– [Instructor] Electromagnetism or the electromagnetic force
is one of the four fundamental forces of nature.
It generates light and energy and holds atoms,
matter, and the world as we know it together.
Electromagnetism is a branch of physics
that studies the interactions between electric
and magnetic fields.
All matter has an electric charge
which can be positive, negative, or zero.
Opposite charges attract while like charges repel.
These electric forces bring and hold atoms together.
And when atoms gain a positive or negative charge
through the transfer of electrons,
a measurable electric field will form.
If those electrically charged particles start to move,
the field will become a flowing electric current
and form a magnetic field around it.
Under the right circumstances, interacting electric
and magnetic fields can continuously produce
and sustain one another.
This generates an electromagnetic field
that transmits waves of electromagnetic energy,
or radiation, into space.
The intensity of this radiation is determined
by its frequency.
These frequencies make up what’s known
as the electromagnetic spectrum.
Near the middle of the spectrum is visible light
such as light emitted by stars, fireflies,
and computer screens.
On either side are invisible electromagnetic waves.
On one end are long, low-frequency radio waves
that broadcast television and radio signals,
microwaves that carry telephone signals and cook food,
and infrared waves emitted by fires.
On the other are short, high-frequency wavelengths:
ultraviolet, X, and gamma radiation.
Unlike low-frequency waves, these waves
can pass through the human body making them useful
for medical applications.
While electromagnetism has daily applications,
it’s also the engine that drives the planet as a whole.
Thousands of miles below the Earth’s surface,
a layer of liquid metals churn and flow.
This generates electric currents that then produce
magnetic fields that all together encompass
the entire planet.
Called a geodynamo, this process causes Earth’s poles
to attain positive and negative charges
turning the planet into a giant electromagnet.
This phenomenon also creates a protective layer
around the planet that shields us
from the most harmful radiation in space
leaving us to enjoy a world held together
by the strange and fundamental force of electromagnetism.
