W3_L3_Motor and Generator
Summary
TLDRIn this educational video, the presenter explores the physics behind a fan's motor, explaining how a direct current (DC) produces rotation. They then conduct an experiment to manually rotate the fan and use an oscilloscope to observe the resulting alternating current (AC) signal. The video highlights the fundamental principles of magnetism and Faraday's law, demonstrating how mechanical energy is converted into electrical energy, debunking the myth of perpetual motion and emphasizing the importance of energy transformation in electrical engineering.
Takeaways
- 🌡 The script begins with a discussion about the hot weather in Chennai, India, setting an informal tone for the conversation.
- 🔌 The origin of the 50-hertz sine wave in power supply lines is introduced as the main topic for discussion, highlighting the significance of sinusoids in electrical engineering.
- 🔍 The fan's electrical specifications are examined, including its DC 12-volt and 0.18-ampere rating, leading to a calculation of its wattage and energy consumption.
- 🛠 An experiment is conducted to connect the fan to a 12-volt DC supply, demonstrating the fan's operation and the principles of electromagnetism within its motor.
- 🔧 The script describes the process of manually rotating the fan to generate a signal, illustrating the conversion of mechanical energy into electrical energy.
- 📊 The oscilloscope is used to observe the time-varying signal produced by manually rotating the fan, revealing an alternating current superimposed on a DC value.
- 🧲 The principles of magnetism are explained to understand the oscillations observed on the oscilloscope, relating to the coil's interaction with a fixed magnetic field.
- 🔄 The script discusses Faraday's law of electromagnetic induction, explaining how a changing magnetic flux through a coil generates an electromagnetic force (EMF), resulting in an AC signal.
- 🔌 The connection between the principles demonstrated with the fan and the broader context of AC power generation, such as in hydroelectric power plants, is made.
- 🛑 The script emphasizes the impossibility of perpetual motion machines and the conservation of energy, highlighting the transformation of energy from one form to another.
- 📚 The closing remarks promise a deeper exploration of sine wave properties in future lectures, linking them to previous experiments.
Q & A
What is the purpose of the fan in the video script?
-The fan in the script is used as a practical example to demonstrate the principles of electrical engineering, particularly the generation of a sine wave when a motor is operated.
What is the specification of the fan mentioned in the script?
-The fan has a specification of DC 12 volts and 0.18 ampere, which can be used to calculate its wattage and the energy it consumes.
How is the wattage of the fan calculated?
-The wattage of the fan is calculated by multiplying the voltage (12 volts) with the current (0.18 ampere), as per the formula Power = Voltage x Current.
Why does the fan not work the first time it is connected to the power supply?
-The script humorously suggests that with most electronic gadgets, things don't work the first time, implying that troubleshooting or adjustments may be necessary.
What happens when the fan is manually rotated after being disconnected from the power supply?
-When the fan is manually rotated, it generates a time-varying signal, which is observed on the oscilloscope as a jump in voltage followed by oscillations around a DC value.
What is the basic principle behind the rotation of the fan when connected to a DC current?
-The rotation is due to the interaction between a fixed magnetic field and a coil with a DC current flowing through it, which creates a torque that causes the fan to rotate.
What experiment is conducted by reversing the process of the fan?
-The experiment involves manually rotating the fan to generate a signal, which is then observed on an oscilloscope to understand the changes in voltage when the fan is not powered by an external source.
Why do the oscillations appear when the fan is manually rotated?
-The oscillations are due to the changing magnetic flux through the coil as it rotates in the fixed magnetic field, which according to Faraday's law of electromagnetic induction, generates an alternating voltage.
How is the AC component of the power supply generated according to the script?
-The AC component is generated by the rotation of a coil in a magnetic field, which changes the magnetic flux through the coil, leading to the generation of an alternating current.
What is the significance of the sine wave in electrical engineering as mentioned in the script?
-The sine wave is fundamental to electrical engineering because it represents the basic form of alternating current used in power supplies, which is generated through the principles demonstrated in the script.
Why is it incorrect to think that energy can be generated out of nowhere in the experiment?
-It is incorrect because energy cannot be created or destroyed; it can only be transformed from one form to another. In the experiment, the manual work done to rotate the fan is converted into electrical energy, with losses due to inefficiencies.
Outlines
🌡 Understanding the Origin of the Sine Wave
In the first paragraph, the discussion revolves around the origin of the sine wave in power supply lines, specifically the 50 hertz sinusoid. The host, Bobby, is introduced to the concept of calculating the wattage of a fan, which is connected to a 12-volt DC supply. The fan's operation is explained through the interaction of a fixed magnetic field and a coil carrying a DC current, resulting in torque and rotation. The paragraph concludes with an experiment to manually rotate the fan and observe the resulting electrical signal, which is expected to be time-varying and not a constant DC signal.
