Lesson 1 - What Is Alternating Current? (AC Circuit Analysis)
Summary
TLDRIn this AC circuit analysis tutorial, host Jason introduces the concept of Alternating Current (AC), emphasizing its ubiquity in household appliances. He explains that unlike Direct Current (DC), AC's voltage and current constantly change direction, flipping 60 times per second in the US. Jason stresses the importance of understanding trigonometry and sinusoidal functions to analyze AC circuits, promising a clear explanation of complex terms like frequency and phase angle in upcoming lessons.
Takeaways
- đ The lesson is an introduction to AC (Alternating Current) circuit analysis, presented by Jason, the tutor.
- đ AC is fundamentally different from DC (Direct Current) as it involves changing voltage and current directions, unlike the constant flow in DC circuits.
- đ The term 'sinusoid' refers to the wave shape of sine and cosine functions, which are crucial in understanding AC behavior.
- đšâđ« Jason emphasizes the importance of prior knowledge of voltage, current, resistance, capacitors, inductors, and circuit analysis techniques for understanding AC circuits.
- đ AC is used in power grids due to its efficiency in long-distance transmission, and is the standard for most home and industrial electrical systems.
- âïž Generators produce AC through the rotation of a coil within a magnetic field, resulting in a cyclic recurring voltage.
- đ In the United States, the standard frequency for AC is 60 Hz, meaning the voltage and current switch directions 60 times per second.
- đ Different countries may have different frequencies for their AC power systems, but the concept of alternating remains the same.
- đ The voltage and current in AC circuits are represented graphically as sinusoids, which are mathematical functions that describe their periodic nature.
- đ A fundamental understanding of trigonometry is necessary for analyzing AC circuits, as it helps in understanding the sine and cosine wave patterns.
- đ The next steps in the course will involve writing down mathematical functions for voltage and current in AC circuits and understanding terms like frequency and phase angle.
Q & A
What is the primary focus of the AC circuit analysis tutor lessons?
-The primary focus of the AC circuit analysis tutor lessons is to teach the principles and skills needed to analyze and understand alternating current circuits.
Why is it important to have a strong foundation in DC circuit analysis before studying AC circuits?
-It is important to have a strong foundation in DC circuit analysis because the techniques learned, such as Ohm's law, node voltage, and Norton equivalent circuits, are directly applicable to AC circuits once the theory behind alternating current is understood.
What is the significance of the term 'phasor' mentioned in the script?
-The term 'phasor' refers to a concept that will be introduced later in the lessons, which is essential for understanding and analyzing AC circuits, particularly in terms of how voltages and currents behave over time in relation to each other.
Why is trigonometry important for understanding AC circuits?
-Trigonometry is important for understanding AC circuits because the voltage and current waveforms in AC circuits are sinusoidal, and knowledge of sine and cosine functions is necessary to analyze and represent these waveforms mathematically.
What is the difference between direct current (DC) and alternating current (AC)?
-Direct current (DC) is characterized by a constant flow of electric charge in one direction, while alternating current (AC) involves a periodic reversal of the direction of the electric charge flow, typically 60 times per second in the United States.
Why is AC more efficient for transmitting electricity over long distances?
-AC is more efficient for transmitting electricity over long distances because it can be easily transformed to higher or lower voltages using transformers, which reduces power loss during transmission and allows for more efficient use of the power grid.
What is the frequency of the AC voltage in the United States, and how does it relate to the concept of sinusoids?
-The frequency of the AC voltage in the United States is 60 hertz, which means it switches direction 60 times per second. This rapid switching is represented by sinusoidal waveforms, which are the graphical representation of sine and cosine functions.
What does the term 'sinusoid' refer to in the context of AC circuits?
-In the context of AC circuits, the term 'sinusoid' refers to the wave-like pattern of voltage and current that changes periodically, which is the same shape as that of sine and cosine functions in trigonometry.
Why is it necessary to review trigonometry before diving into AC circuit analysis?
-It is necessary to review trigonometry before diving into AC circuit analysis because understanding the characteristics of sine and cosine functions is crucial for analyzing the behavior of voltage and current in AC circuits, which are represented by sinusoidal waveforms.
What is the significance of the wall socket example used in the script to explain AC?
-The wall socket example is used to illustrate the concept of AC by showing how the voltage between the prongs of a wall socket alternates direction, representing the alternating nature of AC and how it differs from the constant voltage of a DC source.
