W3_L3_Motor and Generator

Summary

In 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

00:00

🌡 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.

05:09

🔌 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.

10:09

💡 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.

Keywords

💡Sine Wave

A sine wave is a continuous smooth oscillation that occurs in a periodic motion, typically represented graphically as a wave with a smooth 'peak-and-trough' shape. In the video, the sine wave is discussed in the context of power supply lines, where a 50 hertz sinusoid is mentioned, indicating the frequency of the alternating current in the power grid, which is a fundamental concept in understanding electrical engineering.

💡Hertz

Hertz (Hz) is the unit of measurement for frequency, representing the number of cycles per second of a periodic phenomenon. The script refers to '50 hertz' to describe the frequency of the sine wave in the power supply, which means that the wave completes 50 cycles every second, a key parameter in electrical systems.

💡DC (Direct Current)

Direct Current (DC) is an electric current that flows in a constant direction, typically from the negative terminal of a power source to the positive. In the video, DC is used to power a fan, and the concept is explored in terms of how it creates a fixed magnetic field and results in the rotation of the fan's motor.

💡AC (Alternating Current)

Alternating Current (AC) is an electric current whose direction and magnitude vary periodically with time. The video demonstrates how manual rotation of a fan can generate an AC signal, showing the oscillations on an oscilloscope, which contrasts with the DC current used to power the fan initially.

💡Wattage

Wattage is a measure of power, or the rate at which energy is used or generated, and is calculated by multiplying voltage by current. The script mentions calculating wattage to understand the energy consumption of the fan, which is a basic principle in electrical engineering and everyday appliance usage.

💡Voltage

Voltage, also known as electric potential difference, is the force that pushes electric charge through a conductor. The video script discusses measuring voltage with a voltmeter and mentions a 'jump' in voltage when the fan is manually rotated, indicating a change in electric potential.

💡Oscilloscope

An oscilloscope is a device used to display and analyze the waveform of electronic signals, allowing one to observe changes over time. In the script, an oscilloscope is used to observe the time-varying signal generated when the fan is manually rotated, providing visual evidence of the AC signal produced.

💡Magnetic Field

A magnetic field is a region around a magnetic material or a moving electric charge within which the force of magnetism acts. The video explains how a fixed magnetic field interacts with a rotating coil in an electric motor, creating a force that results in the motor's rotation.

💡Torque

Torque is the force that can cause an object to rotate about an axis. In the context of the video, torque is generated by the interaction between the current flowing through the fan's coil and the fixed magnetic field, leading to the rotation of the fan.

💡Faraday's Law

Faraday's Law of electromagnetic induction states that a change in magnetic flux through a circuit will induce an electromotive force (EMF). The video script uses Faraday's Law to explain how the manual rotation of the fan's coil in a magnetic field generates an AC voltage, illustrating the principle behind electricity generation.

💡Energy Transformation

Energy transformation refers to the process of converting energy from one form to another without creating or destroying energy. The video emphasizes that when the fan is manually rotated and generates voltage, it's an example of energy transformation, where mechanical energy is converted into electrical energy, debunking the idea of a perpetual motion machine.

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]