🔌 Generating AC Signal by Manually Rotating the Fan
The second paragraph delves into the experiment of manually rotating the fan to generate a signal, which is then observed on an oscilloscope. The initial expectation is not to see a DC signal, and indeed, the oscilloscope captures a voltage jump and oscillations, indicating the presence of an alternating current superimposed over a DC value. The explanation involves basic magnetism, where a rotating coil in a magnetic field induces an electromotive force (EMF) according to Faraday's law of electromagnetic induction. The paragraph explains the relationship between the manual rotation of the fan, the changing magnetic flux, and the resulting AC voltage, highlighting the fundamental principles of electrical engineering.
💡 The Fundamentals of AC Power Generation and Energy Transformation
The final paragraph addresses the broader context of AC power generation, mentioning hydroelectric power as an example. It explains that the power supply at home is AC because it is generated by rotating turbines in power plants. The paragraph also dispels the myth of perpetual motion machines, emphasizing the conservation of energy and the transformation of energy from one form to another. The experiment conducted by Bobby, where manual work is used to rotate the fan and generate voltage, illustrates the principle of energy conversion with significant losses. The paragraph concludes with a teaser for the next lecture, which will explore the properties of sine waves and their relevance to previous experiments.
Mindmap
Keywords
💡Sine Wave
💡Hertz
💡DC (Direct Current)
💡AC (Alternating Current)
💡Wattage
💡Voltage
💡Oscilloscope
💡Magnetic Field
💡Torque
💡Faraday's Law
💡Energy Transformation
Highlights
Discussion about the origin of the 50 hertz sinusoid in power supply lines.
Calculating wattage by multiplying voltage with current.
Demonstration of connecting a 12-volt DC fan to a power supply.
Explanation of the motor's internal workings involving a fixed magnetic field and a coil.
Experiment to manually rotate the fan and generate a signal.
Observation of a time-varying signal when manually rotating the fan.
Understanding the jump in voltage and oscillation during the manual rotation experiment.
Basic principles of magnetism explaining the oscillations in the manual rotation experiment.
Faraday's law of electromagnetic induction applied to the fan rotation experiment.
The relationship between direct current (DC) and alternating current (AC) in the context of a motor.
Explanation of energy transformation from mechanical to electrical during the fan rotation.
Clarification that energy cannot be created or destroyed, only transformed.
Discussion on the practical implications of energy loss during the fan rotation experiment.
Introduction to the properties of sine waves and their importance in electrical engineering.
Linking the experiment's findings to previous experiments and their significance.
Upcoming lecture on the properties of sine waves.
The importance of understanding the fundamental role of sinusoids in electrical power generation.
Transcripts
foreign
[Music]
hi Bobby
I know Chennai is
weather is very hot today
but is that the reason you bought a fine
no no I don't think this fan is going to
help you one bit to overcome the
sweltering heat of Chennai but I thought
we should discuss about the origin of
the sine wave you know last time you
mentioned that in in our power supply
lines we get 50 hertz sinusoid correct
so I think we should just discuss why we
are getting it you know what is the
origin and reason for that so what you
see here right can you read the
specification of this yeah DC 12 volt
0.18 ampere yeah so I mean you can
easily calculate the wattage by the way
from you know what we did earlier
multiply the volt with current you will
get the wattage and how much energy this
fan is going to consume right yes so can
you connect this to a 12 volt DC Supply
and show me yeah you know what happens
so I see power supply here yeah this is
12 volt yes
letting now we can stop measuring with
the voltmeter we have already measured
this already earlier
and
not surprisingly with most electronic
gadgets things don't work
the first time
what happened is this not on no this is
all I can
imagine right so just get the wire
straightened out and
yeah yeah so what happens oh the span is
working so the fan is working right so
when you apply a voltage right across
this fan
12 volt and provide the necessary
current this fan is rotating very nicely
right so essentially what is happening
inside this fan is you have a fixed
magnetic field okay B
and uh in this you have a coil
I've just drawn it as a square coil here
but otherwise you have you know some
other coils also and you have a current
I that is flowing through this coil this
current I is a DC current
yeah and this was about 0.18
amps right and so what is going to
happen is you're going to have a force
bil right which is going to be up you
know equal and opposite
on these two sides but on this side it's
going to form a couple
right you're going to have a torque so
all the forces balance each other and
this coil cannot move but it is going to
rotate you will have a coil I mean
you'll have a bil into the uh you know
into this distance here which is going
to give you a torque right and that is
essentially going to lead to the
rotation of this okay okay so there will
be a spindle or something to hold this
exactly so it's a more complicated thing
as how you allow it to rotate and pass
current and all that's a different
that's how a motor is you know designed
very carefully but let's not get carried
away with this and over a basic idea
about it basic idea of so but the main
point I'm trying to highlight here is we
are passing a direct current and we are
causing rotation yeah now I want you to
try an interesting experiment
reverse this process I want you to
rotate the fan and generate some signal
manually and let's see what happens okay
so as usual you know we are not going to
look at a state you know a DC signal
right we are not going to expect a DC
