0:01

This week, we're going to continue our discussion of some simple DC circuit

concepts. We're going to begin by discussing energy

and power, to make sure that those fundamental concepts are clear.

Then, from there, we can go on to calculate the power dissipation, or the

power delivered by simple circuit elements, such as batteries and

resistors. Now, after that's understood, we can then

talk about the important concept of impedance managing, and that has to do

with power transfer from one part of a circuit to another.

And that's important, for example, in a guitar amplifier, when we have to

impedance manage the amplifier. To the loud speaker.

So we get maximum efficiency out of the system.

after that, we're going to go on and talk about real current and voltage sources,

as opposed to ideal sources, such as a battery as an ideal voltage source.

But we're going to talk about the effects of, of real sources and how to model

those sorts of things. And then following that, we'll talk a

little bit about an idea called a dependent source.

So you can have dependent voltage and current sources.

And that leads us to the idea of the operational amplifier.

Which can be represented as a, A dependent voltage source.

And we need to develop a simple model of the operational amplifier, or just the op

amp. So we can discuss in more detail the

types of circuits that appear in the guitar amplifier.

1:51

Okay, first of all I'd like to talk a little bit about energy and power.

To make sure that you understand the difference clearly.

Now power is energy or work. Work and energy are the same.

So power is energy done per unit time. Or energy expended per, per unit time.

Now, energy, as you remember, is measured in joules.

And a joule is a force times a distance. One joule is one Newton times one meter.

So, the if, I'd to look at the units of things to keep straight in your mind what

we're talking about. And, also it's, it's it's very helpful

for checking the results of problems that to make sure that the units are right in

the end. But anyway joule, force times distance.

Force is mass, kilograms, times acceleration.

So it's ma times a distance. And so the units of a joule is a kilogram

meter to the second power per second squared.

Now a watt is equal to one joule per second, and the units of a watt, that's a

force times a velocity. So a force times distance, that's a

joule, but, distance divided by time, that's a velocity.

So force times velocity is the, the the quantity that is equal to watts.

So that's kilogram meters squared per second to the third power.

And that is energy per unit time. So there you have it.

That's the definition of a watt. Now, here's a, a little, illustration to

show the difference between energy and power.

So we're going to push these blocks up these inclined planes, and it takes

energy, to do that. There's going to be, the energy of the

block is greater at the end after I've pushed it up to the top of this slope,

and so If you see on the left, I, the block moves up over the course of about

three seconds and on the right it goes up one second.

Now the energy gained is the same in both cases.

It's the same amount of work has been done, the same amount of energy has been

given to that block, but this, the, the, on the right, that happens about three

times faster, and so that's actually three times the power.

So, let me just back up and see it again. So, we did the same exact amount of work.

But the power is three times greater over here, but we only had to exert that power

for one third of the time. So you see, energy is the power times the

time. That's the same equation as this.

And so If I triple the power but, cut the time down by a factor of three it's the

same total energy. Now just as a interesting aside the

National Ignition Facility has one of the world's most impressive lasers certainly

the world's most impressive laser. This, it's 192 laser beam system that

delivers 500 trillion watts of power. That is equal to a 1000 times the US

power consumption. But here's the catch.

It can only deliver that in a pulse that's just a few nanoseconds long.

So it's something on the order of 3 or 4 times 10 to the minus 9 seconds.

So if you calculate the power, 500 terawatts, 500 times 10 to the 12.

Times 3.6 times 10 to the minus 9 seconds, that comes out to 1.8 mega

joules, 1.8 times 10 to the 6th joules. so a mega joule, that sounds like a, a

lot of energy, but it's really not if you look up the energy content of gasoline,

that's about the same amount of energy content if you burn 50 milliliters of

gasoline. so, the thing about this laser is it can

deliver that much power in a very short period of time.

So, the it's clear that this is a not a huge amount of energy, but it's one heck

of a lot of power. [BLANK_AUDIO]