Outlines
đ Introduction to AC Circuit Analysis
In this introductory lesson, Jason, the host, expresses excitement about teaching AC (alternating current) circuit analysis, emphasizing that the skills learned in previous lessons are crucial for understanding AC. He mentions that all techniques such as Ohm's law, node voltage, and Norton equivalent circuits will be applicable to AC circuits once the basic theory of AC and the use of phasors are understood. Jason also stresses the importance of reviewing trigonometry, especially sine and cosine functions, as they are fundamental to grasping AC concepts. He introduces the term 'sinusoid' as interchangeable with AC, highlighting its efficiency in long-distance transmission and its generation through the rotation of coils in magnetic fields.
đ Characteristics of Alternating Current
This paragraph delves into the characteristics of AC, explaining how it differs from DC (direct current) by constantly changing direction, which is visualized through the alternating voltage in a wall socket. Jason instructs viewers to observe a wall socket to understand this concept. He explains the frequency of AC in the United States, which is 60 Hz, meaning the voltage direction changes 60 times per second. This rapid flipping is a key feature of AC, which is used in most household appliances that plug into a wall. The paragraph also contrasts AC with DC, where the current flows in one direction, whereas in AC, the current switches direction in sync with the voltage changes.
đ Understanding Sinusoidal Functions in AC
The final paragraph provides a basic overview of sinusoidal functions, which are the graphical representation of AC voltages and currents. Jason describes how these sinusoids, or sine waves, are fundamental to AC circuits, alternating 60 times per second in the US. He prepares learners for the next section, where mathematical expressions for these sinusoids will be introduced, including concepts like frequency and phase angle. The paragraph ends with an encouragement to review trigonometry to ensure a solid foundation before proceeding with AC circuit analysis.
Mindmap
Keywords
đĄAlternating Current (AC)
đĄCircuit Analysis
đĄSinusoid
đĄTrigonometry
đĄOhm's Law
đĄ
đĄFrequency
đĄPhase Angle
đĄVoltage
đĄCurrent
đĄResistors, Capacitors, and Inductors
đĄThevenin and Norton Equivalent Circuits
Highlights
Introduction to AC circuit analysis by Jason, the tutor, emphasizing the culmination of previous circuit analysis skills.
Brief review of what alternating current (AC) is and its graphical representation.
Importance of understanding the skills learned in previous lessons for AC analysis.
Relevance of Ohm's law, node voltage, and Norton equivalent circuits to AC circuits.
The necessity of understanding the theory behind AC and the use of phasors.
Request for students to review prior circuit analysis material for a solid foundation in AC analysis.
Recommendation to refresh trigonometry knowledge, especially sine and cosine functions, for AC analysis.
Explanation of the term 'sinusoid' and its interchangeability with AC in certain contexts.
The historical and practical reasons behind the use of AC, including its efficiency in long-distance transmission.
Description of how generators produce alternating currents through the rotation of coils in a magnetic field.
The prevalence of AC in household appliances and its distinction from DC sources.
Clarification of the sinusoidal wave nature of AC and its characteristics.
Visualization of voltage alternating between two prongs of a wall socket in an AC circuit.
The frequency of AC in the United States, mentioned as 60 Hertz, and its rapid switching of voltage directions.
Difference between DC and AC in terms of current direction and voltage stability.
The sinusoidal nature of voltage and current in AC circuits, visualized as sine or cosine waves.
Assurance that understanding of AC and its mathematical representation is not difficult and will be clearly explained.
Encouragement for students to review trigonometry before proceeding with AC circuit analysis.
Preview of the next lesson's focus on writing sinusoidal functions for voltage and current in AC circuits.
