Lesson video

Hi, I'm Mrs. Hudson.

And today, we're going to be looking at a lesson called Making Parallel Circuits.

This is a key stage three science lesson, and it comes in the unit called Resistance and Parallel Circuits.

So let's get going.

The outcome of today's lesson is, I can use circuit diagrams to build parallel circuits and draw circuit diagrams of parallel circuits.

So we're going to be looking at parallel circuits, we're gonna build some parallel circuits.

And then, finally, we are going to draw some parallel circuits.

There will be some words that are used frequently in today's lesson, and those are the keywords.

And today, they are series circuit, complete circuit, parallel circuit, and circuit diagram.

So let's look at what each of those words mean.

A series circuit is an electric circuit with one complete loop from one end of a cell or battery to the other end.

A complete circuit is a circuit that has no gaps, allowing electricity to flow continuously around the circuit.

A parallel circuit is an electric circuit with more than one complete loop from one end of a cell or battery to the other end.

And finally, a circuit diagram is a simple and clear way of showing the setup and components in an electrical circuit.

If you want to pause the video now to make a note of those keywords, then feel free to, and then press Play when you're ready to continue.

Today's lesson will be split up into three different parts.

And in the first part, we're going to be looking at parallel circuits and the theory of parallel circuits.

Then in the second part, we're going to be building some parallel circuits.

And then in the final part of today's lesson, we are going to be drawing some parallel circuit diagrams. But let's get going, first of all, with just talking about some parallel circuits.

This picture here is showing you a series circuit.

There is only one complete loop from one end of the cell round to the other end, which we can see here, represented by the purple line.

So the current is being pushed by the cell, and it's traveling from one end of the cell to the other end in one complete loop.

Because there is only one loop in a series circuit, there are no junctions.

Let's check our understanding of that.

Which of the following statements about a series circuit are correct, A, there is a single loop, B, there are no junctions, and C, the loop starts and ends at the same point of the cell or battery? Select the correct answers.

Hopefully, here, we went for A.

That is correct.

A series circuit does just contain one single loop.

And also B is correct, because there are no junctions as well.

So great job if you managed to get those right.

Well done.

C is not correct because the loop doesn't start at the same point of the cell or battery.

The loop starts at one end of the battery, and then connects round to the other end of that cell or battery.

So well done if you managed to recognize that that is incorrect.

Now, let's look at a parallel circuit.

This picture here is showing you a parallel circuit.

And if you look at it, we can see that there is more than one loop from the cell.

And this purple line here, first of all, is showing you the first loop, which we can see is going from one end of the cell to the other end of the cell.

But notice now that there is a second loop, which we can see here is going from one end of the cell around to the second lamp, and then up again, back to meet the cell.

So a parallel circuit has more than one loop.

There is a junction where the current splits in the two loops.

So this is the same circuit as before, but we can see here that the wire comes out of the cell, but then there's the junction.

And here, at the junction, the current can split because there's two different paths that it can go down.

Then there is a second junction where the current from the two loops is going to join back up.

So we need to know that parallel circuit contains more than one loop, and there are also junctions where the current can split in a parallel circuit.

These circuits work the same way.

They are effectively the same circuit.

And we can see that there are two parallel circuits shown here, each containing a cell, two lamps, and a switch.

We can see that there is a junction where the current splits and there is another junction where the current is going to join back up.

And these two circuits look like they might be different, but actually, from the cell, there is a single loop that's containing a lamp and a switch, and then there is a second loop that also contains the other lamp.

So they are still the same circuit.

Let's check our understanding of that so far.

Which of the following statements about current at junction are correct, A, at a junction, current can split, B, at a junction, current goes through only one loop, or C, at a junction, current can join up? Hopefully, here, we recognized that two of these statements were actually correct.

The first correct statement is A, at a junction, current can split.

And then also C is correct, because at a junction, current can join up.

So well done if you managed to get those two correct.

B is not a correct statement, because at a junction, current is going to go through both of the loops rather than just the one loop.

So well done if you recognized that B was incorrect.

The circuits that we've just been looking at can also be shown with circuit diagrams. So if you look at the top left-hand circuit here, which is containing a cell, two lamps, and a switch, and the two lamps are in two different loops, so it's a parallel circuit.

