Ohm's Law - Simple Circuits - Free Educational videos for Students in K-12

Ohm's Law - Simple Circuits - By tecmath

Transcript


00:0-1	Good day . Welcome to take Math channel . I'm
00:01	josh . What we're going to be having a look
00:03	at in this video is Homes Law what it is
00:05	and how to use it . So let's start out
00:07	with the basics and this is not going to take
00:09	too long . So before we get to OEMs Law
00:11	, I'm just gonna quickly show you an electrical circuit
00:14	and how Holmes Law relates to this . An electrical
00:17	circuit . You know , one of these is where
00:18	we have a power source , such as a power
00:20	point or a battery as we have here with a
00:22	bunch of wires coming from it . And then we
00:24	have some fun item that we're trying to run ,
00:26	such as a light or a fan , you know
00:28	, stuff that you plug into power points or need
00:31	a battery . For the first thing we're going to
00:33	consider is this part here , which is the power
00:35	source now , power source of battery or a power
00:38	point , it provides the voltage . And when we
00:41	talk about aims law , we give this the letter
00:43	. The voltage is measured in volts and they are
00:47	also have the unit of V there and pretty much
00:51	what this is . It's the electrical potential between two
00:55	points here . So pretty much a nice way of
00:57	saying the pressure of pushing electrons down a while .
01:01	But you can just think about this as being power
01:05	. The second part that we have is the actual
01:07	power that is running along the wires here . And
01:10	I guess if we could actually have a look at
01:12	this wire hand , we could open it up and
01:14	we can see how much electricity or how many electrons
01:17	are running past a given point at a given amount
01:20	of time . This flow rate , this flow rate
01:23	is called the current . The current is the flow
01:26	rate of electrons going past a particular point . And
01:29	it's given the letter When we give homes law of
01:31	I we measure current in eps which have the letter
01:37	. I now look , I I think it might
01:40	actually stand for intensity or something like this . I'm
01:43	not 100% certain on that one . I don't know
01:45	why they didn't get the letter C . Maybe it's
01:46	going to confuse people with a cool . Um ,
01:48	but we use the letter I for that . So
01:50	current is the amount over electrons flowing down this wire
01:54	. And first off what arms law says is the
01:57	following . It says that when we consider voltage and
02:01	current , that voltage is directly proportional to the current
02:06	. That is to say if you were to increase
02:08	the voltage in this battery here , you would increase
02:11	the current going along the wires there . And if
02:13	you were to decrease the voltage of the battery here
02:16	, you would decrease the current going along the wires
02:19	. Now , these are not the only sets of
02:21	numbers that we need to consider with arms Law ,
02:23	there is one last set of numbers that we need
02:25	to think about and that is for resistance , which
02:30	when we talk about arms law is given the letter
02:33	ah and resistance is measured in homes , which is
02:36	given the greek letter omega . Now , resistance ,
02:41	if you imagine as electrons are moving along this wire
02:44	, they have all sorts of parts of the wire
02:46	that are causing resistance there impeding the actual flow of
02:50	electrons . It could be that they're made of a
02:52	different material that has more islands on it that slow
02:55	the electrons as they go along the wire might be
02:57	thinner , the wire might be longer and all of
03:00	these contribute to the resistance of that particular wire .
03:04	So how do you know what the resistance of a
03:07	particular wire is ? Well , it's pretty simple to
03:09	work out . What we would do is the following
03:12	. We could get the voltage and we could divide
03:15	that by the current and that would give us the
03:18	resistance . And this here is Homes Law . The
03:22	resistance in Homes is equal to the voltage , divided
03:26	by the current . Now , this is usually written
03:28	a little bit differently . And you might have seen
03:29	this written depending on whether we're talking about voltage ,
03:32	current or resistance . We could change this all around
03:36	and we can actually say , okay , what we
03:37	have is we have the voltage and that's equal to
03:40	the current multiplied by the resistance . Or we could
03:43	also say that we have the current and that is
03:47	equal to the voltage divided by the resistance , depending
03:50	on how we ordered that particular equation . But just
03:52	one little thing , there's a really , really easy
03:54	way that we can actually remember this and I'm going
03:56	to show you this right now . We can put
03:58	all of this together in a triangle known as the
04:01	OEMs Law triangle , where we can say voltage is
04:05	equal to the current multiplied by the resistance . Let
04:09	me show you how this particular triangle here works .