Transcripts
hello welcome to this lesson of the AC
circuit analysis tutor I'm Jason I'll be
your host with this uh set of lessons
with this course here and I'm very
excited to teach uh alternating current
AC analysis to you because I've been
building the skills with you uh as we've
been working on our circuit analysis
skills up till now and everything we've
been doing all of the things that we
have learned up until this point really
is culminating in us being able to
tackle AC analysis so what we're going
to do in this lesson is just kind of
briefly review what is alternating
current what is AC uh kind of give you a
little bit of a graphical outline as to
what it exactly it is I think you'll
probably learn a few things even if you
kind of know a little bit about AC
already uh and then what I really want
you to to know though as we go through
this class here is that the skills that
we have learned up until this
point just think back to everything
we've learned we've learned about
voltage current resistance learned about
capacitors and inductors we've learned
about uh the current voltage
relationships OHS law node voltage thin
and Norton all of that stuff that we've
done it's all extremely crucial uh and
I'll give you a little bit of a preview
the reason why all that stuff's so
important is because really for AC
analysis once I show you how to set
everything up all of those techniques
that we have learned before are going to
be directly applicable to all AC
circuits and I'll say that again because
it's really important all of those
techniques we've learned before th and
Norton equivalent circuits series and
parallel Arrangements node volt all the
stuff that we've done the techniques of
analysis they're all applicable to
alternating current circuits but you
have to know a little bit of theory
behind alternating current um and how to
use what we're going to call phasers
which will be a little bit later you
have to know how to use all that stuff
and be very comfortable with it so I
don't want to just bulldoze into it I
want to make sure you understand what AC
is I want to make sure you understand a
little bit later how we're going to
handle these uh these sources and all
the capacitors and everything in a an
alternate current so that whenever we do
the problems using Fant or
Norton or node voltage or mesh current
or whatever you'll be very comfortable
with the new material the AC part and
you all already should be pretty
comfortable with the pr prior material
so if you haven't already done so I
strongly encourage in fact I require you
to go back and learn
everything that I've taught in circuit
analysis up until this point uh and the
second thing that I want to request of
you I'm going to give you a good primer
on on trig function here but if you're
Rusty in s and cosine what they look
like characteristics you know basic
ideas that you learn in trigonometry I
strongly recommend that you go and
review some trigonometry if you're Rusty
in that I'm going to go through it with
you of course like I always do but I
really want to make sure that when you
come into this and I talk about sign and
cosine you at least kind of know what
they look like I'm going to draw it for
you but you know you still there's a lot
of mathematical background that we get
that's going to be useful in this
class so we're going to we're going to
throw around some big terms in this
class first one we've already
encountered alternating current we're
also going to throw around uh a term
called sinusoid all right so those are
kind of interchangeable basically uh if
you could if I could boil it down for
you alternating current is exactly what
it sounds like you see when you compare
that to what we've done before which was
direct current and direct current
circuits which we already covered
everything is is basically constant you
have a battery uh or some other fixed
voltage source or current Source it
doesn't change when you switch the
circuit on you might have some transient
stuff but once it all settles out the
currents and the voltages all across the
components in a DC circuit they never
really change it's like a battery
operated toy or something and so as long
as the thing is supplying power you can
measure all over the circuit the
different currents and the voltages and
everything is staying the same nothing
is changing but in alternating current
it's fundamentally different all right
in alternating current current the
current or the voltage and I'll we'll
talk a little bit more about how to know
later but basically everything in the
circuit is going to be constantly
alternating or changing changing
directions literally it's going to be
actually changing directions and you
might say well why is there alternating
current why do we use alternating
current there's a lot of history between
DC and AC and it turns out that AC is
very very efficient for transmitting
over long distances so that's where we
have our whole power grid set up as
alternating current and when you go dig
back into physics you'll
realize that uh when you generate
electricity usually what you're doing is
you have a generator which is just a
coil of wire and some magnets and you're
rotating the coil of wire uh around the
mag around the magnetic field and that's
generating an electric current and
you'll see when you cut apart a motor
and see how they're actually constructed
the way they're built is they generate
these alternating currents because of
the rotation you go half a circle and
then you'll come back the other half the
circle and you go half the circle the
other half the circle so that's why it
leads to these cyclic recurring back and
forth kinds of voltages that are
generated and that's why you know we end
up using alternating current so much so
almost everything that you uh use at
home that's bigger than battery operated
device is going to deal with alternating
current anything that you plug into a
wall outlet is using alternating current
so think about your televisions think
about your refrigerators think about
your um you know stereo systems anything
that plugs into a wall is using
alternating current so when I say
alternating current I'm going to explain
what that is in a minute on the board um
but I'm going to throw in um another
term here called a sinusoid see I've
talked about s functions you know just
briefly you should learn those in trig
I'll talk about cosine functions when
you talk about sinusoid as a as a word
it just means that shape you know that
shape of a sign or a cosine in fact if
you remember back from rig s and cosine
have the same shape they have exactly
the same shape if you shift them over
and line them up they're the same thing
so I'll explain the differences here in
a minute between s and cosine as a
review but the shape is what we're
talking about so that up and down wave
nature that's called a sinusoid so
sometimes you'll hear me talk about
sinusoidal functions or your book you
might hear about that sinusoid over
there that just means that nice shape it
