- You might've seen the crazy cool demonstrations done
with Tesla coils, but how do they actually work?
Well, to really answer that question,
I'm gonna discuss how all the parts of the Tesla coil
were discovered and why.
Ready for a whirlwind study of electronics?
Put on your thinking caps and let's go.
♪ Electricity, electricity ♪
This story begins way back in 1826.
That's when a retired soldier
with some pretty amazing sideburns named William Sturgeon
discovered that if current runs through coils of wire
around an iron bar, the iron bar acts like a magnet
and can attract metal.
This was logically called an electromagnet.
Six years later in 1831,
Michael Faraday decided to try to see
if he could make electricity with magnets.
He was not having much luck
with the weak magnets available at the time,
so he decided to play with electromagnets.
He had two separate coils wrapped
around a single iron ring and found that when he attached
or disconnected a battery to the first wire,
the second wire would get a jolt of electricity.
Faraday then came up with the idea of magnetic field
and the theory that changing the magnetic field in a coil
would create or induce a current in the wire.
Faraday was a little disappointed, however,
that he could never feel the jolt of electricity
from the second coil.
Remember, electricity was in its infancy,
and using themselves as human guinea pigs
was one of the few available devices at the time.
A few years later, an Irish priest and amateur scientist
named Nicholas Callan wondered
if he could tweak Faraday's device
to make something that could give a good shock.
When he wound both coils around the same iron bar,
but kept them electrically separate,
he could feel shocks from wires
that were not electrically connected to a battery.
He found it was even more impressive when the primary wire,
the one connected to the battery, was thick
and the secondary coil was really thin
and wound around as many times as possible.
Callan didn't know it,
but he had just invented the step-up transformer.
See, when he connected a battery to a coil,
the coil became an electromagnet with a magnetic field.
When he disconnected the battery,
the coil lost its magnetic field.
Therefore, according to Faraday's
brand new law of induction, every time that Callan connected
or disconnected the battery,
it creates new current in the secondary coil.
If the secondary coil has fewer loops than the primary,
you get more current, but less voltage,
which is why Faraday could see the current,
but could not feel the voltage.
Callan, on the other hand, produced a system
with far more loops in the secondary coil,
so he created more voltage and more shocks,
but also less current.
Callan also created a wheel
to mechanically connect and disconnect the battery
and was very pleased to note with just this repeater,
two coils, and an iron bar,
he created, according to him, quote
"the best magneto electric machine ever constructed."
Callan sent a report to his friend, William Sturgeon,
the same man with the amazing sideburns
who had invented the electromagnet in the first place.
Sturgeon and his friend, George Bachhoffner,
made their own versions of Callan's machine
with a better repeater and bundles of wire in the core
instead of a solid iron bar.
And for many years, many people made a fortune
out of selling these torture devices.
The induction coil was incredibly popular,
especially for giving medical cures.
Depression, migraines, infertility, fertility,
all could be solved with electric shocks.
Now the race was on
to make a bigger and more constant shock or spark.
One of the biggest advancements was using the coil itself
to disconnect and connect to the battery,
instead of using a wheel and a crank that you spun.
See, when there is current in the primary coil,
it acts like a bar magnet.
And so, the current carrying wire
can electrically pull a switch on the spring
to turn off the current.
Of course, once the current is removed,
the coil no longer acts magnetic,
so the switch is then released, which causes current to flow
in the wires again, which pulls on the switch again.
These would vibrate around 20 to 40 times every second
and was called an electric interrupter.
However, the electric interrupter would sometimes spark.
This is why, in 1853, a French physicist
named Armand Hippolyte Fizeau
placed something called a Leyden jar, or a capacitor,
next to the interrupter to absorb the side spark.
A capacitor is any object
with two large conducting materials
separated by an insulating material.
Leyden jars were the first type of capacitor
and are made by coating a glass jar with metal,
as glass is insulated.
Capacitors can store a large amount of charge
on its surfaces, depending on the size of the metal surfaces
and the thickness of the insulator.
However, by adding a capacitor,
Fizeau wasn't just getting rid of an unwanted side spark,
he was also creating a totally different device.
He was creating a device that took direct current
from a battery and made bursts of alternating current.
How did a simple jar do that?
Well, let me explain.
Imagine you charge up a Leyden jar with a battery
so that it has an excess of electrons on one side
and a deficit on the other.
If the sides are then connected with a wire,
the electrons will flow in a burst of current
and the jar will become discharged.
All well and good.
However, imagine that the wire has a part that is coiled up.
Then, the burst of current goes through a coil
and creates a change in current in a coil.
Changing current in a coil
changes the magnetic field in the coil,
which induces a new current in the coil.
