Ohm’s Law Tutorial with easy practice problems | Basic Circuits
Summary
TLDRThis tutorial delves into Ohm's Law, a fundamental principle in electrical engineering that links voltage, current, and resistance. The presenter explains that Ohm's Law is expressed as V=IR, where V is voltage, I is current, and R is resistance. They clarify the linear relationship between these variables and how changes in one affect the others. The video includes practical examples to demonstrate how to calculate current using Ohm's Law in simple circuits. It also touches on the concepts of resistivity, conductivity, and the significance of Ohm's Law in various electrical applications. The presenter emphasizes the importance of understanding Ohm's Law for future studies in circuit analysis and electrical engineering.
Takeaways
- 🔌 Ohm's Law is a fundamental principle in electrical engineering that relates voltage, current, and resistance in a circuit.
- 🌊 The script uses the analogy of water flow to explain the concept of resistance, which is a force that opposes the flow of current in a circuit.
- ⚡ Ohm's Law is mathematically expressed as V = I * R, where V is voltage, I is current, and R is resistance. This formula can be rearranged to solve for any of the variables.
- 🔄 The relationship between voltage, current, and resistance is linear, meaning changes in one variable will proportionally affect the others.
- 🔍 Resistivity is mentioned as a different concept from resistance, but it is not the focus of the script.
- 📐 Ohm's Law is applicable to resistors, which are considered linear components in most cases for simplification in calculations.
- 🔄 The script emphasizes the importance of understanding the direction of current flow and keeping consistent with the chosen perspective throughout calculations.
- 🌐 The concept of 'ohms' as a unit of measurement for resistance is introduced, along with the concept of conductivity, measured in siemens or mhos.
- ⚠️ Two extreme cases of Ohm's Law are explained: a short circuit (R = 0, resulting in infinite current) and an open circuit (R = ∞, resulting in zero current).
- 📝 Practical examples are provided to demonstrate how Ohm's Law can be applied to simple circuits to calculate current, emphasizing the importance of understanding relative voltage differences rather than absolute values.
- 📚 The script concludes by highlighting the importance of Ohm's Law in further studies of circuits and electrical engineering.
Q & A
What is Ohm's Law and how does it relate to voltage, current, and resistance?
-Ohm's Law is a fundamental principle in electrical engineering that states the relationship between voltage (V), current (I), and resistance (R). It is expressed as V = I * R, meaning the voltage across a resistor is equal to the current flowing through it times the resistance of the resistor.
What is the significance of Ohm's Law in circuit analysis?
-Ohm's Law is significant because it provides a linear relationship between voltage, current, and resistance, which is a foundational concept used in all levels of electrical engineering and circuit analysis. It allows for the calculation of unknown quantities in a circuit when two of the three are known.
Can Ohm's Law be rearranged to solve for different variables?
-Yes, Ohm's Law can be rearranged to solve for any of the three variables (voltage, current, or resistance). For example, it can be rearranged to I = V/R to find the current, or R = V/I to find the resistance.
What is the difference between resistivity and resistance mentioned in the script?
-Resistivity is a material property that quantifies how strongly a given material opposes the flow of electric current. Resistance, on the other hand, is the opposition to the flow of electric current in a specific component or part of a circuit, which depends on the resistivity of the material, its dimensions, and shape.
What are the two extreme cases of Ohm's Law mentioned in the script?
-The two extreme cases of Ohm's Law mentioned are when resistance is zero (short circuit) and when resistance is infinite (open circuit). In the short circuit case, the current would be infinite if the voltage is not zero. In the open circuit case, the current would be zero regardless of the voltage.
What is the term used for the reciprocal of resistance, and what are its units?
-The reciprocal of resistance is called 'conductivity'. Its units can be expressed in mhos or siemens (symbolized by 'S'). For example, if a resistor has 100 ohms of resistance, its conductivity would be 1/100 siemens.
How does the script illustrate the concept of voltage being relative?
-The script illustrates the concept of voltage being relative by explaining that the voltage across a resistor is the difference in potential between two points, regardless of the absolute values of those points. This means that the voltage is comparative and depends on the potential difference, not the actual values.
What does the script suggest about the direction of current in a circuit?
-The script suggests that the direction of current in a circuit is a matter of perspective and should be consistently maintained once established for the purpose of calculations. It emphasizes that the direction should not be changed midway through calculations to avoid confusion.
How does the script handle negative voltage values in circuit analysis?
-The script handles negative voltage values by treating them as relative to an arbitrarily decided zero potential point. It emphasizes that the key is the potential difference between two points, and the actual sign (positive or negative) does not change the analysis as long as the relationship is consistent.
What advice does the script give for solving problems using Ohm's Law?
