- What is light?
I was taught in high school
that light is an electromagnetic wave,
but what does that mean?
What does light have to do with electricity and magnets?
Well, I think the best way to understand it
is to talk about why and how
Michael Faraday dreamed up this wild idea way back in 1846.
This is a story of internalized sexism
of presumptuous college students, mysterious crystals
and a very fortuitous case of stage fright.
Ready?
Let's go!
♪ Electricity electricity ♪
On February 2nd, 1826,
a Scottish woman named Mary Somerville
published a paper on her experimental research
in the philosophical transaction,
becoming the first woman to publish experimental work there
in its 161 year history.
Years earlier, an Italian named Morichini
claimed that he could magnetize iron bars
with ultraviolet light,
but no one else seemed to be able to repeat his experiment.
However, Somerville said she found a way
to use bright sunlight to magnetize needles.
This was six years after a Danish man named Oersted
had found the current in a wire can move a magnet
or current in a wire creates a magnetic force.
Therefore it seemed logical
that the different forces would be related.
Light, electricity and magnetism.
Unfortunately, three years later,
her experiment was disproven.
Devastated, Somerville burned all copies of her work
and decided experimental research was impossible
because as everyone had told her women can't do research.
She bemoaned quote, "Originality is not granted to my sex.
"We are of the earth.
"Original genius in science is hopeless"
Somerville went on to publish articles and books
on mathematics and other people's research and science
but basically gave up on conducting her own research
from that time on.
Fast forward, 17 years to 1845.
Michael Faraday was 54 years old
and was already famous for his discovery of the first motor,
the idea of magnetic fields
and induction as well as thousands of other discoveries.
He also suffered from severe depression and memory problems
as well as possibly mercury poisoning,
a common affliction for scientists at the time
as they didn't know the dangers of mercury.
He was therefore spending
very little time in the laboratory.
This is when a baby face 21 year old math student
named William Thompson later knighted Lord Calvin
presumptuously wrote Faraday
and asked him if he'd ever chained something
called the polarization of light with magnets or electricity
when the light was going through a transparent material.
Faraday was intrigued.
Ever since Morichini
and Somerville's disasterous experiments,
Faraday had been trying and failing to alter magnetism
with visible light or to alter light with magnetism.
He'd even previously tried to change
the polarization of light,
but never while the light was going through a material.
Inspired, Faraday went back into the lab.
What is polarization?
Well, imagine you're making a wave
on the rope to make the wave on a rope.
To make the wave, you can move your hand up and down
and the wave would move away from you down the road.
However, if you wish,
you could also move your hands side to side.
The direction of vibration
is called the polarization of the wave.
Most liked is what is called unpolarized
or randomly polarized,
meaning that some is vibrating up and down,
some side to side,
and even some in clockwise and counterclockwise circles.
In 1815, a Scotsman named David Brewster
found an equation for an unusual phenomenon.
If light reflects off a surface at a low angle
currently called Brewster's angle,
then all of the reflected light will be polarized parallel
to the surface or all of the light
will vibrate parallel to the surface.
This is why polarizing sunglasses work so well.
They block the horizontally polarized light
which is the light reflected at low angles.
Also called glare.
Now we come to a strange object called an Iceland crystal.
When light goes from air into a transparent material,
the light slows down and bends.
Iceland crystals are unusual because the amount
the light bends depends on the polarization of the light.
Therefore when white light enters the crystal
it bends the light into two beams.
One that vibrates vertically
and one that vibrates horizontally.
As humans can't distinguish polarization
with their naked eyes,
the crystal makes two images.
In 1828, another Scotsman named William Nicol
made the last piece of the puzzle.
He wanted to use Iceland crystals
to remove one polarization entirely
or to make the first polarizing filter.
He called it a polarizing prison.
He cut an Iceland crystal into an angled rectangle,
then cut that into two triangles,
then glued the triangles back together.
Like all Iceland crystals,
when light hits this prison, the light splits
into horizontally and vertically polarized light.
However, the horizontally polarized light is bent more
and the triangles and the glue are designed
in such a way that when this light hits the glue
all of the light is reflected.
This is called total internal reflection
and shines out the side.
The vertically polarized light, however,
bends less so that it bends through the glue
and thus passes safely through the prison.
Now we have all the pieces of Faraday's experiment.
Faraday shined light from the brightest lamp he could get
at Brewster's angle off a piece of glass
getting horizontally polarized light.
He then put a Nicol prism in the path of the light
so that it filtered out the horizontally polarized light
and he could no longer see the light from the lamp.
He then placed a strong electromagnet,
a magnet made with electricity,
next to a sample of glass and the path of the light.
When he magnetized the electromagnet
he could see the light from the lamp.
