The Demonstration: An electric spark jumps between two parallel wires. The spark then "climbs" up the ladder.
Quick Physics: The transformer at the bottom creates a potential
difference between the wires. The electrons repel each other, so they
jump from one wire to try and get as far apart as possible. The spark
heats up the surrounding air and hot air rises, so the spark rises with
it. When the spark gets to the top of the wires, it dies and a new one
starts at the bottom.
The JacobŐs Ladder is a relatively simple device. The big box on the
bottom is called a transformer. A transformer is something that changes
the voltage going to a device. You probably have several transformers
in you home; for example, the charger on your cell phone is a
transformer. Your cell phone converts the 120 Volts that come out of
the wall into 9 or 12 Volts. The JacobŐs Ladder converts the same 120
Volts to more than 500 Volts!
When the JacobŐs Ladder is turned on, electrons are fed into one of the
wires. These electrons want to get away from each other, so they jump
across to the other wire, which is connected to the ground. When they
jump, we see a bright spark in the air. The spark then climbs up the
ladder as it heats the air around it. Remember that hot air rises, and
in this case takes the spark with it. This spark is very hot, so hot
that it can be classified as a plasma (see Plasma Tube). Eventually the
spark dissipates and releases all of those electrons into the air.
Link to Teacher Resources
Page Updated 8/29/07