- How were radio waves discovered?
And what does that have to do with Maxwell's equations?
Well, all started with a pessimistic young scientist
named Heinrich Hertz, and a contest
he was too intimidated to try
and it ended with one of the most influential experiments
of all time.
Ready?
Let's go.
♪ Electricity electricity ♪
In 1879, Germany's most famous scientist,
Hermann Von Helmholtz had a great idea
for the yearly Berlin Prize
at the Prussian Academy of Sciences.
He suggested they offer the prize
to the person who could experimentally prove
the existence of electromagnetic waves in space.
Or to experimentally prove,
"the theory of electrodynamics,
which was brought forth by Faraday
and was mathematically executed by Mr Maxwell."
Helmholtz had a 22 year old grad student
that he thought was perfect for the job Heinrich Hertz.
Hertz thought about it but decided the problem
was too difficult for him.
However, it put the idea in his mind
and for many years he seriously studied
the physics of electromagnetic rates.
In fact, his diary had entire days
with single comments like,
"thought about electromagnetic rays,
nothing but electromagnets.
Worked on electromagnets all day.
Electromagnets still without success."
And my personal favorite
because I identify with it too well,
realize that "most of what I've found so far
is already known."
He ended 1885 with,
"happy this year is over
and hoping it will not be followed by another like it."
It turned out 1886 was a far superior year
both professionally and personally.
1886 was the year Hertz met a woman named Elizabeth Doll
and fell in love.
Also in the spring of that year
he was showing his equipment to his new fiance
and happened to know the spark created a distance away
from a discharging Laden jar.
Hertz was thus inspired to tempt the experiment
that intimidated him seven years earlier.
In 1887, Hertz found a way to experimentally validate
that light is not electromagnetic wave.
How did he do that?
Well, Hertz made a wave with vibrating electronics
and made it travel across a room.
He also later showed that his new wave would reflect
off mirrors like light,
bend through prism like light
and even moves at the speed of light.
Whoa, what was this new invisible light?
Well, by the 1920, these waves
which were originally called Hertzian Waves
were Christian radio, wait side comment.
When most people think of radio
they think of music, which is why many people
think radio waves are really sound waves.
This is wrong, radio waves
are invisible low frequency lightweight.
To explain this better, think of records and record players.
Records are discs made of vinyl with little bumps in them.
When the needle bounces on the bumps
it can be used to vibrate a cone and make music.
The record therefore is not made of music,
it's made of vinyl.
Radio waves are also not made of music
they are made of electromagnetic waves, just like light.
However, like the vinyl records,
they can have bumps in the waves
that can be used to create sound.
Anyway back to Hertz,
how did he make radio waves?
Well, luckily for Hertz, he had the device
called a spark gap generator
which would transfer the power from a DC battery
into bars a very high alternating voltage
and a large spark.
I will describe how a spark gap generator works
and how it was discovered in the next video.
All Hertz had to do to create
his invisible electromagnetic waves is adding the antenna.
So that's what he did,
he had it two wires to the spark gap generator
with metal spheres at the end.
Now he could create the waves
but he had to detect them as well.
For that he made a circular detector
with a little gap in it.
Wit the hope that if they caught the wave
they would create a little spark that he could see.
Hertz could then change the size of the gap
to give them a sense of the strength of the way.
This was not an easy experiment,
the sparks are microscopically short,
they only last about a millionth of a second.
It almost seems absurd and impossible
that they should be visible
but in a perfectly dark room, they're visible to an eye.
Upon this thin thread hung the success of our undertaking.
On November 5th, 1887, he hesitantly sent a copy
of his paper to his old boss, Helmholtz
"I have some misgivings about taking up your time
but this paper deals with the topic
that you yourself once urge me to tackle
some years ago."
Helmholtz his reply was immediate
a postcard that simply said,
"Bravo!
We'll hand it to be printed on Thursday."
Suddenly Hertz was on a roll.
His wife, Elizabeth wrote his parents
that the experiments were going swimmingly.
He simply pulls these beautiful things
out of his sleeve now.
Of course it makes him very happy,
and me as well.
When he tells me about it with a radiant face.
although he certainly understands nothing of it.
Hertz then notice that ultraviolet light
affected his results,
making him the first person to notice
the photo electric effect.
Then to Hertz the surprise, he noticed that
this new wave bounced off mirror
just like the visible light does.
So, Hertz set up a mirror parallel to the spark
so that wave would bounce back
and forth and make a standing wave.
Standing waves are distinguished by the fact
that they have points where the wave oscillates strongly
antinodes and points where the waves
destroy each other nodes.
Hertz moved his receiver between the antenna
and the mirror and noted that the spark in his receiver
would grow bigger at the anti nodes,
and would disappear at the node.
In this way, Hertz measured the wavelength of this wave.
He also knew from theory
that his spark gap generator produced
around 70 million waves per second
or 70 million Hertz named after Heinrich.
He then used the simple wave equation
that speed is frequency times wavelength.
In this crude way, he measured that the speed of his wave
was 320,000 kilometers per second
which is quite close to the speed of light,
300,000 kilometers per second.
No, he didn't break the speed of light,
he just had small inaccuracies
in his measurements.
Note that not only did Hertz verify that
light is an electromagnetic wave,
he made his own cast of special electromagnetic waves
that are invisible and have transformed our world.
Hertz paper gained him almost instant international fame.
William Thompson also known as Lord Calvin
who had influenced both Faraday and Maxwell
and their theory said,
"Hertz's electrical papers are permanent monument
of the splendid consummation of Faraday's ideas."
Hertz got the plum position as a full professor
at Bond University,
and bought a beautiful house with a slight catch
that it had previously been used for medical experiments
and might've been contaminated with chemicals.
Maybe for that reason,
or maybe for some other trick of fate,
Hertz began to have migraines in the July of 1892.
He was diagnosed with a blood disorder
and died on January 1st of 1894
when he was only 36 years old
leaving his distraught wife Elizabeth
and two young daughters age two and six.
It's tempting to think
that if it wasn't for his untimely death,
Hertz might've invented wireless Telegraph
or maybe even radio communication.
However at the time he didn't see any practical use
of his invention saying, this experiments are,
"of no use whatsoever, this is just an experiment
that proves Maestro Maxwell was right.
We have these mysterious electromagnetic waves
that we cannot see with the naked eye
but they are there."
A few months after Hertz is death
a 20 year old Irish Italian man named Marconi
read an obituary of Heinrich Hertz and became obsessed
with creating long distance wireless Telegraph.
However, he might not have gotten very far
with the spark gap generator as it was too weak
to transmit a signal crossed the ocean.
Luckily, five years later,
Nikola Tesla went to the world's fair in Paris
and heard about the miracle of Hertz's experiment.
Tesla then started tinkering with the spark gap generator
and ended up inventing the Tesla Coil.
But what exactly is the Tesla Coil?
How does it work and why is it important?
Well, I'll tell you next time on the secret
history of electricity.
♪ Electricity electricity ♪
Thanks for watching my video.
If you haven't seen them yet
I recommend watching the one on how Faraday came up
with the idea of electromagnetic waves,
and how Maxwell came up with the math for it.
Also check out the next one on Tesla Coil should be good.
Okay, have a nice day.
(upbeat music)