Lesson video

Hi.

I'm Mrs. Hudson.

And today, I'm going to be teaching you a lesson called Fixing Faulty Circuits.

This is a key stationary science lesson, and it comes under the unit titled Series Circuits.

So let's get going.

The outcome of today's lesson is, I can describe how to build a simple test circuit, use it to check for faulty components, and find faults in a conducting circuit loop.

There will be lots of words that are used frequently in today's lesson, and those are the key words of the lesson.

Today, they are filament, faulty component, series circuit, complete circuit, and test circuit.

Let's have a look at what those words mean.

So the thin metal wire inside some light bulbs is called a filament.

When it gets hot, it glows and emits light.

A faulty component is one that is damaged or isn't conducting electricity properly.

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

A complete circuit is one where there are no gaps, so electricity is able to flow round the circuit.

And a test circuit is used to check if a component or another circuit is allowing electricity to flow through.

So if you want to pause the video to make a note of those keywords, then please do, but we're going to have a look next at the parts of today's lesson.

So the first part of today's lesson is going to be looking at circuit problems. Then we're going to move on to building and using a test circuit.

And then in the final part of today's lesson, we'll be looking at testing circuits as you build them.

But let's get going first with circuit problems. In a series circuit, if one component does not work, the circuit is broken, and it is not a complete circuit.

So we can see here, there's an image of a series circuit.

And if one of those light bulbs were broken, that would mean that the circuit would be broken.

So if this bulb breaks, it means that no electricity can flow through that component and therefore, the other light bulb would also not work.

This picture here is showing you a filament light bulb.

And a filament light bulb contains a thin wire that glows, and you can see where that purple line is pointing towards.

There is a thin wire that's glowing within that, and that is called the filament.

The filament is connected to the base to make a continuous loop.

And it is made of a metal and is a very good conductor of electricity.

Now the connections are made on the light bulb to the rest of the circuit on the bottom and the side, and they are made of metal, which allows electricity to flow through the light bulb to complete the circuit.

So as you can see here, through the connections, electricity and current can flow through the filament.

When electricity flows through the complete loop, the filament glows and the bulb lights up, which we can see on this diagram here, and that is why we can see when a light bulb is on because it's emitting light.

If too much electricity flows though, the filament will overheat and melt, which we can see in this picture here.

The loop is now broken and electricity cannot flow anymore because this is now an incomplete circuit.

So we can see that there's a gap where the filament used to be because the filament is broken so no electricity can flow through the filament.

We sometimes say the bulb has blown, but actually it's the filament that has broken.

It is now a faulty component.

Let's check our understanding of that.

We can see here that there's a circuit that's been set up that contains two cells and two bulbs.

In this circuit, one bulb blows.

What will happen to the other? A, it will stay lit, B, it will get brighter, or C, it'll go out? This is C, it will go out.

If one bulb in a circuit blows, the filament has blown.

And the filament no longer is complete, then the circuit isn't complete, and that means electricity cannot flow.

So the other bulb will also go out.

Really great job if you remembered that.

There are other reasons a circuit may not seem to work.

It could be that the bulb is rated too high and needs more electricity to glow.

It will still let electricity flow through, but it won't light up.

It could be that the bulb may not be screwed into the holder tightly enough and does not make contact with the connectors.

And if the bulb isn't making contact with the connectors, then that will lead to an incomplete circuit where electricity can no longer flow.

This bulb has not been screwed in enough, so you can see that the connectors on the side and the bottom, the bottom bit is not touching the metal plate at the bottom.

There's a gap which breaks the circuit, and this would mean that electricity cannot flow and it would be an incomplete circuit.

The metal wire inside a lead can break or it can get disconnected.

And we can see in this image here there's a metal wire, but if you notice that the end of the wire is disconnected from the connecting part.

Even a lead that looks fine can still be damaged on the inside.

So this image here is showing you two wires that look like they're absolutely fine, but potentially there could be an issue inside that you can't see.

That would mean that that wire didn't work properly and was faulty.

So it could be that there's a gap between the wire and the pin, but that it's enclosed in part of the plastic casing and you wouldn't be able to see that from the outside.

But that would lead to an incomplete circuit and electricity would no longer be able to flow.

Soldered joints can break or loosen.

So we can see here that there's some resistors and they are connected to a circuit board.

And there's a label there that says solder, and that's where the resistor has been soldered onto the metal casing so that electricity can flow.

And if those joints break or if they loosen, it leads again to an incomplete circuit where electricity cannot flow.

