Hello, I'm Dr.

De Mello, and today I'll be teaching you today's lesson on electricity.

Today's lesson is about faulty circuits from the unit on Series circuits.

You're going to be able to describe how a simple test circuit can be built, and then you're going to be able to use it to test for faulty components, which are often a problem in circuits.

You'll be able to find faults in a conducting circuit loop and fix them.

So let's start.

Here are today's key words.

The first is filament.

This is the fine metal wire inside an incandescent light bulb.

It heats up, glows, and gives out light when electricity flows through it.

Next keywords are faulty component.

Often when you work in circuits, components don't work.

They're faulty for various reasons.

In today's lesson, we'll be looking at how we find them and what to do about them.

Series circuit are the next pair of keywords and they are about a circuit that's a complete circuit that allows electricity to flow, and I've mentioned complete circuit while talking about series circuits.

It's a complete loop where electricity continuously flows.

Finally, we have test circuit.

You are going to learn to build a test circuit, which is actually easier than it sounds, and use it to test for faulty components.

These are the keywords defined.

If you need to have a look at them, pause the video.

You can read through at your own speed and do look out for them in the video that's following.

In the lesson, in fixing faulty circuits, we're going to look at, first of all, circuit problems. We'll then go on to building and using a test circuit.

And then finally, you'll be testing circuits as you build them.

So starting with circuit problems. Here is a series circuit.

It's got a battery and two bulbs all connected in one loop, a series circuit.

If one of these components doesn't work, the circuit is broken, and this isn't a complete circuit.

It doesn't work.

So if this bulb breaks, no electricity can flow and none of the components will work.

The other bulb goes out.

And you can see, this purple loop is broken.

So there's a gap.

Electricity can't flow.

A filament bulb contains a fine wire that glows.

Here you can see the filament glowing.

It's giving off light because electricity is flowing through it and making it hot.

The filament is connected to a base and it needs to make a continuous loop so that you have a complete circuit.

It's made of a metal, which is a conductor of electricity, and the connections on the bulb fit at the bottom and the side.

These allow current to flow through to complete a series circuit.

When electricity flows through the loop, the complete loop, the filament lights up and gives us the light that we use.

If too much electricity flows, the filament heats up too much and it can melt.

At this point, the loop is broken and the electricity can't flow.

We say that the bulb is blown because of this gap.

This bulb is now a faulty component and it'll stop the circuit working.

It doesn't work and nothing else in a series circuit that's connected with it will work either.

Let's check your understanding.

So in this circuit we've got two batteries and two bulbs connected in a series loop.

If one bulb blows, what will happen to the other one? Will it A, stale it, B, get brighter, or C, will it go out? Pause the video, make your choice, and then come back and check your answer.

Welcome back.

If you chose, it will go out, well done.

You got it right.

The circuit is broken so no electricity can flow, so none of the bulbs will light.

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

If the bulb is rated too high and needs more electricity to glow, it will let electricity flow but it won't light up.

This is a special case.

The circuit is still working, it's still complete, but the bulb doesn't actually do its job because not enough electricity is flowing through it.

The bulb may not be screwed into the holder tightly enough.

You can see here, there's a bulb, and below it, there's a holder into which it gets screwed in.

If it's not screwed in tightly enough, it doesn't make contact with the conductors, which means there's a gap in the circuit and it doesn't work.

So this bulb has not been screwed in tightly enough and it's not making contact with all the parts of the holder.

Magnifying the image, we see that there's a gap between the bottom contact and the bottom part of the bulb.

No electricity can flow.

This stops the circuit working.

So if you're working with bulbs in a circuit and they don't work, check that they're screwed in fully into the holder.

To connect our circuits, we use metal wires that are covered in plastic.

These are our connecting leads.

The metal wire inside the lead can get broken or it can get disconnected.

In this example, both the plastic and the metal wire are broken and disconnected from the pin.

A lead could look fine, but it may be damaged inside.

There may be a gap between the wire and the pin that gets connected to.

So in this case, this lead won't allow electricity through.

Soldered joints are used to connect up components such as resistors to other ones on a printed circuit board.