If we were going to represent that with a circuit diagram, it would look like this.

So we can see the cell, you can see there's a first loop, which contains the lamp, and then that goes back up to the switch, which then goes back into the cell, and then we can see the second loop, which contains the other lamp.

Now, if we were going to represent the circuit on the right-hand side in a circuit diagram, the only difference here is that the cell is in the middle, is in between, and you've got a lamp both above and below the cell.

So you would represent that circuit with this diagram here.

So the cell is in the middle, and then you can see the switch is next to it.

And then you've got a lamp, which is going above the cell in one loop, and then there's another lamp below the cell in one loop.

These circuit diagrams are for the same circuit.

So if we look here, we've got the same diagram that we've just looked at, and they both have got junctions.

So they've both got a junction on the left-hand side, and they've both got a junction on the right-hand side.

Here, we've got the same circuit diagrams again, and these circuit diagrams are for the same circuit, even though they look slightly different.

And another way we can tell that they're the same circuit is that each lamp is lit by a separate loop.

So if you focus your eyes now on the purple line that's going to come up, it's going to show you one of the loops within each of the circuits.

So first of all, if we look at the left-hand circuit, there is one loop which has a cell, the current goes through one of the lamps, and then back up through the switch, back to the cell.

And then we can see on the right-hand circuit that there's a cell there, and one of the loops goes through the lamp, and then back through the switch, up to the cell again.

Then now, we're gonna show you the second loop.

So on the top, there's also a loop going from the cell down to the bottom, lamp up, and then back through the switch.

And then on the right-hand side diagram, we've got the cell, the loop is going up through the lamp, and then back down through the switch, back into the cell.

So each lamp is lit by a separate loop within both of these circuits.

Even though they look different, they are actually the same circuit.

Let's check our understanding of that.

And remember that each lamp is going to be lit by one of the loops.

So which one of these circuits shown is different from the others, A, B, or C? Now, if you need to pause the video now to have a look more carefully, then please do, and then come back, ready for me to give you the answer.

Now, hopefully, here, we recognized that A was the circuit that's different from the others.

Now, the reason that A is different is because if you go from the cell round into the two loops, in A, the first loop is going to contain the lamp, and then if you went across to the switch, and then up, back to the cell, it would have one lamp in it.

But if then you went to do the second loop, the second loop will also contain the first lamp that's on the top line, as well as the bottom lamp.

So the first lamp is included in both of the loops.

Whereas in circuits B and C, each loop only lights up one individual lamp.

So really well done if you managed to recognize that.

Great job.

In parallel circuits, it is where the junctions are that is important.

So if we look here, we've got two diagrams of parallel circuits, each containing a cell, two lamps, and a switch, and there's a lamp in each loop here.

And we can also see that there are junctions which are circled in purple, and we've got junctions to the left and to the right.

These circuits are the same, even though the components are in different places.

So it's where the junctions are that are important, not where the components are.

Let's check our understanding of that.

Which of the following is the most important when trying to determine if parallel circuits are the same, A, the position of components, B, the position of junctions, or C, the position of wires? This is B, it's the position of junctions that's important.

So well done if you've got that right.

Great job.

We're ready now to move on to task A of the lesson.

And your job is to look at these four different circuits labeled A, B, C, and D, and you are going to identify which of the circuits work the same way, and you need to explain your answers.

So you need to be looking at where the junctions are, if the circuit's a series or parallel.

I'm sure you're gonna do a really fantastic job of this.

Pause the video, give it your best go, and then press Play when you are ready for me to go through the answers.

Let's see how we did.

So, hopefully, you recognized that circuits A, C, and D are the same parallel circuits, as they have junctions leading to two separate loops.

The two loops in each circuit each have one lamp, so they are the same.

Therefore circuits A, C, and D will work the same way, even though the lamps and wire positions are different.

Circuit B is a series circuit which is different from the others.

So fantastic job if you managed to recognize that A, C, and D were the same and B is a series circuit.

If you need to add in any extra detail to your answer, then please pause the video, do that, and then come back, ready to carry on with the rest of the lesson.

Great job with the first part of the lesson.

