Have you ever wondered how the electricity that you use in your home is generated?
Probably you have heard that it is generated in a damp,
with a wind generator, or even in a nuclear plant
and that is correct, but it doesn't fully answer our question.
If you are thinking that each of these machines convert movement into electricity,
we are closer to the truth,< but its operation remains as a mystery.
In the previous video we saw how an electric charge in motion can generate a magnetic field,
also that two bodies with a magnetic field interact with each other
being able to generate movement as in electric motors
and basically the way in which electricity is generated is reversing this process.
After Hans Christian Oersted discovered that an electric current can generate a magnetic field
the question that arose is - could a magnetic field generate an electric current?
The person who discovered the answer to this question was Michael Faraday
Since while testing with magnets he noticed a strange behavior.
When a magnet passed through the inside of a copper coil,
a voltage difference was generated at the ends of the cable.
But with the peculiarity that this will only happen when the magnet was in motion.
And that, in addition, the sign of the voltage varied
depending on the direction in which the magnet moved.
In fact, with very simple materials we can verify that this happens.
We just need a multimeter, a cable and a magnet
And we can find demonstrations like this very easily on the Internet
"You see a deflection to the right, pull it out to the left
and if I go in quickly you see a much greater deflection."
With his experiments, Michael Faraday ended up defining the law of induction
which tells us that the electro-motive force generated
is equal to the derivative of the magnetic field with respect to time.
And what does this mean in simple words? Let's review calmly.
First. the electro-motive force, although it has its own definition
it is equivalent to the voltage that will be generated in the circuit
the magnetic field flow refers to the direction and force of the magnetic field
and finally the derivative with respect to time could be translated simply as a variation in time.
And at this point some of you must be thinking: what happens with that negative sign?
Well, Heinrich Lenz discovered that the polarity of the electro-motive force is such
that it generates a current whose magnetic field opposes the change that generates it.
Its behavior can be appreciated in this experiment.
It's just a magnet falling into a copper tube but it still looks like it breaks the law of gravity
and that's because the magnetic field of the magnet itself is generating a current
which generates a magnetic field that opposes its movement.
But I think we're getting far from the subject.
Going back to our initial experiment, what happens if we have a coil connected to a voltmeter
and we leave this magnet in a static position for three seconds?
Exactly, nothing happens,
because the formula told us that there should be a variation of the flow of the magnetic field over time,
and since the magnet was always in the same place there was no variation.
Let's try again.
What happens this time if we bring the magnet closer during the three seconds?
A voltage difference is generated.
What if we do it to the other side?
I think you already understood, but look what happens if we repeat the cycle.
What is happening is that an alternating current is being generated
Every time we are closer to understanding how the black box that we saw at the beginning works.
So let's see how we compare what we have so far with the generators used today.
The wind generator rotates because the air collides with its blades
and generates a torque with respect to the shaft, which generates energy.
The hydroelectric plants allow water that is in height to fall on turbines
forcing them to turn and generate energy.
And nuclear power plants produce a large amount of heat
that is used to heat water which when evaporated expands its size
and being guided by the pipes.
Guess what? It spins a turbine.
Sure you have already noticed, but our generator uses a linear movement
and the other generators have a circular motion.
And we could implement a mechanical system to convert circular motion into linear and generate energy,
but that's not how exactly they work.
By adding more pieces we increase the complexity of the system
and therefore we increase the chances of it failing.
But perhaps most important is that in each contact between two pieces will be generated a friction
which is going to make us waste the energy that we are trying so hard to obtain.
So the ideal would be to directly convert circular motion into electrical energy.
Remember Peter Barlow's engine?
Faraday made his own suspiciously similar generator
which when turning a copper disk through the middle of a magnet generates a direct current.
In this particular case it is the conductive material that is moving
and not the magnetic field
but the formula is still true, since in reality how the movement is measured
will depend on what is being used as a reference.
Now let's take a magnet spinning on an axis and put a conductive material around it.
Since during the half of the trip the magnets are approaching one of the cables
and during the other half they are moving away,
the magnetic flux variation is reversed, and therefore an alternating current will be generated.
But if we also exchange the magnets by the wire
and add a switch to change the connection of the cables,
that is, basically we use a DC motor. then we will generate direct current.
There are multiple configurations with more or less magnetic poles
or with a different arrangement of the cables, but they all work on the same principle: Faraday's law.