My PBL Project
Introduction:
For my PBL experiment, I have to construct 'Jacob's ladder' and infer how does the arc form and why. It is basically a high voltage device which can be used to demonstrate an arc, produced with the use of the high voltage, traveling up two electrodes.
Materials:
High Voltage Power Source
Thin Cooper tubes
Non-conductive/ non-flammable base
High-Voltage wire
Procedure:
Attach the cooper tubing (electrodes) to the base. Make sure that the bottom of the electrodes stick out from under the base, also that they gain a bit more distance between each other the further away it is from the base.
Use the high-voltage wire (outputs) to connect the end of the cooper tubes at the bottom of the base to the power source.
Turn it on, and enjoy!
Scientific Principle:
A Jacob's ladder (more formally, a high voltage traveling arc) is a device for producing a continuous train of large sparks that rise upwards. The spark gap is formed by two wires, approximately vertical but gradually diverging from each other towards the top in a narrow V shape. It was named for the "ladder to heaven" described in the Bible.
When high voltage is applied to the gap, a spark forms across the bottom of the wires where they are nearest each other, rapidly changing to an electric arc. Air breaks down at about 30 kV/cm, depending on humidity, temperature, etc. Apart from the anode and cathode voltage drops, the arc behaves almost as a short circuit, drawing as much current as the electrical power supply can deliver, and the heavy load dramatically reduces the voltage across the gap.
The heated ionized air rises, carrying the current path with it. As the trail of ionization gets longer, it becomes more and more unstable, finally breaking. The voltage across the electrodes then rises and the spark re-forms at the bottom of the device.
This cycle leads to an exotic-looking display of electric white, yellow, blue or purple arcs, which is often seen in films about mad scientists. The device was a staple in schools and science fairs of the 1950s and 1960s, typically constructed out of a Model T spark coil or any other source of high voltage in the 10,000–30,000-volt range, such as a neon sign transformer (5–15 kV) or a television picture tube circuit (flyback transformer) (10–28 kV), and two coat hangers or rods built into a V shape. For larger ladders, microwave oven transformers connected in series or utility pole transformers (pole pigs) run in reverse (step-up) are used.
Traveling-arc devices are dangerous. The sparks can burn through thin paper and plastic and start fires, and contact with the exposed high-voltage conductors can be lethal.
Investigation Questions
1.) Why does the Arc form?
The 'arc' that appears whenever the ladder is turned on is due to the fact that there are electrons passing through the copper wires. These electrons are trying to get away from each other, which results with them 'jumping' from wire to wire back and forth. Everytime these electrons jump from wire to wire, allows us to see the spark that takes form. As the hot air rises, the spark follows after, once the spark reaches the top, it dies and and a new one appears at the bottom. This small spark is very hot, and can be considered as plasma.
2.) Why does the wave travel upward?
The arc is able to travel upward with the help of the warm air; ionize air radiating off from the arc is at a lower resistance compared to the hot air, which allows the Arc to move upward rather than downwards or staying in the same place. Paschen's law is what pretty much explains just how the transformer is able to create this arc of electricity across these two copper tubes.
3.) What is Paschen's Law?
Paschen's law is basically what voltage is needed in order to ignite a discharge- or in this case an electrical arc, in between two electrodes with the help of both gas and distance in between.
4.) Why does it make that noise?
The arc produces a static like noise as the spark travels up the ladder before finally reaching the top, and dying before starting up all over again. This is due to the electric current passing through tube as well as the millions of electrons jump from wie to wire, trying to get further away from each other.
Safety Regulations:
Since this project does in fact include the use of both high voltages, and currents that can be considered as lethal. For this, I have to make sure that nothing nor no one should come in contact with the ladder or the transformer. For this, I and other possible bystanders, have to keep a fairly large distance from the ladder in general.
The ladder must be used in a well ventilated area due to the fact that it can create Ozone in result to the electrical discharges. Also, one cannot stare at the arc for too long since it can result with with a blinding effect due to the amount of UV waves radiating off from the electrical arc.