Let's have a look now at how we are going to build parallel circuits.

When building a parallel circuit, it is best to follow a set of steps.

So we can see here that we've got a parallel circuit which contains a cell, and then two loops each containing a lamp, and then there's a switch as well.

What you would need to do if you're going to build this circuit would be to collect the equipment needed, which we can see from the circuit diagram.

You need a cell, you need a switch, you need two lamps, and you need some leads, which are the wires.

Let's check our understanding of that first.

Which of the circuit symbols shown represents a lamp, is it A, B, or C? Hopefully, here, we went for A.

Well done if you got that right.

B is a cell, and C is an ammeter.

Once we've got all of our equipment for that circuit, we need to identify a single loop within the circuit.

So, for example, that would be one single loop within this circuit here.

And then starting at one point in the loop, connect up the components one by one, going in the same direction until the loop is complete.

So for this loop, we would start with a cell, for example, and then you would use a wire to connect that to a lamp, then use another wire to connect that up to a switch.

And then the switch would need to be connected back to the cell with a different wire.

So let's look at building that first loop.

There's our cell.

We're going to use a wire to connect that to the lamp.

We're then going to use another wire, connect that to a switch, and then use the final wire to connect to the switch back up to the same cell.

And we can see that that's one complete first loop.

So we can see that the current is going to flow around that circuit from the cell, through the lamp, through the switch, and then back up to the cell.

On its own, this is a series circuit with one loop, but we're now going to make this into a parallel circuit.

So we're going to find the first junction on the first loop, which we can see is circled in green here.

And then find the next loop on the diagram, which contains, in this circuit, another lamp, and then we're gonna connect the components up.

So there is our junction, we're going to use a wire, connect that up to the next lamp, and then use a wire to connect it back up to the second junction.

And we can see there, that's our second loop.

And when the current gets to the junction, it's going to split, some of it's gonna go through the first loop, and then some of it is going to go through the second loop, and it will join back up again at the second junction.

It's also possible to start with the lower loop.

So you could start by building that loop there, which is in green.

Now, this would consist of a cell, with a wire connected to a lamp, and then another wire up to a switch.

And then, finally, connecting that switch back up to the cell with another wire.

We would then finish with the other loop.

So, here, we would add in another wire, connected to a lamp, and then a wire to connect back up to that junction.

So that's the same circuit.

We've got two junctions.

We just started with the lower loop this time.

You can start building at any point in the circuit, as long as each loop is completed in turn.

So, here, we can see, you could start at the cell, you could start at the switch, you could start with the lamp, or you could start with the other lamp.

As long as you make sure that each loop is completed in turn, it doesn't matter which component you start with.

Let's check our understanding of that.

Which of the following steps must you follow when building a parallel circuit, A, start at the battery or cell, B, complete each loop, or C, always go clockwise? This is B.

You must complete each loop before starting the next one.

A is not correct because it doesn't matter if you start with a cell or the battery.

I mean, it is a good place to start as a starting point, but you don't have to start with a cell or battery.

And also C's incorrect because you don't have to go clockwise.

As long as you complete each loop, then that's absolutely fine.

Well done if you've got that right.

We're ready now to move on to task B of the lesson.

And this is more of a practical task.

And you are going to build the following circuits using the circuit diagrams below.

So you can see, there are three circuits numbered one, two, and three, and you need to go away and build each circuit, making sure that you build each loop individually, starting with one loop first.

I'm sure you're gonna do a really good job and have lots of fun doing this.

Pause the video, and then press Play when you are ready for me to go through the answers.

Let's see how we did.

These are just some visual images of what your circuits might have looked like, but if you look at the first one, you can see that we've got the cell, there's a single loop with one lamp in it going up to the switch, and then the second loop has got two lamps within it, which then joins back up at the junction.

Then for circuit two, you can see that there's a lamp immediately to the left of the cell.

The first loop then contains two more lamps, the switch, and goes back to the cell.

And then in the second loop, you've got an individual lamp.

And then in circuit three, you've got the first loop, which contains two lamps.

And then there's another lamp going back up after the junction, and then the bottom loop has got the switch within it and another lamp.

So well done if you managed to make all of those circuits.