-The script advises to write down the chosen direction of current and the setup of the problem once decided, and to stick with it throughout the calculations. It warns against changing the direction or setup midway, as this can lead to confusion and errors.
Outlines
🔋 Understanding Ohm's Law
The first paragraph introduces Ohm's Law, explaining the relationship between voltage, current, and resistance. It discusses the concept of resistance, how it affects the flow of current, and presents Ohm's Law as a mathematical equation: Voltage (V) equals Current (I) times Resistance (R). The paragraph also emphasizes the linear relationship between these variables and how this principle is foundational in electrical engineering, crucial for circuit analysis.
⚡ Short Circuits and Open Circuits
The second paragraph discusses the extremes of Ohm's Law: short circuits and open circuits. It explains that a short circuit occurs when resistance is zero, leading to an infinite current, often causing circuit damage. Conversely, an open circuit happens when resistance is infinite, resulting in zero current flow. These concepts are critical in diagnosing and understanding circuit behavior, with practical examples provided to illustrate these scenarios.
🔄 Importance of Voltage Potential
In the third paragraph, the focus is on the concept of voltage potential and its relative nature. The example given shows how voltage differences across a resistor affect current flow, using simple circuit setups to demonstrate the point. The paragraph also touches on the importance of consistency in analyzing circuit direction and potential, emphasizing that voltage is relative and must be considered in context.
💡 Practical Application of Ohm’s Law
The final paragraph wraps up the discussion by reinforcing the application of Ohm's Law in practical circuit analysis. It reiterates that understanding voltage differences and maintaining a consistent approach is key to accurate calculations. The paragraph also encourages further learning through additional examples and resources, while highlighting the enjoyment and importance of circuit analysis in electrical engineering.
Mindmap
Keywords
💡Ohm's Law
💡Voltage
💡Current
💡Resistance
💡Resistivity
💡Linear Relationship
💡Circuit
💡Ohms
💡Conductivity
💡Short Circuit
💡Open Circuit
Highlights
Introduction to Ohm's Law and its relation to voltage, current, and resistance.
Explanation of the difference between resistivity and resistance.
Ohm's Law formula V = IR, and its rearrangements to solve for different variables.
Intuitive understanding of Ohm's Law using the water flow analogy.
Linear relationship between voltage, current, and resistance in resistors.
Practical application of Ohm's Law in circuit analysis.
How to use Ohm's Law to calculate current with given voltage and resistance.
The significance of Ohm's Law in electrical engineering and its wide applicability.
Introduction to the concept of ohms as a unit of measurement for resistance.
Explanation of conductivity as the reciprocal of resistance.
Two extreme cases of Ohm's Law: short circuit and open circuit.
Practical examples of applying Ohm's Law in simple circuits.
The importance of maintaining the direction of current in circuit calculations.
Understanding the concept of voltage potential and its relativity in circuit analysis.
The impact of negative voltages and their role in circuit analysis.
Final thoughts on Ohm's Law and its foundational role in further circuit analysis.
Transcripts
[Music]
today we're going to talk about
ohm's law so in the last tutorial we
talked about voltage
current power and energy well we talked
about a glass of water in the flow and
all that sort of stuff
but the flow isn't always free sometimes
there's something that makes it so this
the flow is resisted and that is called
resistance
and today ohm's law is the way we're
going to relate voltage and
current because they are definitely
related now i'm just going to point out
that there is resistivity and resistance
and right now i'm just going to ignore
resistivity but it is something
different and so
when we're talking about this say
resistance so we have a very simple law
that compares
voltage current and resistance and that
is called ohm's law
so ohm's law is basically v
voltage equals the current i
times resistance and that can very
easily mathematically be switched so you
have
voltage over the resistance that v looks
terrible as always equals current
and you know honestly we could do
voltage over
current equals resistance you can move
this thing around however you want
but i typically like to see it in this
way it's a
pretty way for me but honestly the
voltage over resistance equals current
it's probably the best intuitive way to
understand this
and as you can see here so if you have a
voltage you
lift that glass higher if you have the
same amount of resistance you're going
to have more current
but if you have the same voltage and you
increase the resistance
you're going to decrease the current so
one of the things about this is you'll
notice this is a very linear
relationship
if you change any of these the other
things are going to change
linearly and this is not the case with a
lot of components but with resistors we
typically treat them as linear
and we don't really worry about those
other cases in the vast majority of time
so voltage over resistance equals
current
this
is so huge it's going to be used in
basically everything every
circus class from here until forever and
then a lot of the things in electrical
engineering still refer to this even if
it's not
circus related so this is an incredibly
important thing
and also very straightforward and you're
going to learn a lot about it but let's
go over it a little bit more
so if you are given a circuit let's just
put a node right here
a resistor and then another node