turns out that sin swords signs and
cosines they're extremely important in
all of engineering and science
um they pop up everywhere and sinus
swords are very very special and they're
they're so very common we use them all
the time because of that so let's talk
about some characteristics of sinusoids
or AC alternating current number one it
comes out of our wall and what do I mean
by that exactly I want you to visualize
this a little bit so imagine a wall
socket right so let's just go over here
let's go over here for now let's say we
have a wall socket usually you have a
plate like this and you have you know
one or two plugs there so usually you
have uh two guys like that with one of
this dots down there and you might have
something that looks kind of like this
so this is a a plug right don't worry
about the uh prong down here just kind
of forget about that for a minute so
I'll erase it even though you may have
that in your wall focus on the two uh
flat ones up here what's happening in
your wall socket okay what I actually
kind of want you to do while you're
watching this video is find a wall
socket in the room and look at it
nothing's plugged into it find one that
doesn't have anything plugged into just
kind of look at it and just listen to me
while we talk before your very eyes if
you look at these holes here if you had
invisible Vision if you had some kind of
vision that could
visualize um uh voltage without a meter
if you could see it then you would see
the voltage between these two prongs
alternating and switching Direction in
other words you know how we used to talk
about the voltage source right we have
to label it so in one instance of time
um
this prong has a plus and a minus right
that would be the voltage drop going
from there to there right but then if
you could watch it a short time later it
will flip around so that this one is
negative and this one is positive see
how they've alternated right so
literally it's plus minus and then it's
plus minus the other way so they flipped
around so this would be like your
voltage and if you had some kind of a
meter you could don't do this unless you
know what you're doing but you could
measure the voltage in the wall and you
would see that it literally switches
Direction how fast does it switch
directions well in the United States
it's 50 60 hertz right that's 60 times
per second now around the world there
are different frequencies of the
switching going on but in the United
States it's 60 htz 60 times per second
so it's very fast me think about 60
times of anything per second
that's that's pretty fast so the
flipping around here is literally
flipping around just really really
really fast 60 times every single second
um but that's what's going on the reason
that 60 HZ goes into into the history of
of of the of the um you know of the
transmission and and generation system
that we have here different frequencies
around the world they have their own
standards but the idea is it's flipping
back and forth now in a DC circuit right
remember our good old DC circuits that
we we used to talk about a lot simple
ones like this if this is a DC Source
then we say that the
current is basically always going One
Direction it comes out of the positive
terminal back around forms a circuit
comes back to the other side now if it's
an
AC uh guy so you'll see this drawn
different ways but uh you might see a
little sine wave inside of there may not
always say that but um a lot of books
will will'll show it like that what this
means is that the voltage across this
guy sometimes as I've said before it's
plus minus but 60 * a second it flips
back where it's minus plus and because
it flips back and forth like that that
means sometimes the current is literally
flowing through the circuit this way but
then other times the circuit switches
direction or the current switches
Direction and goes back through the
source the other way and then it flips
back and goes the other way and then it
goes the other way and then it goes the
other way so literally the current in an
alternating current circuit that's why
it says alternating current right the
voltage is switching directions and also
in in in line with that the current is
switching directions so again look at
that wall socket you can visualize that
wall socket uh pretend that you've
plugged a vacuum cleaner or something
into it in one instance of time the
current may be coming out of the plug
into your load and back in to the other
prong but then just a short time later
you know a few milliseconds later
everything's flipped around and then
you've got the current coming out of the
right hand prong going this way and then
it flips around and it goes like this so
literally the current is coming out to
in out to in out to in N Out to n and
that's flipping back and forth 60 times
per second in the United States very
slight different variations around the
world that is the basic idea of what the
heck alternating current really is it
literally is changing 60 times per
second right back and forth back and
forth the voltage is switching Direction
and because of that because of ohms law
the current is switching directions also
at the same frequency 60 times per
second in this
case that is a very um
broad overview of what's going on so if
you could plot the voltage plot the
strength of the voltage you would see
that it's alternating 60 times per
second but you would see it alternating
as a sign or a cosine we call those
sinusoids and also you would see that
the current is also alternating as a
sinusoid right so the currents and the
voltages in the circuits they're all
going to look like sinusoids they're all
going to look like some kind of cosine
function that we can write down math
mathematically so that's a general
overview without any math we haven't
done anything really mathematical yet
but I wanted to give an introductory
lesson to show you what we're doing give
you a little bit of motivation explain
to you what alternating current is
before you do anything mathematical what
I like to do now is for you to follow me
on to the next section where we'll put
pencil to paper and we'll start to write
down how you would look at these
sinusoids how you would write down the
function for a voltage for instance um
mathematically and lots of different
terms we're going to be talking about
frequency and phase angle and all of
these things that sound complicated but
just remember and repeat after me none
of this stuff is hard all right none of
it's hard I can explain it to you so
it's so clear that you'll be very very
comfortable with it but you do need to
have some fundamental understanding of
trig so I'm going to take you through
that but if you have no idea what a
sinusoid is please stop now and go get
some of my lessons on trigonometry so
you're comfortable with that uh signs
and cosiness and angles and things like
that uh and then meet me back here and
we'll pick it up in the next lesson with
uh alternating current circuit
analysis
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