In 1755, Benjamin Franklin, curious about
the workings of electricity, began testing
various hypotheses.
In one of his experiments, Franklin took an
electrified silver can and dangled an uncharged
cork ball (attached to a non-conductive silk
string) into the can.
The cork ball was not attracted to the interior
of the electrified can.
Puzzled, Franklin withdrew the cork ball from
the interior of the can, and instead brought
it close to the exterior of the can.
The ball was immediately drawn to the can’s
exterior surface.
How could the same electrified can attract
a cork ball from its exterior but not its
interior?
Franklin never discovered the answer.
Fast forward about eighty years as the workings
of this puzzle started to become clearer.
In 1836, English scientist Michael Faraday
made a similar observation to that of Franklin;
when charged, an electrical conductor - like
Franklin’s can or a metal cage - would display
that charge only on its exterior, not on its
interior.
To further test this observation, Faraday
conducted an experiment, similar to Franklin’s.
Faraday lined the exterior of a room with
metal foil and charged it with an electrostatic generator.
He then used an electroscope - a device that
detects electrical charges - in the middle
of the foil-lined room.
As he had predicted, the electroscope detected
no electrical charge within the room.
To understand how this works, one must first
understand the basics of electricity and conductors.
First, conductors are metal objects that have
electrons - negatively charged particles - that
move around them.
In the absence of an electrical charge, the
conductor has roughly the same number of positively
charged holes and negative electrons.
However, if another object with an electrical
charge nears the conductor, the positive and
negative components separate.
If the foreign object has a negative charge,
the negatively charged electrons are repelled.
If the foreign object has positive charge,
the negatively charged electrons are drawn
to that foreign object.
This process is called electrostatic induction.
With the foreign object present, the positive
and negative particles end up on opposite
sides of the conductor.
This essentially cancels out the field of
the external object’s charge inside the
metal conductor.
Therefore, the net electric charge inside
the conductive material is zero.
And, despite lacking a charge inside the conductor,
the opposing electric field blocks out electromagnetic
radiation; the extent of this blocking out
is dependent on the cage’s construction,
the size of its holes, its material, and so
on.
The uses of these Faraday cages are extensive
and various.
One of the most well-known applications is
for airplanes.
Airplanes are frequently struck by lightning
which could harm the passengers and quickly
damage the electrical components onboard.
However, this doesn’t happen because of
the plane’s aluminum hull; the charge of
lightning strikes and passes over the hull
without any inflicted damage.
Furthermore, Faraday cages that are the size
of rooms are often used as private locations
for sensitive information to be shared; eavesdropping
devices cannot penetrate the room.
Militaries even use Faraday cages to protect
their sensitive electronics from EMP’s which
could destroy their vital systems.
Faraday cages’ usage further ranges from
microwaves to MRI machines.
Taking an advantage of a simple rule in physics,
Faraday cages undoubtedly play an important
part in daily life.
Before I end the video, I wanted to say a
quick thank you.
At the time of this script, I have just passed
2,000 subscribers, an amount I quite frankly
thought would take much longer to reach.
You guys are awesome, and I hope you have lovely day.