we already have everything we need to
solve something so let's say
this is going to be 100 volts and this
is
0 volts so now we have 100 volts across
this resistor and then let's say this
resistor is
100 ohms
we can use ohm's law to very easily say
okay we have the voltage and we have the
resistance so we'll want to use this
format
we'll say 100 volts over
100 ohms equals
one amp okay that seems super simple and
it is super simple
it gets much more complicated but that
is the essence
of how you can use ohm's law to solve
for the current or if you happen to know
if you happen to know what the current
is
then you can do the same thing i'm
saying oh i know i have one amp through
here and there's 100 volts across it so
whatever i need so you can use any of
these you just need to have two
and then you'll figure out the other one
so this is pretty simple
and you notice i use the word ohms and
it's
wow that is and i apologize my
handwriting is so
so bad but this is a greek omega let's
see if it can look a little bit better
no that just looks like some sort of
farming implement now
but that is what that symbol is that
means ohms and that is the measurement
of resistance now there's actually
something out there that
is called a mo and it's an upside down
oh my goodness that's really going to
stretch my ability
and that is 1 over
r and that is called conductivity and
that can be mohs or
siemens whatever you want so 100 ohms
would be one over 100
siemens and that's just an s
or you can also do one over 100
moes and you're not really going to see
that
that often at least i haven't if you do
well great i'm glad that i've introduced
it but
you might hear that on occasion and
that's the only reason i wanted to
introduce it to you
but in my career and in my time in
college i
very very rarely saw that so if you do
that you can totally change ohm's law to
again
follow those rules but now that i've put
that out there we are going to
completely
ignore this ever again so enjoy
so before we get into the samples i just
want to give two cases of the extremes
of ohm's law
so if you have v equals ir imagine
your r is zero so you have
v over r
which equals zero what does that come
out to be
it comes out to be infinity and that is
called a short circuit
and that's something what happens if you
take a battery and you just put a wire
from one end to the other
that wire is essentially zero resistance
so that battery outputs as much
current as it possibly can until it
melts and everything goes away
in most cases you don't want that some
cases you might
i think when you are doing welding they
try and get that is
that resistance as low as possible so
that they can get as much heat there
as possible but this in general is
something
we want to avoid because it usually
means your circuit's about to blow up
now let's say we have the opposite
problem voltage
over infinite resistance
okay there we go then what is our
current going to be
it's going to be 0 get the exact
opposite and this is called an open
circuit and sometimes this is what you
want sometimes this isn't what you want
sometimes when you have a circuit and
you're testing things and you
are not getting any current it's like oh
okay that means that i have an
open somewhere in this and if it's on
your circuit board and you can't see
where it's
broken that's a problem but at least you
know from there being a complete
lack of current that is is an open
circuit so those are the two extreme
cases
of ohm's law when resistance is zero and
when resistance is infinity
and how that affects your current i
so with that out of the way let's
actually jump into a couple of examples
so we can see
how this is used practically now we're
not going to be able to solve anything
crazy or anything
truly that interesting until we learn a
couple of more tricks
but at least we'll have a couple of
examples of how to do
ohm's law in very simple circuits
okay so the first circuit that i'm going
to set up here after that super simple
circuit that we had oh man okay i'm just
going to stop complaining about that
and keep on going is we are going to
have 15 volts
here 5 volts here
and 200 ohms right there
so when you're dealing with voltage
potential and it's that voltage across
something and that's what's important
so when i'm holding the glass here it
doesn't matter
that i'm actually in the basement right
now because all i care about is from
here
to here now from here to here was
sitting on the roof of my house
or on the roof of our office that
distance is still the same
so voltage potential can move like this
and as long as that distance between the
two points is the same
it really doesn't matter so with that in
mind let's look at this and now
we are going to have our v over
r equals i oh that's a one
but now our v is actually 15 volts
minus 5 volts over 200 ohms
which equals 10 volts over 200
ohms so now we're just getting 1 20th
1 over 20 which is about .05 amps
or 50
milliamps so the key thing that i want
to take away from this is it doesn't
matter that this was 15 volts or
5 volts because we could do this exact
same circuit
at 10 volts 0 volts 200 ohms
and then we'd still have 10 volts minus
0
over 200 wow
that got out of control and that's still
going to equal
0.05 amps
so that is what i wanted to do this for
it's just to show
that voltage is all comparative i could
even go the other way around
i could do that as negative 10 volts to
negative 20 volts it's still going to be
the same
thing so voltage is all relative it's
that potential between
or across between two points across
something else
so let's do another one
with my paper okay so two more quick
examples so this first one
i am and notice how i'm keeping these
simple i'm trying to keep the math
simple because to me it's more about the
intuitive understanding
you can use a calculator to get to do
