Hello, scientists.

My name is Mr. Wilshire, and today, we're going to be troubleshooting some problems with circuits.

So let's dive in and hopefully light some bulbs in those brains.

Our outcome today is to solve some problems and improve simple circuits.

Here are some key words for our lesson today.

I'm going to say them, and I'd like you to repeat them after me.

My first key word is circuit.

Great job, the next one is complete.

Excellent, next incomplete.

Excellent, and next up connector.

Well done, and last one, electrician.

Very good.

Now here are the definitions for some of those key words, so don't worry if you're not too sure what some of them mean.

You can pause the video here if you like, and have a quick read through so you are sure you know what they mean.

As we go through the lesson, they're going to pop up, so hopefully you'll get a good idea as to what they mean and how we can use them.

Let's crack on then.

The first part of our lesson today is called troubleshooting incomplete circuits.

Now, sometimes circuits don't work, and when this happens, we need to be able to work out why and solve the problem.

This is known as troubleshooting.

Sometimes, they don't work because the components haven't been connected correctly.

This often means that a circuit is incomplete.

Remember, a circuit is a continuous flow of electricity, isn't it? It needs to work a bit like a circle.

The electricity needs to be able to flow from one side to the other, and then come back again.

If it's incomplete, the electricity can't flow.

Andeep and Sam here have built some circuits, but they don't work.

I can see a wire and a bulb.

I can see a cell and some wires with crocodile clips.

They know that all the components work, so why won't the bulb light up? Pause a video here and have a quick chat.

Come back when you are ready.

I wonder what you discussed and why you think that the bulb won't light.

If you look very closely, you'll see that the circuit is incomplete.

It's because the wire linking the bulb to the positive end of the cell is not connected.

Ah, I can see there now that, yes, one of the crocodile clips has come off of the bulb.

That's one the reasons why circuits don't work, so I wonder why this bulb won't light up.

All the wires are connected now.

Have a discussion, pause the video, and continue when you are ready.

Hmm, this circuit is also incomplete, but how, if all the wires are connected? Oh, there's a wire joining the bulb back to the cell, but both wires, ah, they're both attached to the same end of the cell.

That means electricity can't flow.

Remember that a cell is going to provide the electricity for the circuit, and that needs to be included in it as well so it can form part of that big circle.

One wire needs to be attached to the positive end and one wire needs to be attached to the negative end of the cell.

And then as you can see there, the bulb is able to light up, and we can see again.

Andeep's older brother has a tip for testing whether a circuit is complete.

Hmm, here's Andeep's older brother.

Use your finger to trace the circuit from one point and see if you can go all the way around through all the components and end up back where you started with no gaps.

That's really good advice, yes.

Remember, the electricity needs to flow all the way through the circuit from one side of the component to the other.

So both wires are coming out of one side.

The electricity can't flow, can it? Andeep and Sam both understand.

Well, that's good.

Andeep says, "On this circuit, "you can't go all the way round." Look, there's a gap, of course.

Sam says, "On this circuit, you can go round in a loop, "but you can't go through the cell." Oh yes, that part there is where the wires are all connected to one end of the battery.

Let's stop and think.

What is the name for a circuit where all the components are not connected correctly in a loop, or where there is a break in the loop? Pause the video here, have a discussion and restart when you're ready.

The name for a circuit which isn't making a loop is an incomplete circuit.

Let's stop and think again.

How should a cell or battery be connected to a circuit? Have a read of the statements here and decide which ones are correct.

Pause the video, and restart when you're ready.

A cell can be connected to a circuit through the wires.

One wire needs to be attached to the positive end and one to the negative end of the cell so electricity can flow through it.

Here's your first task.

Not all of these circuits are complete.

So for each circuit, have a think.

Predict whether you think it will work.

Build it to test your prediction.

Hmm, so we've got number one there.

We've got a cell and a bulb.

Number two, a cell and a motor.

Three is a cell and a bulb again.