This is called self-inductance.
Therefore, when you discharge a Leyden jar through a coil,
the current keeps on flowing
even after the jar is discharged.
The result is that the jar ends up
with extra charge in the other orientation.
Eventually, the current stops,
but then the Leyden jar is charged the other way
and the current begins to flow in the other direction.
In a perfect system without resistance,
the current will just flow back and forth forever.
However, with resistance, the current goes back and forth,
getting smaller and smaller with each oscillation
until the system is fully discharged
with no current flowing.
A capacitor connected to a coil is called a tank circuit
and is used even today to make oscillating current.
The frequency of the oscillation depends on the properties
of the capacitor and the coil.
If you wanna change the frequency,
you can just change the length of the coil
or the shape of the capacitor.
In this way, in the 1850s,
they could take current from a battery
and make bursts of waves that we're oscillating
at millions of times per second, or in the radio range.
Of course, it took many years for scientists
to come up with the theories and equations
for how a tank circuit worked.
And it wasn't until 1886 that a German scientist
named Heinrich Hertz added an antenna to his induction coil
and created the first human-made radio wave.
However, Hertz had no interest in industry.
He thought his experiment was solely
to prove the existence of electromagnetic waves.
Now, we finally get to Nikola Tesla.
Woo!
In the summer of 1889,
Nikola Tesla went to the World's Fair in Paris
and heard about the miracle
of Hertz's experiments with radio waves.
Experimenting himself, he started to tinker
with the induction coil and had the happy inspiration
of removing the interrupter and the DC battery
and replacing them with an alternating or AC generator.
This actually makes perfect sense.
Why use a battery and a mechanical switch
to turn current on and off when you can just use a generator
that automatically switches the current
from one direction to the other?
Also, this was after Tesla had just invented the AC motor
and the three-phase AC generator,
so he had AC on the mind, so to speak.
Tesla found that it worked, but it worked too well.
It overheated the iron core
and it actually melted the insulation off the wire.
Tesla then found that it worked well
even without an iron core, so he used an air gap instead.
He then found that the Leyden jars next to the primary coil
sometimes worked and sometimes interfered.
Therefore, he moved the jars to the secondary circuit
and made them adjustable.
By placing the capacitors in the second circuit,
he could tune the vibration of the coil and the capacitor,
the tank circuit, to multiple of the frequency
of the original alternating current from the AC generator.
In this way, the Tesla coil created a high frequency,
high voltage, alternating current.
If he put an antenna on the secondary circuit,
it would've created tuned, high frequency radio waves.
However, Tesla wasn't interested
in wireless telegraphs or wireless communication.
He was interested in wireless lighting.
For that reason,
Tesla added another resonant electric circuit,
a new circuit with sets of coils
that could light lamps with a single wire.
He then found that neon and fluorescent tubes
would light when they were just held
near the coils without any wires at all.
Finally, Tesla found that
if he put a metal toroid on top of the coil,
it would produce the most beautiful sparks and discharges,
which is what a Tesla coil is mostly used for today.
Let me go over how a modern Tesla coil works
and how it makes such a beautiful show.
Remember, if you change the current in one coil,
it will create a current in an adjacent coil.
And if you have more loops,
you get more voltage and less current.
Also remember that if you discharge a capacitor
through a coil, you get an oscillating current.
Tesla coils start with the AC from the wall.
Then, they use a step up transformer,
which is made of two parallel coils
that increase the voltage and decrease the current,
just like Reverend Callan discovered in the 1830s.
This creates an alternating spark in the spark gap,
which causes the primary capacitor to repeatedly charge
and discharge, which in resonance with the coils,
creates high-frequency waves.
This high frequency, high voltage current goes
through the primary coil and induces an even higher voltage,
high frequency, super low current in the secondary coil.
This process can produce millions of volts and in the torus.
This voltage is so high
that the electrons around the torus can become free
and can transmit electricity.
This is called ionizing the air,
which allows for dramatic discharges of electricity.
Tesla loved the beautiful demonstration,
but he also had a dream to use his coil
to electrify the earth and the atmosphere
and make us all glow,
which turns out to be physically impossible.
He even convinced JP Morgan to fund it.
However, a man named Marconi had a more modest goal
to send a wireless telegraph signal across the ocean.
And he used Tesla coils to succeed.
How Marconi created a wireless empire
and won the Nobel Prize and destroyed Tesla in the process
is next time on The Secret History of Electricity.
♪ Electricity, electricity ♪
Thanks for watching my video.
I know I cover a lot of people in a lot of different times.
If you go into the comments section,
you'll see a timeline with links
to different videos I've made about different people.
Thanks and have a good day.
(upbeat music)