Really great job.

You've done really well so far in the lesson.

We're going to move on to the final part of today's lesson now, which is drawing parallel circuit diagrams. When drawing a circuit, again, it is best to look for junctions and loops.

So we can see we've got a circuit here, and we can see the first loop contains a cell, a lamp, and a switch, and there are two junctions within the circuit.

And then the second loop contains two lamps, which then joins back up at the junction before the wire gets to the switch.

If you wanted to draw this parallel circuit, first of all, you're going to start by drawing the first loop, and we're going to use the circuit diagram symbols within our diagram.

And make sure, when you're doing these, that you are using a ruler for the wire, so they're nice and straight, that we're drawing everything in pencil, and that we're using the correct circuit component symbols.

So that first loop here contains a cell, which has a symbol with a longer line and a slightly shorter line, that's gonna come round, and then we're gonna have the first lamp drawn.

Remember that the wire lines do not go through the lamp symbol.

And then that lamp is gonna go up and connect to the switch, and the switch is going to connect back up into the cell with a wire as well.

So that's our first loop drawn.

We're then going to look at the second loop and add that in that second loop.

So we can see, from the junction, we draw a line down, a straight line down, and look at the components within that second loop, which is two lamps.

We're going to draw those two lamps into the second loop.

And then with a wire, connect that back up to the second junction, which occurs before the switch.

Circuit diagrams should be drawn one loop at a time.

Correct symbols should always be used.

So, for example, there, you've got the cell and the switch, and you need to make sure you are using the correct symbols.

Horizontal and vertical lines for the wire should be drawn with a ruler and in pencil.

And then make sure there are no tiny gaps in the lines, especially at corners and at junctions, because that would show that the circuit was incomplete, and that would mean that current couldn't flow around the circuit.

Let's check our understanding of that.

So we can see here that there's a circuit diagram that's been drawn.

And you need to identify the errors within the circuit diagram shown.

So have a look at that circuit now, and then I'm gonna read out the options for what the errors could be.

A, the cell is the wrong way round, B, there is a tiny gap in the middle branch, C, there is a wire drawn through the ammeter.

So which of those are errors within that circuit diagram? So, hopefully, here, we identify two errors.

B is an error.

There is a tiny gap in the middle branch.

And I know that is only very tiny, but those lines are not connected, which would mean the wires would not be connected, and therefore electricity could not flow.

So all the lines need to be connected.

C is also the correct answer, because the ammeter does have a wire line drawn through it, and it shouldn't have the wire line drawn through it.

So well done if you recognized that.

A is not correct in this one because the cell isn't drawn the wrong way round.

So well done if you've got B and C.

Great job.

We're ready now to move on to the final task of today's lesson, task C.

And your job is to look at these images of some circuits, and you are going to draw circuit diagrams for the circuits below.

So circuit one, circuit two, and circuit three.

So look really closely at each individual loop, look at where the junctions are, and make sure that you follow the rules that we just spoke about, and complete one loop at a time.

I'm sure you're gonna do a really great job.

Pause the video, and then press Play when you're ready for me to go through the answers.

Let's see how we did.

So your diagram should be similar to these.

So if you have a close look at those images, you should have very similar diagrams to that, and really pay attention to where your junctions are, and the components within each loop.

It's really important that the junctions are in the right place and the components are in the same loop.

Fantastic job on today's lesson.

If you need to pause the video to correct any of those, or add any detail into your answer, then please do.

But if not, I'm gonna summarize everything that we've learned so far today.

So, today, we've been looking at making parallel circuits.

And we started off by saying a parallel circuit is a circuit with more than one complete loop from one end of a cell or battery to another end.

We said that junctions in a parallel circuit lead into additional loops.

When building a parallel circuit, it is best to build each loop one at a time, looking out for where those junctions are.

The same parallel circuit can look very different because the components can be in different places, but the sequence of connections to components is important, and where those junctions are as well.

And finally, we said use loops and junctions when drawing parallel circuits, and make sure that you draw circuit diagrams with the correct component symbols, and that we're using a ruler and a pencil, and draw each loop one at a time.

I really enjoyed today's lesson, I hope you have too.

And I look forward to seeing you next time.