This resistor has a good connection making a complete circuit.

And we can see that the resistor is connected to the circuit board and it's a complete circuit, so electricity will be able to flow through.

There's no gap.

Here, the solder has become loose and the circuit is broken.

So the wire is still coming outta the resistor, but the solder joint has become loose and therefore there's a gap between the wire and the metal solder joint, which would mean that there's a break in the circuit and the circuit is now incomplete, which would mean electricity can no longer flow.

Let's check our understanding again.

Which of these problems does not cause a gap in a circuit? A, the filament melts, B, a bulb is rated too high and doesn't light, C, solder works loose, or D, the wire inside a lead breaks.

So if you got here B, a bulb is rated too high and doesn't light, then well done because that is the only option that does not cause a gap in the circuit.

If the filament melts, then that causes a gap.

If the solar works become loose, that also creates a gap, and a wire inside a lead breaking will also create a gap.

Great job so far.

We're ready now to do the first task of today's lesson.

Sophia has set up this circuit to turn on a motor and two lamps, it doesn't work.

List some checks she could carry out to fix the problem.

So if we look at that circuit there, we've got three cells, a motor, two lamps, and a switch.

So you need to say what she could check to potentially fix the problem.

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

Pause the video, and then press play when you're ready for me to feed back on the answers.

Let's see how we did.

So here are some of the things that Sophia could have done.

First of all, she could check that all the cells in the battery are the correct way round.

She could check each connection to see if it's loose.

She could replace each bulb one at a time with one she knows works.

She could replace the motor with one she knows works, replace each lead one at a time with one she knows works, try running the switch on and off, replacing it if necessary.

Test each component by connecting a bulb on either side of it to see if it works.

And finally, take the circuit apart and rebuild it, starting with a working cell and bulb then adding one component at a time.

Well done if you manage to get some of those in your answer.

What I would say is if you manage to get four or more, then that's absolutely fantastic.

And if not, maybe pause the video now and add anything into your answer to help make it a little bit better.

Great job so far.

So we know about circuit problems, let's move on now to building and using a test circuit.

Electricians can test components with a multimeter to see if they work correctly.

And what you can see in that image there is a multimeter, which is labeled, and then there are two wires attached to the multimeter, which the electrician is holding and pressing onto a component.

And what they are doing is using the multimeter and the current to check whether that component is working.

Usually this is to see if they allow electricity to flow through.

You can build a simple test circuit with a cell, a lamp, and some leads, which we can see in the diagram there.

You've got a cell, and then three leads, and a lamp.

You would check the circuit works by firmly touching the leads together, which are circled.

So you would have to pick the leads up and firmly touch 'em together to see if the light bulb lit up.

If the light bulb did light up, then this would show that the circuit was working.

So the lamp should light up.

If the lamp doesn't light up, then replace the components one by one until it does.

The test circuit is being used to test a lead.

The lamp has not lit up.

This could be because the leads are not pressing firmly enough.

So we can see here that there is a hand which is using one of the leads to press down on another lead, but then the other two leads are just resting on each other.

It might be that they need to be pressed down more firmly to make a better connection, or it could be that the lead being tested is faulty.

You can practice using a test circuit to see if different components and objects allow electricity to flow through.

So objects can also be tested to see if they are conductors or insulators.

What you would do is place the components or the object in the gap within that circuit and then press firmly down with the two exposed wires to see if that object completed the circuit.

So if the bulb lit up, then that object would be a good conductor because it's obviously allowing electricity to flow through it.

If an object was placed down, the leads were pressed down firmly and the bulb didn't light up, then this would suggest the object was an insulator because electricity was not flowing through.

Let's check our understanding so far.

Which two of the following would stop a lamp in a test circuit from lighting? A, the test bulb is screwed in too tight, B, the leads are not pressed firmly enough, C, the test bulb filament has melted, or D, the cell is the wrong way round.

So hopefully for this, you got B and C.

The reason why A is wrong is because the test bulb being screwed in too tight would lead to an incomplete circuit.

And then D, if the cell is the wrong way round, this just means that the current flows in the opposite direction, but it wouldn't cause the circuit to be incomplete.

Well done if you got that right.

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

And you need to build and use a test circuit to check different components and objects to see if they conduct electricity.

And you're going to put your results into the table and the table is shown on this slide.

So there's various different objects that you're going to test and you can use some of your own objects as well if you want to.

