Bells were the first device that converted electrical energy into mechanical energy in the form of a repeating mechanical motion, opening the doors for a variety of modern technology, from security alarms to school bells.

Two metal bells are suspended on insulating (dielectric) supports. One bell is electrically connected to the earth and the other is connected to a lightning rod. A metallic ball is suspended between the bells by a dielectric thread. The lightning rod would allow charge to build up on the bell which would then attract the metallic ball. When the ball hits the first bell it will become charged to the same potential and therefore will be repelled again. Since the opposite bell is charged oppositely this will also attract the ball towards it. When the ball touches the second bell the charge is transferred and the process repeats.

Franklin himself wrote that sometimes the bells would ring when there was only a dark cloud above and no obvious thunder and lightning. A nearby lightning flash could cause the bells so stop ringing immediately. At other times the bells would be silent until a nearby flash of lightning started them ringing.

Franklin's Bells AnimationThis setup was used by Franklin to collect electric charge for use in other experiments. The amount of charge collected was sometimes so faint that after a spark between the bells it would take considerable time to charge up again. At other times a continuous stream of sparks could be obtained even at lengths of around 20cm.

These sparks could very dangerous and a direct strike to the lightning rod could cause explosions and fire. A safer version of this experiment is easy to setup by using a simulated lightning rod in the form of a high voltage DC power supply such as a Van De Graff generator or Voltage Multiplier.

If you don’t have some bells available then they can be replaced by any metal object such as a drinks can. This experiment works best if all the conductors are smooth, but a foil coated plastic ball will be ok if another type of lightweight metal ball is not available.

Diamagnetic Levitation

Diamagnetic Levitation

Diamagnetic Levitation SetupDiamagnetic materials are those that will repel magnetic fields. Many common materials such as water are diamagnetic, but the effect is usually so weak that only super strong magnetic fields will cause any noticeable effect.

The famous experiment where scientists were able to levitate small animals such as frogs used an incredibly powerful electromagnet to create a magnetic field strong enough to cause the water in the animals to be repelled. Electromagnets like this one draw huge amounts of electric current and therefore need extensive cooling. The structure its self must be very strong to prevent it from crushing its self. This makes it virtually impossible for such an experiment to be done at home or in the school science class.

The experiment shown here does not cause a diamagnetic material to levitate, but it is used to help levitate a small magnet. The diamagnetic material used is Bismuth as it is one of the best diamagnetic materials available.

Bismuth can be obtained from most ‘Lead Free’ fishing weights or gun shot. It is very similar to lead, and can be melted easily. For this experiment it is necessary to create two blocks of bismuth. When a small magnet is placed between these blocks it will experience a small force from above and below. These forces alone are too weak to lift the magnet so some larger magnets can be placed above to help counteract gravity.

The large magnets are placed on a screw mechanism so that hey can be finely adjusted in height. It will need to be carefully adjusted until the magnet begins to levitate. The space between the two pieces of Bismuth should only be a tiny bit larger then the magnet in between.

Curie Effect

Curie Effect Demonstration

Curie Effect SetupThe curie effect usually refers to a magnetic phenomenon discovered by Pierre Curie. He discovered that ferromagnetic substances exhibited a critical temperature transition, above which the substances lost their ferromagnetic behaviour. This is now known as the Curie point.

A simple experiment, often named ‘the curie effect heat engine’ is a great way do practically demonstrate this important scientific principle.

A ferrous metal object such as a screw is suspended by a length of stiff wire so that it can swing freely from left to right.

To one side of the pendulums swing, a magnet is fixed into a position where it attracts the mass on the pendulum, and holds it up preventing it from swinging. The magnet must be far enough away so that it holds the mass up, but without actually touching it.

When a heat source such as a candle is place under the ferrous mass, the temperature of the material will increase until it reaches the curie point. When this occurs the thermal noise in the material prevents it from being held by the magnet and it will swing away. This will quickly allow the mass to cool and on its return swing (or before) the magnet will pull the mass back over the heat source, causing the whole process to start again.