Lesson video

Hi, I'm Mrs. Hudson, and today we're going to be learning about electric current.

This is a Key Stage 3 science lesson, and it comes under the unit called Series Circuits.

Let's get going.

The outcome of today's lesson is: I can describe how a cell causes current in a circuit and explain the movement of electrons.

There will be some words used frequently throughout today's lesson, and those keywords are: electrical cell, charge, electron, and electric current.

So let's have a look at what those words mean.

An electrical cell is a component that uses a chemical reaction to make electric charge flow around a circuit.

Objects can have an electrical charge that is positive or negative.

If there is no charge, they are neutral.

Electrons are the charges in conductors that flow to cause an electric current.

And, finally, electric current is the flow of electric charge in a circuit.

If you want to make note of those keywords, then please pause the video and then press Play again ready for me to continue.

Today's lesson on electric current is going to be split into two parts.

In the first part of the lesson, we're going to be looking at what is an electrical cell, and then we're going to move on to look at what is current.

But let's get going with the first part of the lesson: what is an electrical cell? An electrical cell has a plus or positive end, and we can see here there's a picture of an electrical cell, and we can see that the positive end has been labeled.

Now, what you might notice on this electrical cell is that the positive end has a plus sign and also it has a sort of copper-colored end.

This is a drawing of an electrical cell.

And, again, we can see that the positive end, which is copper-colored, has the positive sign on it.

But also you should notice that there's a protruding bit of metal coming out of the positive end, and this is there so it can make good connections.

The other end of the electrical cell is negative, and the ends are called terminals.

So there's a positive terminal and a negative terminal in every electrical cell.

The positive terminal is always labeled, but sometimes the negative terminal may not be labeled.

Let's quickly check our understanding of that so far.

Which cell has a terminal labeled with the correct symbol: A, B, or C? Now, this question's a little bit trickier than it first looks, so hopefully here you got B.

The reason why A is wrong is because the positive terminal has been labeled with a negative sign, and we know that the positive terminal is the terminal that's the copper color, and also it has that protruding bit of metal.

And the reason why C is wrong is because they've put a positive sign at the negative terminal of that electrical cell.

So well done if you recognized that.

Chemical reactions inside a cell make the terminals positive and negative.

So we can see a diagram here of an electrical cell, and then there's a label that's saying that there are chemicals that react inside of that electrical cell.

And that is what makes the positive terminal and the negative terminal.

These terminals push charges round a circuit.

More than one cell connected together makes a battery of cells, commonly called a battery.

And I think in everyday life we use the term battery much more than a cell, but sometimes when we use the word battery, we actually mean cell.

So here this diagram is showing you one cell that's got a positive and a negative terminal.

But if we added in another cell, we've now got two cells that make up a battery.

So that diagram now is a battery of two cells.

There are many different cells and batteries used for different purposes.

And we can see here there's a selection of different batteries and cells, and let's have a look in a bit more detail of what they might be.

So the largest image here is showing you a power bank.

This is a battery that's designed to be portable that you would take around to help recharge electrical devices when you are on the move.

You've also got a rechargeable cell.

So the silver and the green cells there are both rechargeable.

And then you've also got an alkaline cell which is not rechargeable.

And then at the bottom there's a torch battery.

And then above that you've got a watch cell.

And you can see again there that, if you look closely, the positive terminal is facing up in the picture.

And then you've got a camera battery as well.

A mobile phone contains a large rechargeable battery, and you can see that labeled in the image here.

The phone cannot work if the battery does not push current through the circuits.

So if you remove the battery from the phone, the phone will not switch on at all.

Electric cars have large batteries that must be recharged regularly, and you can see the image here of an electric car which is plugged in, and that charger will be linked to an electrical output.

And I'm sure if you drive around near your homes and schools that you've seen electric cars and potentially seen them plugged in.

Let's check our understanding of that so far.

Which of the following statements about cells and batteries is correct? A, they are all rechargeable? B, they can come in different shapes and sizes? C, they use fossil fuels to generate electricity? Or, D, they have a positive and negative and a neutral terminal? Now, hopefully for this one we recognize that B was the correct answer.

A is wrong because you can get some batteries like alkaline batteries that are not rechargeable.

C is wrong because batteries and cells don't use fossil fuels to generate electricity.

They contain chemicals.

And D is wrong because, yes, cells and batteries have a positive and negative terminal, but they don't have a neutral terminal.

So well done if you've got that right.

A simple cell can be made using two different metals such as zinc and copper placed in a lemon.

The acidic juice in the lemon reacts with the metals, causing a charge to flow around the circuit.

And we can see in this diagram here that we've got a lemon that's got two different metals such as zinc and copper placed inside, and they're connected to wires which are then connected to a voltmeter, which is showing you that there's a voltage.

Now, it's really important if you're trying to use lemons to set up a simple cell that the metals you use have different reactivities because this is then how the current is allowed to flow around the circuit.

When putting cells together, we should ensure that cells are connected so they are aligned in the same direction.

So we can see we've got a cell here with a positive and a negative terminal.

And if we were going to introduce another cell to make a battery, you would need to make sure that the positive terminal of the next cell is aligned to the negative terminal of the previous cell.

