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Imagine a world where “with a device we can put in our vest pocket…through television
and telephony we can see and hear each other as if we were face to face,” where “motion
pictures can be transmitted wirelessly,” where “automobile carriages…can perform
operations involving…judgement.”
And where “electricity is generated centrally and transmitted over vast distances" to provide
power to homes and factories. That’s the world we live in today, and perhaps take
for granted.
But there was a man who imagined these impossible technologies more than a hundred years ago.
He along with Thomas Edison have arguably had more of an impact on the modern technologically
advanced lifestyle we enjoy today than any other scientists past or present.
That man is of course Nikola Tesla. Yet, this giant of imagination and innovation died nearly
penniless, and almost forgotten. But, there is no doubt that history has posthumously
rewarded him with the accolades and recognition that he richly deserves.
Perhaps Tesla’s biggest contribution to the world was his innovations in alternating
current technology, that allowed electrical power transmission over long distances, and
the invention of the AC motor that allowed this AC power to be used by factories and
businesses.
The adoption of this technology was an uphill battle because Thomas Edison’s DC or direct
current systems had been the standard early on.
Edison tried desperately to convince the world to go with DC and even staged an electrocution
of a convicted criminal by AC current, to show the public how dangerous AC technology
was. But AC eventually won out, because the underlying truth about the superiority of
any technology lies in the science. And science has an objective truth that is difficult to
silence.
What does science have to say about Edison’s DC vs. Tesla’s AC technology? In order to
explain this, I am also going to explain how electricity works in general, using a simpler
analogy of electricity flowing through a wire that you might find more relatable. And that is
water through a garden hose. That’s coming up right now…
Tesla was born in what is today Croatia. His father wanted him to be priest. But as
a teenager, Nikola was fascinated by math and physics, and instead became an engineer.
At 29, he immigrated to the United states with 4 cents in his pocket, but he had a recommendation
letter that got him a job redesigning direct current generators at one of Edison’s factories
in New York City.
Tesla only lasted about a year on this job partly because his ideas on alternating current
technology conflicted with Edison’s DC.
What is AC and DC anyway? And why is one superior to the other?
To understand this, you have to understand some basics about electricity. So, what is
electricity?
All materials are made of atoms. Atoms have a positively charged nucleus and negatively
charged electrons surrounding the nucleus. These electrons are bound to the nucleus due
to their electromagnetic attraction to the oppositely charged nucleus.
But electrons in the outermost shell of the atom, called the valence shell, can sometimes
become free due to external forces. These electrons that escape from the valence shell
are called free electrons. And they can move from one atom to another. This is what can
cause a movement of charge. And this flow of electric charge is what electricity is
all about.
Materials that allow many electrons to move freely are called conductors. And materials
that don’t allow much free movement of electrons are called insulators.
So for example, if you look at copper, you will notice that it has one electron in its
outermost or valence shell. This can quite readily become a free electron. That’s why
copper is a great conductor. If we force this electron to move, we create electricity.
An electrical current is the flow of free electrons from one atom to another.
There are three concepts that you should understand, if you want to understand electricity. And
these are current, voltage, and resistance.
All three are connected, if you change one, the others will change too. The relationship
between these three properties is described by Ohm’s law, named after German physicist
Georg Ohm. Voltage = Current x Resistance
These are not easy to visualize because you can’t see them. So we will use the analogy
of electricity as water.
Think of a water tank, with a hose attached to the bottom.
Current, measured in amps, is the rate at which charges flow. It is analogous to
the rate of flow of the water at the end of the hose.
Voltage, measured in volts, is the force required to make current flow. It is analogous to the
water pressure in the hose.
Resistance is a material’s tendency to resist the flow of charge. Think of the resistance
as the diameter of the hose. The smaller the hose, the higher the resistance.
So if you have two tanks with the same amount of water, but one has a smaller hose than
the other, or higher resistance, it will have a lower flow, given the same pressure.
Similarly, a circuit with higher resistance, at constant voltage, will have a lower current.
But, if water flow from the tank is constant, but the diameter is smaller, than pressure
will increase.
Similarly, if current is constant in a circuit, then a higher resistance will result in higher
voltage.
How does this water analogy relate to direct current and alternating current?
DC is similar to the normal flow of water through the hose that we are seeing here.
The water flows in one direction. In this scenario, current flows at a constant rate
over time: This was championed by Thomas Edison in the famous current wars that pit him against
Nikola Tesla, who championed AC.
AC is like the water flowing back and forth within the hose 50 or 60 times per second,
This is called the frequency and is designated as either 50 Hertz (50Hz) or 60 Hertz (60Hz),
and depends on the electric system of the country.
This is where the water analogy is not so great, because water doesn’t flow back and
forth in a hose. But alternating current does. Alternating current is easily created by industrial electric generators,
and is now the world standard for transmission
of electricity.
Why did this technology win out over DC, even though Thomas Edison, one of the most famous
and powerful men of the 19th century tried his best to disparage it.