04:12	So so we wanted to work out voltage here .
04:14	We put our finger over the voltage and as you
04:17	can see , current is sitting next to resistance there
04:20	. It means we multiply these guys . So voltage
04:22	is equal to current . Multiplied resistance . Say we
04:25	were trying to work out the current . I put
04:26	my finger right here and I could say the current
04:29	is equal to the voltage over the resistance voltage divided
04:33	by the resistance . Finally , we can look at
04:35	the resistance and I can say , okay , what
04:37	we want to do is we want to know what
04:38	the resistance is . The resistance we put our finger
04:40	here is equal to the voltage divided by the current
04:44	. So as you can see here this saves you
04:47	remembering a whole bunch of formulas , you have it
04:49	all written there and all you really need to know
04:51	is that voltage is equal to current , multiplied by
04:55	resistance . You draw a triangle there and then you
04:57	can start working at all sorts of things there .
05:00	But as you can see voltage current resistance are totally
05:03	related to one another . So let's do some problems
05:06	that you might encounter with James Law . So I'll
05:09	get rid of the used to start off with and
05:11	once again I'll draw my own law triangle over here
05:15	. Okay so always a good way to start .
05:17	I'll keep it there and it's going to be voltage
05:20	is equal to the current , multiplied by the resistance
05:24	. So I have my own law triangle . Now
05:27	let's go through and put some values into our particular
05:30	diagram here . We'll get a bit fancy with our
05:32	diagrams and do some proper diagrams in a minute .
05:34	But let's start with this diagram and say for instance
05:37	we had a six volt battery . And then what
05:41	we did is we got an ammeter and we're actually
05:44	measured how much current is going through the wires here
05:48	. And when we did that we found out that
05:49	we had a current of 1.5 amps . Okay I
05:55	is equal to 1.5 amps . And you know what
05:57	I'm going to ask are we going to say ?
05:59	Okay well what is the resistance equal to ? Okay
06:02	. So how much is resistance and how do we
06:06	go through and work that out ? Well it's pretty
06:07	simple . We use our Homes law triangle . Here
06:09	we go . The resistance . Put our finger here
06:12	and it's equal to the voltage over the current .
06:16	So equals the voltage over the current . All right
06:19	, let's work this out . What's the voltage ?
06:21	Well , you can see it's 6V and the current
06:23	is 1.5 amps . Six divided by 1.5 . We
06:28	get our answer . Six divided by 1.5 . We
06:31	have four homes . Is the resistance . Cool .
06:36	Well let's do another one of these . So let's
06:39	draw one more circuit up . I'm going to draw
06:40	the proper schematics on this one this time . So
06:43	first off , we have the power source and this
06:45	is how you draw these guys . We have the
06:47	big line here , which is the positive , the
06:49	little line here , which is the negative . We
06:51	have the wire coming off from that . And we're
06:53	going to show resistance . Resistance is shown through this
06:57	line here , This symbol here and then the conductor
07:00	goes all the way back around to the negative terminal
07:04	there . Let's put some values on our diagram .
07:06	Okay , so what we have here is an 18
07:09	volt battery and we have a resistance that we know
07:12	which is 24 homes . And you know , we're
07:15	gonna be trying to work out , we're going to
07:17	try and work out what the current is . So
07:20	how do we go about doing this ? Well ,
07:22	first off , let's draw up our homes law triangle
07:26	. We have voltage eagles , current multiplied by resistance
07:30	. We're trying to work out the current right here
07:32	. So this is the current is going to be
07:34	equal to the voltage divided by the resistance . Okay
07:39	, so what have we got here ? We have
07:40	the voltage which is 18V . We have the resistance
07:44	which is 20 for OEMs and we can work this
07:48	out 18 divided by 24 . We get our answer
07:51	which is a current of 0.75 apps . Okay ,
07:57	let's do some more of these . So I'm gonna
07:58	put up five more of these and do as many
08:00	as you need to . It's well worth getting used
08:02	to these as they are needed in the next steps
08:04	. When we look at series and parallel circuits by
08:06	the way , if you like this video , let
08:07	me know and subscribe . But here's some more questions
08:11	how many nights I was gonna do ? We're gonna
08:13	do five more . Okay . The first of five
08:17	questions an iPod uses a 1.5 volt battery . It
08:22	has a current of 0.01 apps . What is the
08:26	resistance in the circuit ? So you know how we're
08:28	going to solve this . First off , we're going
08:30	to draw up our homes law triangle . That voltage
08:35	is equal to current multiplied by resistance . And we're
08:38	trying to work out the resistance . The resistance is
08:40	equal to the voltage divided by the current . Resistance
08:44	equals voltage divided by the current . And this is
08:48	going to be equal to the following . We have
08:50	a voltage of 1.51 point five volts and we have
08:54	a current of 0.1 amps . Nice and easy .