The magnetic field
had rotated the polarization of the light.
When he unplugged the electromagnet,
the image disappeared again.
Faraday wrote that he had,
"Established, I think for the first time,
a true direct relation and dependence
"between light and the magnetic and electric forces."
This as with Somerville,
the scientific community was excited to hear that light
and electricity and magnetism were linked
in one great universal principle.
However, unlike Somerville,
Faraday's experiment has never been disproven.
Also, unlike Somerville, when Faraday made mistakes
it was never attributed to his gender.
Faraday began thinking about what it meant
to have light linked to electricity and magnetism.
16 years earlier,
Faraday had created the idea of magnetic fields
or what he called lines of magnetic force.
Faraday's idea was that magnets and current
emanate lines of force that are visible
with little metal shavings.
Faraday felt that these fields explain magnetic forces.
For example, the reason the two Norths of a magnet repel
is because their magnetic fields push against each other
and the North and the South attract
due to their fields combining.
Faraday also felt that electric charges
also have lines of forces around them or electric fields
which can explain electric forces.
Even gravity has its own gravity field.
Faraday created a thought experiment.
Imagine two charges that are either electric or magnetic
and they're separated from each other
but are connected by their magnetic or electric fields.
If you vibrate one, the other one will feel the force
and vibrate as well.
Faraday imagined
that when the first object vibrated,
it effectively plucks the field
and creates a wave in that field
and the vibrating field
is what makes the second object oscillate.
Faraday then wondered
if light was just a wave of one of these fields.
This seemed like a pretty crazy idea
and Faraday was too reserved to express this
in a talk or a paper.
Then on April 3rd, 1846
Faraday was supposed to give an introduction to a lecture
by a man named Charles Wheatstone
but Wheatstone chickened out at the last minute.
Faraday stepped in for an impromptu talk
but he quickly ran out of material.
So to eat up the hour, he talk freely about
"the vague impressions of my mind".
Faraday told the astonished crowd
about his thought experiment, which led him to say,
"the view, which I am saying so bold to put forth
"considers, therefore radiation, i.e. light,
"as a vibration in the lines of force."
Faraday was quick to add
that these ideas were a little outlandish.
"Even to myself, my ideas appear only
"as a shadow of a speculation."
However, they'RE basically what we believe today.
We believe light is created when electrons,
which are negatively charged particles,
vibrate and create a pluck electric wave.
Also moving electric charges create a magnetic field.
So vibrating electric charge
simultaneously creates a pluck magnetic wave.
For this reason, light is called an electromagnetic wave.
When you see a red rose in the garden, for example,
that's because electrons in the sun vibrated,
which causes electrons in a rose to vibrate,
eight and a half minutes later,
which cause electrons in your eye to vibrate
which sends an electric signal to your brain of red.
But what is traveling between the sun and the rose
or the rose and your eyes?
A pulsed electromagnetic force field.
Crazy, huh?
- I didn't know that.
- So if light is partially a magnetic wave,
why did Mary Somerville's experiment magnetizing needles
fail in 1826?
Well, sunlight acts like a wave.
So the magnetic field is always oscillate.
Could sunlight then make a magnet vibrate?
Good question and no.
Sunlight has many different frequencies, i.e. colors,
and many different direction, i.e. polarizations.
So the magnetic force would be all over the place.
Even if you had polarized light at a single frequency,
like red laser light, it's still vibrates at around
450 million million times a second.
Way too fast for a magnet to respond.
If you're having a little trouble
understanding electromagnetic waves,
think of how they felt in 1846.
The Royal astronomer, Sir George Airy said,
"I can hardly imagine anyone
"who practically and numerically knows electrical theory
"that accepts anything so vague and varying
"as lines of force."
Faraay's strange theories might've come to nothing
if it weren't for young mathematical physicist
named James Maxwell.
In 1854, eight years after Faraday's talk,
Maxwell wrote to his friend William Thompson,
the same student who inspired Faraday
to conduct his polarization experiment in the first place,
asking for advice on what to read.
Soon Maxwell was pouring through
all of Faraday's experimental researches in electricity
and began to add the missing spice, mathematics.
How James Maxwell and his wife Catherine changed the world
with some really difficult mathematics
is is next time on "The Secret History of Electricity".
♪ Electricity, electricity ♪
Thanks for watching my video.
Please remember to give me a nice thumbs up.
I always like that.
Also, if you want more information
of how Faraday came up with magnetic fields
in the first place,
I have a video about that.
You also might be interested
in how Faraday escaped poverty to become a scientist.
That's a good story.
And check out the one about Maxwell.
It should be a good one and don't worry,
I don't actually talk about the math.
Okay, have a good day!
(soft jazz music)