Four is a cell and a buzzer.

Five is a cell and another motor.

And six is a cell and one last bulb.

Well, have a discussion about what you can see there.

Have a go.

Have a go building some of these circuits as well if you've got the components in your school.

Pause the video, and restart for the answers.

So for each circuit, you had to predict whether you think it would work and then have a go building it as well.

Andeep says, "I predict "that the buzzer will not make a sound "because there is only one wire on one side "connecting it to the cell." Yeah, he's right, isn't he? It needs two wires there.

Sam says that she, "Predicts that this bulb will light "because the components are in a loop "so she can trace her finger all the way around." All that's using the advice from Andeep's brother, isn't it? Here are the circuits that are correct.

I've ticked the ones with a green tick to show the ones that work and a red cross showing the ones that don't work.

I wonder if your predictions were correct.

Take a moment to pause and check your answers.

Okay, let's get into the next part of our lesson.

Troubleshooting components.

Andeep and Sam have built this circuit, but the buzzer won't buzz.

Oh, that's annoying.

They've done a good job there as well.

I can see it goes in a circle.

I can trace my finger all the way around, and they've traced their circuit as well, just to make sure that it was a complete loop.

Sometimes, a circuit can look correct, but it just doesn't work.

Sometimes, a circuit won't work because, well, one of the components has got to be used in a particular way.

Just like cells, all components have two contact points or connectors.

These points are where the component is connected to the rest of the circuit.

I can see there, there's a negative connector on one side with the black wire, and the red wire that's got the positive connector.

For a component of work, electricity has to flow through it, not just up to it, oh.

That means that one wire in the circuit has to be attached to one contact point to the component and another wire to the other contact point.

When a bulb is loose, it's not very easy to see the two connectors because they're very close together.

You can see there the screw pattern on the bottom part of the bulb.

That is one part of the contact.

The other side is the bottom of the bulb.

That's why we need a special holder to hold the bulb in place.

A little bit like this one I'm holding on my camera there.

The metal inside the bulb holder is able to connect everything together so you can attach some wires.

When a bulb is in a bulb holder rather than loose, the connectors are easy to see, and then you can connect the wires to.

You can see there the two screws that are the connectors for the bulb.

With buzzers, the two connectors are wires that come out either side.

Now, they're often covered in plastic, so you need to look for the metal wires at the very end.

Oh yes, I've got a buzzer here and I can see on mine that here's the red wire and there's only a tiny little metal strand there poking out, and on the black wire, well, there's no wire at all there, is there? Remember, the wire is the part that's inside the plastic covering.

Crocodile clips are really useful here because they can be clipped onto the uncovered metal and the buzzer's connector wires, and that will make the buzzer work in a circuit.

Now, you might have crocodile clips that are covered up like this just to protect your fingers if you're using really high voltage.

Sometimes though, they may have the rubber sleeving taken off completely, and so you can see the whole crocodile clip.

With motors, the two connectors are on the back.

Hmm, let me get my motor.

Yes, it looks similar to that one, and I can see there's a little connector just there and there's another one just there.

You can see them on that picture there sticking out at either end, there and there.

Now, it's quite easy to attach crocodile clips to these to connect the motor to a simple circuit, but I've noticed that sometimes they can be a little bit delicate, so you do need to be careful that you don't break them.

Here is a crocodile clip that we can use to click on, but if the wire or crocodile clip is too big, it'll be quite difficult to do that, won't it? Now ,to make bulbs or motors work, you've got to connect one wire from the circuit to each connector, so not both to the same one.

It doesn't matter which way round you do this, positive to positive, for example, or negative to negative there.

You could swap it round.

It could be positive to the negative or negative to the positive.

It's up to you.

In this case, it doesn't matter for the bulb.

Here, we've got a motor that's doing the same thing.

Both sides are positive and both sides are negative.

You could swap them over as well if you wanted to.

It doesn't matter, as long as the electricity is able to flow.