The answer has to do with efficiency and power delivery. Power is like the volume or amount
of water coming out of the hose. The reason electricity is generated is to send power
to homes and factories.
The mathematical formula for power equals the current times voltage. The greater the
current and the greater the voltage in the transmission lines, the more power that is
available to be delivered.
Using the formula P = I*V, you can see that the same amount of power can be transmitted
either at high current and low voltage, or low current and high voltage. But one is better
than the other.
You see, the power cables used to transmit electricity have a certain amount of resistance
per meter of distance. The longer this cable is, the more resistance there is in the power
line.
And anytime you pass a current through resistance, you create heat, given by Joule’s equation
for electric heat, where heat is equal to current squared times the resistance.
Heat is wasted energy, because it essentially robs the grid of useful power that is not
delivered to homes and business, but is lost to the air. So it is crucial to minimize this
heat, otherwise much of the power that you want to deliver is going to get wasted.
Since I = P/V from our power equation, if we substitute that back into the heat equation.
We see that Heat equals Power squared times resistance R, divided by voltage V squared.
You can see now that in order to reduce heat, we want to MAXIMIZE voltage V to deliver the
same amount of power P,
because for any given power and resistance, the higher the voltage that we can create
in the circuit, the lower the heat loss we will have while transmitting electricity.
In modern electric power grids, electricity is routinely transmitted for hundreds of kilometers
at hundreds of thousands of volts.
But voltage can not be this high when it arrives at your home because it would be very dangerous,
and could easily electrocute you. So, it has to be stepped down before it gets to your
house. This is done via a transformer which steps down the voltage from hundreds of thousands
of volts to typically between 100 to 240 volts, which is the voltage of electrical outlets
in most homes around the world.
This stepping up and stepping down of voltage is where alternating current shines in comparison
to direct current.
Direct current cannot be easily transformed from low voltage to high voltage and visa
versa. But this is quite easy to do with alternating current. And here’s the reason why:
When alternating current passes through a coil, it produces a constantly changing magnetic
flux, per Maxwell’s equations, that say that changing electric fields create magnetic
fields. If we put a loop or ring of iron through the coil, it can concentrate the changing
magnetic flux to within the ring.
Now if we wind another coil around the other side of this ring, we can create electricity
and induce voltage within the new coil, because again according to Maxwell’s equations a
changing magnetic field creates a circulating electric field.
It so happens that the voltage we create in the second coil is proportional to the number
of loops or turns we place around the iron ring. Using this method we can create voltage
that is much higher in the second loop than the original voltage in the first loop.
This is very roughly how a transformer works, and this method is used to step up the voltage
for transmission over vast distances, to minimize energy loss.
And we can use this same method to step down the voltage to a safer level, before it is
delivered to your home, by simply making a smaller number of turns in the step down transformer.
But as you can see, transformers like this require a time-varying voltage to function.
And since direct current is constant, and only alternating current is time-varying,
transformers like these only work with AC electricity.
In Edison and Tesla’s time, there was no easy way to transform voltage with direct
current. And this is the primary reason Tesla’s AC won out over Edison’s DC in the early
era of electrical transmission.
You might ask, can devices work equally well with DC or AC current? Many devices—like
light bulbs—only require that the electrons move. They don't care if the electrons flow
through the wire or simply move back-and-forth. So a light bulb, for example, can typically
be used with either AC or DC electricity.
The fact that that alternating current powers most of the modern industrial world has made Tesla
the winner of the current wars.
But as in most wars, there are always two sides to the story. Was DC really a losing
concept long term? Not really. You have to remember that most high tech appliances today
that are powered batteries, like your laptop, cell phone, and iPad are all powered by direct
current.
In addition, in the late 20th century, engineers figured out a way to transmit electricity
using high voltage direct current, or HVDC. It turns out HVDC is more efficient than high
voltage AC for transmitting electricity over extremely large distances of 1000 km or more.
This is because smaller, cheaper lines can be used to transmit the same amount of power
using DC, and there is less induction loss because no changing magnetic field exists
with DC, unlike with AC. But the cost of DC transformers is huge, 10’s of million of
dollars vs. only thousands of dollars for AC transformers. So HVDC is only cost effective
for very long transmission lines.
Edison’s place in history as an inventor and electrician is secure. But in many ways
Tesla went even further. He envisioned fluorescent lights, technology of the radio, and remote
control. But he was an eccentric. Because along with these genius ideas, he also
spoke about crazy things like splitting the earth in half, and creating a death ray that
could destroy thousands of airplanes at the same time.
Scientists didn’t know what to believe in his time, and were slow to praise him. Tesla
he did not get his due acclaim until after his death. But I don’t think anyone disputes
today that he was one of the most forward thinking, and dynamic visionaries that ever
lived.
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that Edison and Tesla had leading to the battle of the currents.
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And if you have a question, leave it in the comments section because I try to answer all of them.
I will see you in the next video my friend!