the crazy math but
if you want to be able to look at it and
figure out how to solve it you need to
understand
oh hey that's actually that way i can
flip that or i can move that and it
won't actually affect anything so that's
that's where i'm going with this so
let's actually
assign this 10 volts
and assign this 20 volts
and then we will say this is
100 ohms again just for the fun of it
so now i'm going to set the equation up
and
this is something i always did in
college and i still do quite a bit
i'll just write ohm's law in the corner
just to make sure that i'm not screwing
anything
up so i'll have 10 volts
minus 20 volts
over 100 ohms which equals
negative 10 volts over 100 ohms
which equals negative 1 10
amps or 100
milliamps negative 100 milliamps okay so
negative 100 milliamps what does that
mean
well that means that we looked at this
and the way it's set up you'd imagine
okay glass is up here
but actually this is completely flipped
where the higher potential is down here
so even though we have
established that our current is going
this way in reality it's going
the opposite way but since we
established that the current is going
that way we want to say
negative 100 milliamps and that is an
incredibly important thing to remember
and something i still screw up with
ohm's law
is you need to say i am going to say
that i'm going from this point to this
point my current is going
this direction and i am sticking with
that because if you say oh that's
negative well let me just flip things
around you
highly highly increase the chance of you
messing up your math somewhere so what
you do is you set up the equation you
look at it
you say hey this is the way it's going
to be and then i'm just going to take
the signs as i go because if i take this
and i
switched it and i did all the math
differently and
went back up then it would be okay 20
volts
minus 10 volts over 100 ohms
and then i'm going to get 100 milliamps
but it's going to be in the opposite
direction
so that was the key with this one that i
want you to take
away is that that positive and negative
is
a matter of perspective it's a matter of
which way you're looking at it so
always keep that in mind and make sure
that once you
say i'm going to do this and i highly
recommend writing it down
on the paper as you're doing it once you
say this is how i'm doing it stick with
it
don't switch it don't change your mind
or else you're just going to confuse
yourself
or if you do switch your mind switch
your setup because you realize oh man
that's going to be a complete nightmare
just be very very careful with that okay
let's do
one more all right so this will be our
last example so let's do the same things
we've been doing the ugly resistor
the ohm's law in the corner and then
let's just say
this is negative 15 volts
and this is negative 25 volts
and then let's make this 1000 ohms
just because i'm getting bored with 100
okay so we set up ohm's law and we look
at this and we say okay
what's the difference between those
that's negative 15 volts
again based off of what we just
discussed i'm assuming that our current
is flowing
down so we've got negative 15 volts and
then got a minus that
one but that's minus negative 25 volts
and then over 1 000
ohms well negative 15 minus negative 25
is a positive 10. so that actually
becomes a positive number
you've got 10 over 1000 which equals 1
over 100
which gives us .01
or 10 milliamps
[Music]
okay maybe i should just i'm going to
learn some great things while doing this
about
calm handwriting maybe everything will
make sense
but the point i wanted to bring with
this was again that
different potential it doesn't matter so
even though this is a negative number
and this is a negative number
it's all about the relationship between
the two
it's all about that voltage across
this so just because this is negative 15
and negative 25
in this case because there's nothing
else those numbers are basically
arbitrary again you could go and have
10 and 0 and it acts the exact
same way now if this were part of a
bigger circuit then of course it makes a
huge difference
but negative voltages in general just
mean that they're on the different side
of a
an arbitrarily decided a zero again we
shoot in my basement
all of these circuit bread tutorials are
shot in my basement
so we are beneath the ground i can see
through the window there's that
so if we assume ground is zero
everything we do here is below that zero
but it still functions
if we were on the roof if we are on top
of a skyscraper it more matters about
what the difference is and so i'm going
to establish
that for where i am this point is zero
or i could establish that point being
zero it really doesn't matter that
voltage can be
very very different depending on what
perspective
you have looking at it so that's it
that's ohm's law hopefully i gave you a
good overall view of what it is
gave you a couple of examples and how
you can use it to solve
extremely simple circuits next we're
going to go into a couple more
definitions talking about branches nodes
all that sort of stuff
and then after that we'll be able to
start doing a little bit more
complicated circuit analysis
in which time i'm going to be super
excited because this is a lot of fun for
me i love doing circuit analysis i'm not
good at it
but i enjoy it so hopefully that was
helpful again as always we put a written
tutorial on circuitbred.com link is down
in the description
so if you have any more questions i want
to see a couple of different examples
those are on the written tutorial it's
going to be slightly different than what
we've done here today
so if you have any great questions you
can put them either here in the youtube
comments or over on circuitbred.com in
the comments
and we will catch you in the next one
have a good one
you
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