Either way, the bulb will light up and the motor will turn.

Buzzers are a little different though.

They will only work if the positive connector wire is connected closest to the cell's positive end and the negative connector wire is connected closest to the cell's negative end.

Here, you can see they're correctly connected.

You always know where the positive part of the cell is because it's the bumpy bit at the top.

Here's the positive that's going to positive and the negative that's going to the negative.

If it was incorrectly connected, positive to negative, for example, it wouldn't work.

Andeep and Sam now realise why their circuit didn't work.

"We joined everything together in our circuit," says Andeep, "But we connected the buzzer the wrong way round." Hmm, I wonder as well if they've checked to see if their crocodile clips are connected to those wires.

So let's stop and think.

Which of these components will only work if its positive connector is connected closest to the battery's positive end and it's negative connector is connected closest to the cell's negative end? Pause the video, and restart when you've discussed.

The answer here is a buzzer.

That's the only component that you'll need to work with that you'll need to make sure it's the correct way round.

Sometimes, circuits don't work because of one of the components is broken.

Andeep and Sam have built this circuit correctly, but the bulb won't light up.

Oh, how annoying.

How could they test which component is broken? Have a discussion, pause the video, and restart when you're ready.

Andeep says, "We should replace all the components "just in case they're broken." Sam says, "We should replace one component at a time "to find out which is broken." Which would you do here, and have a think as to why? Pause the video again, and restart when you discussed.

Okay, well Sam was correct here because we should replace each component at a time because if we throw away the whole lot, we could be throwing away components that are working.

When a circuit doesn't work, it is a good idea to test one component at a time rather than just replacing all of them.

You can use a circuit which you know works to test the components from your failed circuit.

You'd start with a complete working circuit, one that you know works, and then you would test the circuit that isn't working, each component at a time.

You could replace the working bulb with your test bulb like that.

If that works, you could then replace the working cell with your test cell like that.

If that works, you could replace each wire one at a time, testing wire one and testing wire two.

It's a little bit like changing just one variable in an investigation to make sure you've got the answer correct.

So let's stop and think here.

To solve problems with electrical circuits, what should scientists check? Pause the video, discuss those statements, and restart when you're ready.

Okay, the answer here, well, there's two answers.

It could be A or B.

Whether components are connected correctly is definitely something to check, and whether the components will work, you need to check that too.

Although it looks nice, it doesn't really matter what colours things are.

True or false here.

If a bulb is an electrical circuit and it doesn't light up, the cause will always be that the bulb is broken.

Is that true or false? The answer is false.

Can we justify this? Have a discussion, and think which of these statements is correct.

It could be because the bulb is broken, or it could just be because the circuit is not complete.

Okay, here's your next task.

You need to work like a scientist here.

You need to follow these steps to make sure that you fix a selection of circuits to make sure that they work.

Number one, trace that circuit, make sure it's a complete loop.

Number two, check each component is connected and make sure it's in the correct direction.

Number three, check whether any components are broken.

Of course, you need to make sure they're working.

For each circuit that you test, you need to make a note here, how you found the fault, how you corrected it, anything else that you notice.

Here are the circuits that you need to test.

You can't always identify the problem just by looking at it though, you need to dive in and test each one.

So pause the video here, and best of luck.

So how did you get on? Here are some notes that you could have made.

With one circuit, we noticed there was no wire joining the motor back at the other end of the cell.

We added a wire and then the motor worked.

We noticed that we could make the motor spin the other way by connecting it the other way round.

Ah, I see.

So if you connect two wires the other way round on a motor, it works but the wrong way.

You may also have found something like this.

With one circuit, we couldn't see anything wrong at first at all.

We made another circuit, which all worked, and then we tested all the bits from the broken one by replacing it one by one in the working circuit.

It turned out that the second purple wire was broken.

We found that the colour of the plastic coating on the wires in our circuits didn't really make a difference as the wire which worked in the end was also purple.