And, again, if we added in a third battery, the positive terminal would need to come in first again.

Positive terminals should connect to negative ones, and all of the cells should be the same type.

Now, as well, highlighting on this page, if we remember that the circuit symbol for a cell is a longer, thinner line with a gap between the next shorter, wider line.

And the long, thin line is showing you the positive terminal of the cell, and the shorter, wider line is showing you the negative terminal.

Let's check our understanding.

Which of the following is a symbol for three cells correctly connected together? Is it A, B, or C? So hopefully here we recognize that A was the only symbol that was correctly showing three cells connected together.

B is wrong because we can see that the second cell has got the negative terminal connected to the negative terminal of the first cell, which is incorrect.

And C is wrong because there is no positive terminal drawn for the second cell in the sequence.

So well done if you managed to get that right.

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

Some pupils are trying to light a lamp as brightly as possible.

They have a variety of cells and batteries, which we can see in the picture below.

Explain how they should do this safely.

So this task is going to draw on lots of the different things we've spoken about in the first part of this lesson.

I'm sure you're going to do a really great job if you pause the video, give it your best go, and then press Play ready for me to go through the answers.

Let's see how we did with that one then.

So, first of all, you want to sort the cells and batteries into each type.

Because, remember, we only use batteries of the same type together.

And then, secondly, pick the type that has the most cells and connect them end to end, pointing in the same direction.

You might be more specific there and say that you need to connect the positive terminal to the negative terminal of the next battery.

Then, number three, connect them to the lamp.

And, number four, repeat these steps with each type of cell or battery to see which set makes the lamp shine the brightest.

Fantastic job if you've got some of those ideas into your answer 'cause that was quite a tricky question.

If you want to pause the video to add anything into your answer, then please do, but otherwise we're gonna get going with the second part of today's lesson.

Well done, we've got through the first part of the lesson on what is an electrical cell.

So let's look in a little bit more detail now about what is current.

A cell pushes negative charges out of the negative terminal and pulls them into the positive terminal.

And we can see this diagram here is trying to show you that concept.

So if you focus your attention to the cell at the top of the circuit and remember the black side of that cell is showing you the negative terminal.

And you can see there's negative charge being pushed out of the negative terminal of that cell, and it's being pushed around the wires of the circuit.

And eventually those negative charges will go into the lamp, where energy will be transferred as light, and then the electrons get pulled back into the positive end of the terminal.

So just a reminder there: the cell pushes negative charges out of the negative terminal and pulls them back into the positive terminal.

Now, if you look closely in the wires, you'll see that the negative charge is represented by these blue circles with a negative symbol within them.

These charges are called electrons.

The cell pushes electrons out of the negative side of the terminal, and then the electrons are pulled back into the positive side of the cell.

It's really important to know that electrons aren't actually circles of blue.

That is just used to help you understand the concept of the flow of electrons.

Let's check our understanding of that.

Which of the following statements about a cell is correct? A, positive charge is pulled into the negative terminal? B, negative charge is pulled into the negative terminal? C, negative charge is pushed out of the negative terminal? Or, D, positive charge is pushed out of the negative terminal? Now, these answers are all quite similar, so think carefully about which one is correct.

So this one was a bit tricky, but the answer is C: negative charge is pushed out of the negative terminal.

The other answers there were just put in as distractors to try and confuse you.

So well done if you managed to get C right.

Now let's have a look at another question: which diagram most accurately shows the direction of electrical current in this cell when the lamp is lit? Is it A, is it B, or is it C? And you need to be looking at the arrows here very carefully.

Now, the answer to this question is B, so well done if you've got that right.

A is wrong because it is showing the flow of electrons going around the circuit, but it only has one arrow going into the component, and there isn't another arrow showing the flow of electrons from the lamp back to the battery.

B is correct because it shows both the electrons moving out of the battery and then from the lamp back into the battery.

And C is incorrect because it's showing electrons flowing in different directions, and the arrow from the lamp to the battery needs to be the other way around.

So well done if you got that right.

Electrons are too small to see even with the best optical microscopes.

So this image here is showing you the structure of an atom that has electrons within it.

So we can see here that the electrons in this diagram are represented by blue circles.

But, again, that's just a representation of a model.

The electrons aren't actually blue negative spheres.

This is another way of showing electrons in a metal.

So we can see that the copper-colored circles are representing metal atoms and then the electrons are these little blue spheres.

And you can see that the electrons are dotted randomly around the atoms and they're free to move in a metal, which is why metals are very good conductors of electricity.

So the electrons can flow easily between the metal atoms, making metals good conductors.

Let's check our understanding.

Which two of the following statements about electrons are correct? A, they are negative charges? B, they are blue? C, they are tiny? Or, D, they are only found in wires? So for this you should have got: A, they are negative and, C, they are tiny.

Electrons are not blue, and electrons are also not only found in wires because we said that they were found in metals.

So well done if you got those two questions right.

So if the circuit is broken, then the electrons cannot flow across the gap.

So here we can see a diagram which is showing you a broken electrical circuit where there's a gap between the wires.

