Exploring Circuits - Free Educational videos for Students in K-12

Exploring Circuits - By MITK12Videos

Transcript


00:05	In today's lesson , we're going to explore some simple
00:08	electric circuits . Circuits can be found in every corner
00:11	of your house , but how do they work ?
00:13	And what tools the engineers used to design them .
00:15	Engineers use pictures called circuit diagrams to visualize electric circuits
00:20	. This diagram shows a simple circuit in which a
00:22	battery provides a potential that drives an electric current through
00:26	a resistor . Recall that OEMs Law relates the important
00:30	circuit properties , potential current and resistance . The potential
00:34	drop across the resistor is equal to the current flowing
00:37	through that resistor times the value of the resistor .
00:42	This water experiment provides an analogy where we can better
00:45	visualize potential current and resistance in a circuit here ,
00:51	electric potential is related to the height of the water
00:54	. The water starts at the top of the funnel
00:57	And drops 18" to the flask at the bottom .
01:00	This is a potential drop of 18" . Electric current
01:05	is related to the flow of the water through this
01:07	circuit We start with 100 mL of water at the
01:11	top and it all drains to the bottom in 20
01:13	seconds . This is a current Of five mm/s .
01:18	The resistance is related to the number of loops .
01:22	The more loops you have , the more resistance .
01:26	Now let's look at potential current and resistance in an
01:29	electric circuit . Our battery provides 9V of potential to
01:33	drive current through resistor 1500 homes . Pause this video
01:37	and try using arms law in these circuit parameters to
01:40	calculate the current when you come back . We'll measure
01:43	it using a meter . Engineers use a tool called
01:47	a digital multi meter to measure current and potential and
01:49	electric circuits to measure current . The meter must be
01:53	set up in current mode . This means placing the
01:55	red lead into the current slot and turning the dial
01:58	to a for amps . Let's look at our circuit
02:01	diagram to see where the meter goes in order to
02:04	measure current . You must first break the circuit And
02:08	place the meter such that the current flows from the
02:10	battery through the meter and then three year resistor .
02:15	The meter shows that the current is 0.5 amps .
02:18	How does this compare to your calculated value from OMs
02:21	law ? It should be pretty close to measure potential
02:24	using a digital multi meter , the media must be
02:27	set up in potential mode . This means moving the
02:29	red lead to the potential slot and turning the knob
02:32	to V . For volts . Let's look at our
02:34	circuit diagram to see where the meter goes . We
02:37	measure potential . We must measure it across a circuit
02:39	element . This means placing the red lead of the
02:41	meter on one side of the element and the black
02:44	lead on the other . Our meter shows the potential
02:47	drop across the resistor is 8.93V . This is very
02:51	close to the battery potential of 9V . Let's move
02:55	on to explore some more complicated circuits . Series circuits
02:59	consist of elements that appear one after another , where
03:02	parallel circuits elements appear side by side . Let's investigate
03:07	how potential and current properties differ between these two circuit
03:10	types . The diagram on the left represents a series
03:13	circuit where a battery supplies current that flows through two
03:17	resistors , placed one after another . On the right
03:20	are the series circuit properties . The first talks about
03:23	potential . The potential supplied by the battery must drop
03:26	over the sum of the two resistors , part over
03:29	the first and the remainder over the second . The
03:32	second property talks about current current flows through each resistor
03:36	, one after the other . That means the same
03:39	current that flows through the first resistor must flow through
03:41	the second . The total resistance in a series circuit
03:45	is the sum of the two resistance is , let's
03:48	return to our water experiments . We can better understand
03:50	potential and current in a series circuit , water starts
03:53	in the funnel at the top and must travel through
03:55	each of the loops on the way to the bottom
03:58	, one after the other notice that there's two distinct
04:02	potential drops in the circuit , from 28 to 14
04:05	inches across the first set of loops and from 14
04:08	to 0 inches across the second set . For a
04:11	total potential drop of 28 inches , 100 ml of
04:15	water starts at the top And it all drains to
04:17	the flask at the bottom in 25 seconds . A
04:20	current of four ml/s . The water experiences more resistance
04:25	in the circuit . Therefore , the current is smaller
04:30	. In our series electric circuit , a nine volt
04:33	battery supplies current that flows through two resistors each of
04:36	1500 homes . To measure the current in the circuit
04:39	, I broke the circuit here and place the meter
04:41	within it . Our meter reads three million amps .
04:45	This is the current within our circuit and it's the
04:47	same regardless of where we measure it because there's only
04:50	one path for the current to take . I've rearranged
04:53	the meters to measure potential in the series circuit .
04:56	This meter reads potential drop across resistor one , which
05:00	is about 4.5V . This meter reaches potential drop across
05:05	resistor to which is also 4.5V Add these two values
05:09	together and you get the battery potential 9V . The
05:13	diagram on the left represents a parallel circuit where a
05:16	battery supplies current that flows through two resistors placed side
05:19	by side . The parallel circuit properties are on the
05:22	right . The first talks about current . The current
05:25	supply by the battery has a choice as it splits
05:28	between a path through are one and the path through
05:31	our two . The second property talks about potential .
05:35	The potential supply by the battery is the same potential
05:38	that drops across our one and is also the same
05:41	potential that drops across our two . The total resistance
05:45	in a parallel circuit is given by this expression and
05:48	is less than that is seen in a series circuit
05:51	. Let's return to our water experiment one more time
05:53	. So we can better understand potential and current .
05:55	In a parallel circuit , water starts in the funnel
05:58	at the top and can take one of two paths
06:00	to the flasks at the bottom , either through the
06:02	left loops or the right loops . Notice that the
06:05	potential drop is 18" , regardless of which path the
06:08	water takes . We start with 100 mL of water
06:12	at the top and approximately 50 ml ends up in
06:15	each of the flask at the bottom . It takes
06:17	about 12 seconds . This means that the current in
06:21	each path is about four mm/s , Adding these together
06:25	. We get eight per second for a total current
06:30	. You should expect the current to be higher in
06:32	a parallel circuit . This is because there are two
06:35	distinct paths for the water to flow . Therefore the
06:38	water sees less resistance and is able to flow faster
06:41	through the circuit . In our parallel electric circuit ,
06:44	a nine volt battery supplies current that flows through to
06:47	1500 ohm resistors placed side by side to measure the
06:51	total current in the circuit . I broke it here
06:54	. The meter reads 12 million amps . How to
06:56	measure the current flowing through our two , I broke
06:59	the circuit here . This current is six million amps
07:02	, which is less than the total because the remainder
07:05	must flow through our one . I've rearranged the meters
07:09	to measure potential in a parallel circuit . This meter
07:13	measures the potential drop across resistor one And it's about
07:16	9V . This meter reads a potential dropped across R
07:21	two is also 9V . Notice that the potential drop
07:25	across both resistors and the parallel circuit is equal to
07:28	that of the battery . Now it's your job to
07:33	keep exploring challenge yourself by investigating voltage in current .
07:36	More complicated circuits , like if you change the values
07:39	of resistance or if you add a third resistor or
07:42	even if you can buy in series and parallel circuits
07:44	to form a big mega circuit .

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