So on here we've got a lamp, a lab lead, resistor, plastic ruler, steel scissors, and pencil lead.

And then there's two other columns.

One is conductor column, the other one's an insulator column.

And you to either say yes or no there to say whether that object is a conductor or an insulator, depending on what happens in your test circuit.

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

If you have a go at that, fill in your table and then come back ready for me to give you the answers.

Let's see how we did.

So what you should have found is that the lamp was a good conductor.

The lab lead was also a good conductor, and the resistor was a good conductor, so they all let electricity flow through.

You should have found that the plastic really was an insulator, and the light bulb did not light up because the plastic ruler does not let electricity flow through.

The steel scissors are also good conductors.

And pencil lead is also a good conductor.

It's not actually lead, the metal.

Pencil lead is made from a substance called graphite, which is a conductor of electricity.

So you should have found that the light bulb did light up when you had pencil lead.

Really great job if you managed to get those right.

Well done.

We can now move on to the final part of today's lesson, which is testing circuits as you build them.

So let's get going.

If a circuit contains a lamp, it can be used to check whether the circuit is working as it is built.

So here we can see we've got a circuit set up with two cells that make a battery, a motor, two lamps and a switch, which is shown as being closed.

You don't need a separate test circuit here.

Start by building this circuit with one lamp and one cell.

So you would start the circuit with one cell and one lamp, you do not need a separate test circuit.

So if the lamp lights, you know that the components are working correctly.

So if you set up your one cell with one lamp and the lamp lights, you know that those two components are working correctly.

And then you add another component such as the motor and check that the lamp works.

And if the lamp lights up, you know that the motor is also working.

Add the next lamp and check if they both light up, so you then add in another lamp.

And if that lamp also lights up, you know because the rest of the circuit is functional that that lamp also must be functional.

And then we're going to add the switch and then make sure that the switch is closed so that the circuit is complete and electricity will flow through, and the circuit should light up.

If the lamps light up and the switch is closed, you know that the switch must be working.

But if the lamps don't light up, then you would note that it was a switch that was faulty.

And then after you've added the switch, you're going to add in the second cell and again see if the lamps light up.

Again, if the lamps didn't light up at this point, you would know that it was that cell that you've added that is faulty.

If any component causes a lamp to go out, you know that it is faulty and should be replaced.

The important part of this process is that you start with the the cell and one component, which is the lamp, and then one by one add in other components until the lamps don't light up.

Let's check our understanding again with a true or false question.

If a circuit has a fault, a test circuit is needed to check it.

True or false.

This is false.

Let's justify that answer now.

A, the circuit can be built component by component, checking that it works each time, or B, it is not possible to tell which component is faulty without a test circuit.

Hopefully here you've gone for A, the circuit can be built component by component, checking that it works each time.

So we just use the example of using a cell and a lamp to begin with and checking that the lamp lit up, and then one by one adding in each component, and then finding the component where the lamp doesn't light up and knowing that that is the faulty component.

Really great job if you got those right.

Well done.

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

Laura and Jacob have been building circuits and have found some faulty components.

Laura says, "Faulty components made learning more difficult," and Jacob said, "Faulty components helped me learn better." Explain why both pupils might think that they are correct.

Then, suggest whether or not it is beneficial to have faulty components in laboratory equipment.

So you need to think about this from both points of views.

Why is Laura partly correct and why is Jacob also partly correct? I'm sure you're gonna do a fab job.

Have a go.

Then come back to me when you're ready for me to go through the answers.

Let's see how we did.

Now, faulty components can be a problem because they may prevent pupils from successfully carrying out experiments, causing them to miss out on learning.

So if you are in the classroom trying to build a circuit and there's faulty components, that can be frustrating if they're not working and could hinder your learning.

On the other hand, they can provide an opportunity for pupils to practice their skills and take responsibility for their own learning.

Pupils who feel confident may see faulty components as a chance to learn, while those who are less confident may need more support.

Fantastic job if you've got some of those ideas down.

If you need to pause a video now to add anything into your answer, then please do.

But we're going to summarize everything we've learned in today's lesson.

So today's lesson has been about fixing faulty circuits.

And we started by saying faulty components create a gap in a complete circuit, preventing it from working.

And an example of that was a light bulb which contains a filament that glows, and that filament's made of metal.

But this can melt and break the circuit.

We then said that a test circuit can help identify faulty components.

And if a circuit does not work, each component can be tested separately using a test circuit to check whether it is functioning.

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

And I look forward to seeing you next time.