09:00	1.5 divided by 0.1 We get our answer here .
09:05	We have a resistance of 150 homes Nice and easy
09:11	. Cool . What about we do a second question
09:14	. Okay , a second question . A 12 volt
09:17	car battery runs a headlight whose circuit has a resistance
09:20	of 15 homes . How much is the current we're
09:22	talking about here ? So what would I do first
09:25	? I draw my Homes Lord Triangle up . And
09:27	I'm gonna say voltage equals current multiplied by resistance .
09:31	We're trying to work out the current here . So
09:33	current is equal to voltage Divided by resistance . So
09:37	current is equal to voltage divided by resistance which is
09:41	equal to the following . The voltage is 12V .
09:45	We have the resistance which is 15 homes . And
09:49	we're gonna get the answer . It's going to be
09:51	an amps . 12 divided by 15 . We get
09:54	our answer of 0.8 amps the current 0.8 apps .
09:59	These are pretty easy . Right ? Okay . Third
10:02	question . A light bulb has a resistance of five
10:05	homes with a maximum current of 10 apps . What
10:08	is the maximum voltage that can be used ? So
10:11	once again let's put our Homes Law Triangle there .
10:14	Good practice . Just get really used to it ,
10:16	voltage equals current , multiplied by resistance . We're trying
10:20	to work out voltage . So we're gonna go voltage
10:22	equals current , multiplied by resistance . Nice and easy
10:26	when it's gonna be multiplying we have a current which
10:29	is 10 amps and we have a resistance which is
10:32	five homes . So five OEMs . What we get
10:36	10 times five . We have 50 volts . So
10:40	the maximum voltage that can be used is 50 volts
10:43	. Alright , our fourth question . And you can
10:45	see I've even stopped them and writing proper questions these
10:47	days we have 41.5 volt batteries . So four by
10:51	1.5 . We have total of six volts running into
10:54	this particular circuit . And we have the bulb which
10:57	has a resistance of three homes . Okay , So
11:00	what current is needed to power this ? All right
11:03	. So , how we go about doing this ?
11:05	All right , Pretty simple . We draw up our
11:08	triangle and we say that voltage is equal to current
11:12	, multiplied by resistance . We're trying to work out
11:15	the current . So the current here is equal to
11:18	the voltage divided by the resistance . Nice and simple
11:22	. We have the voltage that is six volts .
11:25	And we have the resistance of three homes and everything
11:29	works out nice and easy . Six divided by three
11:31	. We have 22 amps . So we have two
11:34	amps of current running through that wire . All right
11:37	, we're going to get to that last question .
11:39	Okay , Final Question . Toy has 31.5 volt batteries
11:43	. The current is 0.5 amps . What is the
11:45	resistance ? So let's draw this up first . We
11:48	have our Homes law . Triangle voltage equals current times
11:53	resistance . We're trying to work out the resistance .
11:55	So the resistance here is going to equal the voltage
11:59	divided by the current . Easy . All right .
12:02	So what's the voltage ? It has three times 1.5
12:05	batteries . So three times 1.5 we have 4.5 volts
12:10	. So let's put that in 4.5 volts And the
12:13	current is 0.5 amps . Let's put that in 0.5
12:17	amps 4.5 divided by 0.5 . That is going to
12:22	equal nine . And the unit we use for resistance
12:24	once again is Homes . Because OWNS is all about
12:28	resistance . Anyway , Thank you for watching . There
12:31	is an upcoming video where we're going to be looking
12:33	at series and parallel circuits and it's really worth knowing
12:36	your Homes law if we're going to get into those
12:39	anyway . I hope you like that video . Like
12:41	subscribe . You know the rest . Thank you for
12:44	watching . See you next time . Bye .

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