And it's really important to note that, even though the electrons are not moving, the electrons are still present within the cell, the wires, and the bulb.

And we can see this on this diagram.

The electrons are still inside the cell, they're inside the wire, and they're inside the bulb.

But because the circuit is broken, the electrons are not flowing, and the reason why the bulb won't light is because the electrons cannot flow across the gap between the wires.

Let's check our understanding of that so far.

Where in a broken circuit are there no electrons available to flow? A, the wires? B, the filament bulb? C, the cell? Or, D, the gap? Hopefully you remembered that this was D, the gap.

There are electrons present in the wires, the filament bulb, and the cell.

It's just that they will not move if the circuit is broken.

And as soon as the circuit is complete, those electrons will begin to flow.

A flow of charges, electrons, is called an electric current.

And we can see here there's a wire that's got electrons in it, and those electrons are flowing, which means there will be a current within this wire.

This is similar to the current of water in a river, and here the water is representing the electrons which are flowing in the wire.

So, in a river, water flows down a river in the same way that electrons flow through a wire.

Let's see if we've understood that.

A teacher uses a model of a river to explain how current flows.

What does the model use to represent charge? A, the water in the river? B, the speed of the river? Or, C, the ripples on the water surface? Now, this is A, the water in the river.

So well done if you remembered that.

When electrons leave the cell, the same number enter at the other terminal of the cell.

So if we've got electrons being pushed out of the negative terminal of the cell, the same number of electrons will enter at the positive terminal of the cell.

For every electron that enters the bulb, another leaves.

The current in this series circuit is the same here as it is here, as it is here, as it is here, and here.

The current is the same at any point in a series circuit.

Let's check our understanding of that.

Which of the following statements is correct when the lamp is bright? A, the current is lower after passing through the lamp? B, the current is higher at the negative side of the circuit? C, the current in the cell is higher than in the lamp? Or, D, the current in the cell, lamp, and wires is the same? Well done here if you've got D as the correct answer.

Current is the same at any point in a series circuit.

When the switch is turned on, current flows and the bulb immediately lights.

So if you focus your attention onto the yellow box of this diagram, you can see that the switch is being turned on and off.

When it is turned off, current stops flowing, and the bulb immediately goes off.

And when the switch is turned on, the current will immediately start flowing back, and the light will immediately turn on.

Even when the circuit has very long wires, the bulb lights and goes off immediately when switched on or off.

And it's the same concept.

As soon as the switch is turned off, then the electrons will stop flowing and current will stop flowing.

And then as soon as the switch is turned on, the electrons will immediately begin to move and the current will flow, which causes the light to turn on immediately.

You'll notice this is the same with the lights in your home.

So as soon as you flip the switch, the lights will come on, and as soon as you switch off the lights, the lights will immediately go out.

So here we've got a circuit which has got a switch, three lamps, and a cell, and when the switch is closed, so the circuit is complete, all three bulbs come on at the same time with the same brightness.

The individual electrons only move a few millimeters per second, but the bulbs all light immediately and with the same brightness.

Let's check our understanding.

The switch is closed in this circuit and the lamps light.

Which statement is true about how they light? A, Lamp 1 lights first? B, they all light up at the same time? C, Lamp 3 lights first? Or, D, lamps 1 and 3 light before Lamp 2? So hopefully here we recognized that B was the right answer: they all light up at the same time.

And this is because, as soon as the switch is closed, the electrons which are within the circuit, the wires, the cell, and the bulbs, will all immediately start flowing, and the current is exactly the same at every point in the circuit.

So well done if you got that right.

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

The switch in this circuit is closed to turn the lamps on.

All of the bulbs in the lamps are identical.

Question 1: describe how the bulbs light, including the timing and the brightness.

And, number two, explain why the bulbs light the way you described.

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

Give it your best go and think really hard about the things that we've been talking about this lesson and then press Play when you're ready for me to go through the answers.

Let's see how we did with Task B.

So for Question 1, the bulbs will all light at the same time and will have the same brightness.

And then for number two, explaining why that's the case, the bulbs light at the same time because there are charges, also known as electrons, throughout the wires.

The charges all start moving together when the switch is closed.

The bulbs will each have the same brightness because the same current flows through all of them.

Really, really great job today, particularly if you managed to get lots of information into that second part of Task B.

If you need to pause the video to add anything into your answer to make it a little bit better or correct anything, then please do, but we're going to move on now to summarize everything that we've learned today.

So today we've been learning about electric current, and we started off the lesson by saying an electrical cell uses chemical reactions to make charge flow in a circuit.

And we said that an electrical cell has a positive and a negative terminal, and we can see an image of an electrical cell there with the positive terminal that has the protruding metal and then the negative terminal, which sometimes isn't labeled.

The components in a circuit contain many negative charges called electrons.

When electrons flow in a circuit, it is called an electric current.

The current is the same all around the circuit, causing all components to switch on or off at the same time.

We also said, if you had multiple lamps within a circuit, that they would all shine with the same brightness because the current is the same at any point in the series circuit.

Fantastic job on today's lesson, well done.

I've really enjoyed it, I hope you have too, and I look forward to seeing you next time.