signal it's going to be time varying so
let's you know so you mean I'll just use
my hand and rotate yeah can you just
rotate and see what happens something
like this yeah something like that so
it's not a constant speed yeah it will
be a speed that will be reducing already
exactly you're you're rotating it and it
will slow down and come down to zero
okay so you are okay with that I'm okay
with that because it's a again we are
trying to do a first order experiment to
understand what's happening okay so I
want you to kind to connect this battery
oscilloscope sure because it's a Time
varying signal now okay and then I want
to observe what is going to happen let's
see whether this will generate something
first yeah exactly
okay
yeah right so what you see is
yeah so evidently there is a jump
in this voltage
so you rotate it
once more
yeah okay so this is what we are going
to see now so what we did was we just
took the fan we connected nothing to it
there's no power supply connected to it
we just collected the output of you know
those two terminals through which we fed
the DC current to the oscilloscope we
rotated it and saw what happened right
so what we got in that process was the
following okay we got a voltage because
the oscilloscope is now measuring a
voltage right it was sitting at some
point five volt and at some point you
rotated it and you started it very fast
yeah so there was a huge jump and then
there was an oscillation like this and
ultimately it came back to its
steady state right so this is when you
started
and this is when it stopped
foreign
because what we did earlier was we
passed a DC current and we got a
rotation yeah now
we are doing some manual you know
rotation of the fan but we are getting
not just a DC voltage we are getting
some oscillations around it so there is
an alternating current
super post over some DC value okay so
it's not going to be easy to analyze
exactly what happens here but at least
why we get this oscillations is
something that we can explain through
basic uh magnetism
okay so I will just go back here and
okay so what we have now right is we are
again
placing a coil like this
okay and we have a fixed magnetic field
passing through this coil
okay this is B
and for now let's just consider a square
coil which length L and L I'm not going
going to make it a rectangle or whatever
this area Vector is going to point
perpendicular to the surface
magnetically now the magnetic field is
in a fixed Direction but the area Vector
is going to be perpendicular to this
coil yes okay okay so this area Vector
is going to be perpendicular to the
surface of that coil and the magnetic
field is going to point like this so you
look at this this is my a
Vector this is my B vector and this
Theta
is going to be so let's assume that this
coil is spinning at a constant angular
velocity of
Omega naught t
that means this angle that it forms
between b and a is going to be a
function of T and it is going to be
Omega naughty now this is the case if it
were a constant angular velocity in this
case of course we started with something
it slowed down because of friction and
all that and we are not able to sustain
that angular velocity so the
Omega naught itself is a function of
time so there will be an angular
deceleration that we have to consider
let's not worry about that for now so
what happens is the magnetic flux
to this coil is going to be integral
B dot t a
right and this the magnitude is constant
okay it is B the area is also constant
the the value is constant but the vector
angle keeps changing so this will be COS
of
Omega naught t
so what you now see is a fixed coil
which is rotating in a magnetic field
and the magnetic flux is changing with
time and Faraday's law of course tells
you that this is going to you know
generate an electromagnetic force right
an EMF right EMF equal to some voltage
which is minus D Phi by
DT
right so this essentially if you just
solve you will get B A into Omega naught
sine of
Omega naught
okay right so
this is the this is the beauty in the
motor we passed current a direct current
the bil that force is what led to a
torque and it was able to generate but
the AC component was the fact that that
was now rotating at an angular velocity
Omega naught now what we are doing is we
are rotating this from outside at an
angular velocity Omega naught and that
is leading to an AC current
right it's not just a DC generation and
that is why even the uh power supply at
home and all that is AC because the
generation itself you know hydroelectric
power gets generated in this manner
right you have reverse flowing over a
turbine that rotates and that generates
some electricity and that is you know
now distributed to the country right and
uh that's why you have uh you know
sinusoids are very fundamental to
electrical engineering right this is
just one of the aspects but let me ask
you one question yeah did you generate
energy out of nowhere magically no I was
providing energy exactly so this is
another very important aspect for
electrical engineers
sometimes you might think there is a
possibility of a Perpetual machine
somewhere that will not happen energy
has to be generated from you know has to
be put in from somewhere and it'll get
transformed to something else so here
Bobby you know did all the work with his
hand and got the fan rotating and that
generated some small voltage you know
there's a huge loss by the way the
amount of work that he did and the
amount of energy we got out is not even
comparable because it's a huge loss
there but the key point is energy was
not generated it was actually just
transformed from one form to another
converted was just converted from one
form to electrical energy in this case
and the maximum voltage is decided by
yes the maximum voltage therefore will
be decided by this right so this will be
the amplitude VP sine Omega naught
t
so in the next lecture
we will actually look at the properties
of these you know sine waves and you
know link it to earlier experiments that
we did as well
thank you thank you
foreign
[Music]
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