Of course, colour doesn't really mean much.

So here are some of the things that could have been wrong with the different circuits.

Number one, it was incomplete.

Number two, the buzzer was the wrong way round.

Number three, there was a broken bulb.

Number four, there was a broken wire.

Number five, there was a flat battery.

And number six, there was a broken motor.

I wonder if you found the same things too.

Well done.

Let's jump into the final part of our lesson.

Keeping safe with electricity.

Now, electricity and circuits are just about everywhere, and they're a part of our daily lives.

There are electrical circuits all around our houses, in our fridges, our microwaves, our television and our mobile phones.

Your home contains many different types of circuits, just like these homes here.

Electricians are experts in electrical circuits and help keep us safe when we use electricity.

You can see here an electrician working safely outside.

Oh, that looks very dangerous up there.

It looks like they're keeping safe though, they're tied onto that post and they're also wearing some protective clothing.

They check out if circuits have been built incorrectly and make sure that there's proper wiring.

Faulty or incomplete circuits can be dangerous, no matter if they're working or not.

The electricity could cause electric shocks or sparks.

We should not investigate electrical circuits at home.

We should always ask a professional like in the picture here to come and help out.

They know which parts are safe to touch.

They are fully trained to test circuits carefully, and they wear safety clothing and use special tools to investigate electrical systems safely.

When we use electricity and electrical appliances safely, we must follow some rules to stay safe.

You've always got to ask an adult for help, especially if you've not used them before.

Wires should be kept tidy and organised so that you can't trip over them.

Well, that's very important.

To avoid the risk of an electric shock, you never put liquids near electrical appliances.

You always dry wet hands before using electrical appliances.

You don't leave drinks near electrical appliances either, and you don't use electrical appliances in the bathroom or near sinks.

That looks very dangerous indeed.

Water and electricity do not mix very well.

You also must be careful with plug sockets.

You've got to make sure that you turn them off when you are not using them, and never stick anything inside them either.

They have special gates there that if jammed can cause a plug socket to malfunction, and it will give you an electrical shock.

So let's stop and think.

Which of these jobs would an electrician do? Read the statements, and restart the video when you're ready.

The answer here is B.

They'll check if circuits have been built incorrectly and they'll check for improper wiring as well.

Stop and think again.

Which of these rules should we follow when using electricity and electrical appliances? Read the statements, and restart when you're ready.

There are two answers here.

B, to keep electrical cables tidy, and C, don't put drinks near electrical appliances.

They could damage the appliance and then it won't work anymore.

Here is the final task.

Laura, Sam and Andeep are discussing electricity.

Laura says, "Electricity is dangerous, "so we shouldn't use it." Sam says, "Electricity is not dangerous "because we use electrical appliances every day." Andeep says, "Electricity can be dangerous, "but if we follow rules, we can use it safely." Wonder who you agree with here and why.

Can you give some examples to support your opinion? Pause the video, and restart when you've had your discussion.

Okay, in this case, Andeep is correct.

Electricity can be dangerous, but if we follow rules, we can use it safely.

For example, we should keep electrical cables tidy, turn plug sockets off when we're not using them, and never stick anything into plug sockets, and never mix liquids with electricity at all.

So let's summarise our lesson.

Now, there are many possible reasons why a particular circuit won't work.

To solve problems with electrical circuits, scientists test whether they're connected correctly and whether the components work.

When we use electricity and electrical appliances, we need to follow rules to stay safe.

Electricians are the experts here.

They're the experts in electrical circuits and help keep us safe when we use electricity.

Well, we've certainly gone through a lot in our lesson today.

I hope that when you are using electrical appliances that you know now how to be safe.

There's no need to be scared of electricity, but you do need to be cautious when you are around it because it could be very dangerous and can be harmful.

But as long as you are following those rules to keep safe, I know that you'll be very responsible scientists when you're investigating your circuits.

I've been Mr. Wilshire, thank you very much for listening.