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Ohm`s Law Simple Examples

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Subido el 7 de noviembre de 2013 por Samuel E.

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Ohm`s Law - Three Simple Examples

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We're still talking about Ohm's Law, which is commonly written as V equals IR, 00:00:00
and we're going to work through three simple example problems with Ohm's Law. 00:00:06
Now, even though it's commonly written this way, remember that there are other ways we can write Ohm's Law. 00:00:10
We could take the equation V equals IR, and we can divide both sides by R, as we did before, 00:00:15
and when we do that, the R's cancel out on the right, and that leaves us with an I on the right equal to V over R. 00:00:22
So instead of being written like this, V equals IR, it could also be written like this, I equals V over R. 00:00:30
And there's another thing we can do. 00:00:38
We can take the equation V equals IR, and we can divide both sides by I. 00:00:39
And when we do that, the I's on that side cancel out, and we're left with R equals V over I. 00:00:48
So Ohm's Law could also be written like that, R equals V over I. 00:00:56
these three equations are all mathematically equivalent they're all really the same equation 00:01:02
just algebraically arranged differently and we'll do an example problem with with the equation in 00:01:08
each of those three forms here's the first one a 12 volt battery is connected to a light bulb 00:01:14
with a resistance of three ohms how much current flows through the light bulb well the 12 volts 00:01:20
when it says there. That's the voltage. So I'm going to write V equals 12 volts. And it's connected 00:01:27
to a light bulb with the resistance of 3 ohms. So that's the resistance. So I'm going to write 00:01:33
R equals 3 ohms. And you see the symbol omega is the symbol for the resistance, for the unit of 00:01:38
resistance, the ohms. And we're trying to find the current, how much current. So I is what we don't 00:01:49
know, we can use the equation in this form, I equals V over R. And we just put in the 00:01:56
numbers that we know for V. V is 12 volts, R is 3 ohms, and when we divide we get 4, 00:02:04
and the current is in amps, and we use the symbol A for amps or amperes. In this example 00:02:12
we're told that a large electric heater is designed to draw 40 amps of current, and 40 00:02:19
is a lot of current. Just to give you an idea, I hooked up a meter to my stove. 00:02:24
I have a regular, it's a regular electric stove with four burners, and I put them 00:02:29
all on high, and with all burners on high it was drawing 28 amps of current. So, and 00:02:34
you typically don't run the stove with all four burners on high, but that gives 00:02:41
you an idea of how much 28 amps is. Your electric stove, turn everything on high, 00:02:43
that's it. So this is 40 amps of current, that's a large heater. Alright, let's look 00:02:49
the problem. If the resistance of the heating element is 5.5 ohms, so that's the resistance 00:02:53
R, 5.5 ohms, and we're also given here the 40 amps, that's the current. So I'll write 00:02:59
I for current is 40 amps. And we're asked how much voltage, the voltage is what we're 00:03:09
looking for. So we just use the equation in this form, V equals IR. So it's just a simple 00:03:16
multiplication. 40 amps times 5.5 ohms, and it comes out to 220 volts. That's our answer. 00:03:23
Now that's a lot of voltage. Now you might remember I said that a regular electrical 00:03:36
household outlet has 120 volts, or sometimes it's 110. So one of these outlets on your 00:03:40
wall that looks like this is 120 volts. So you obviously couldn't plug this heater into 00:03:48
that outlet you need it to match this heater is designed to use 220 volts but if you go in your 00:03:53
house and you look say behind your dryer your dryer uses a lot of electricity there's a heating 00:03:59
element in there and a big fan and it takes a lot of energy to heat those clothes up enough to dry 00:04:05
them and there's a plug probably on the wall behind the dryer that looks something like this 00:04:10
and it's got three holes right there and the plug on the back of your dryer that you plug 00:04:15
into the to the socket is shaped to fit there and it won't plug into a regular outlet this is a 220 00:04:21
volt outlet and you most people have one of those in their home and this is 120 volt outlet here 00:04:28
so this you could have a heater that runs on 220 volts but you would need to plug it into a 220 00:04:34
volt outlet like this most of the stuff in your home though goes on the regular 120 or 110 00:04:40
and one more when a certain light bulb is connected to a 1.5 volt battery okay so that's 00:04:46
our voltage v is 1.5 volts 0.25 amps of current flow so that's the current and i is our symbol 00:04:54
for current and it's 0.25 amps 0.25 amps of current flow through the bulb what is the resistance the 00:05:03
resistance is what i don't know so i'll use the equation in this form r equals v over i 00:05:10
and I put in 1.5 volts and 0.25 amps 00:05:16
and I do the division 00:05:21
and it comes out to 6 00:05:23
and when you divide volts by amps 00:05:24
you get ohms 00:05:28
so this is 6 ohms 00:05:29
that's the resistance in this particular case 00:05:31
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Idioma/s:
en
Etiquetas:
EducaMadrid
Autor/es:
Derek Owens
Subido por:
Samuel E.
Licencia:
Reconocimiento - No comercial - Compartir igual
Visualizaciones:
21
Fecha:
7 de noviembre de 2013 - 12:17
Visibilidad:
Público
Centro:
IES JOAQUIN ARAUJO
Duración:
05′ 38″
Relación de aspecto:
1.76:1
Resolución:
480x272 píxeles
Tamaño:
5.62 MBytes

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