You can see the shiny shoulder over here and it's made a nice connection from the component to the circuit board so that electricity can flow through this continuous loop.

This resistor shows a good connection to make a complete circuit.

You can see the grey solder and there's no gap between the black resistor wire and the black part of the printed circuit board.

Over time, as the circuit board bends and the resistor moves around, the solder can become loose and break the circuit.

You can see a gap here between the solder, grey, and the black wire of the resistor.

Now the resistor has broken the circuit and electricity can't flow, which means other components won't be able to work either.

This is a fault in the circuit.

Let's test your understanding.

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

Pause the video, make your choices, come back and we'll check your answers.

Okay, welcome back.

If you chose a bulb is rated too high and doesn't light, that's correct.

Well done.

If the filament lamp has the filament melting, as in A, then that causes a gap.

If the shoulder works loose, again, that'll cause a gap.

And if the wire inside the lead cracks and pulls away, there'll be a gap through which electricity cannot flow.

We've come to the end of the section.

Let's try task A to practise your learning.

Sofia has set up the circuit to turn on a motor and two bulbs.

It doesn't work.

List some of the things she could do to make it work.

So the circuit has three batteries in it.

The batteries are connected in order to a motor, two bulbs, a switch, which is closed, and back ground.

It is a complete series circuit.

List as many of the things you can think of.

Aim for about five that she could do to make it work if it doesn't.

Pause the video now, write off your answers, and come back and we can check them.

Okay, welcome back.

These are the possible answers you could use.

If you've got any of them, well done, but do look at all of them because they're all valid.

So Sofia could do some or all of the following.

She could check all the batteries are the correct way around.

So she could check the holders to make sure that they're pointed in the right direction.

But then it's also important to look inside the holder and make sure that the batteries aligned the right way around.

She could check each of the connections to make sure that they're not loose.

Sometimes over time, the pins that plug into the sockets work loose.

Just check that there aren't any that are loose.

If they're loose, replace the components and see if those work.

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

She could replace the motor of one she knows works.

She could replace each of the leads with one she knows works, one at a time.

It's important to use something that works so that she knows that she's not replacing a faulty component with another faulty component.

She should try switching the switch on and off, replacing it as necessary.

She could then test each component separately to see if it works by connecting a bulb either side of it.

Finally, if none of that works, she could take the circuit apart and rebuild it, starting with a battery and a bulb and checking that works.

If that works, she could add a component, one at a time, checking that the bulb works as she goes.

If you manage to get any of those right, well done.

If you manage to get three or four, that's really great.

And if you've got more than that, excellent.

Let's start the next section, building and using a test circuit.

So electricians often test components with something called a multimeter to see if they work correctly.

So here, you can see the electrician pressing down with two leads on a component.

They're testing to see if the component is working correctly, and one of the things they can do to see if it's allowing electricity to flow.

You can build a simple test circuit with a battery, a lamp, and some leads.

You check that the circuit itself works by pressing the leads firmly together.

The battery should light up the lamp.

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

So once you've got a working test circuit where a bulb lights up when you complete it, you can test other components.

So this test circuit is being used to test a lead.

The lamp has not lit up.

There are reasons which could cause this.

You know the circuit itself works because you've tested it already.

The leads are not pressing firmly enough, so it's important to press both leads.

You can see one lead is being pressed on the right-hand side, but on the left-hand side it's just resting.

That could not be making a a good contact.

So both points should be pressed down firmly.

If doesn't work, the lead being tested is likely to be faulty.

You could test another lead.

And if that works, you know that the first lead you tested was faulty and shouldn't be used.

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

The objects can be tested to see if they're either conductors or insulators.

You place the component in the middle between the leads and then press the ends of the leads onto it to see if it conducts electricity.

Let's check your understanding.

Which two of these would stop a test circuit from lighting? The choices are A, the test bulb is screwed in too tight, B, the leads are not pressed firmly enough, C, the test bulb filament has melted, And finally, D, the battery is the wrong way around.

Pause the video now, make your choices, and come back to check your answers.

Welcome back.

So if you said the leads are not pressed firmly enough, that's correct.

It could stop a test circuit working.

If you said the test bulb filament has melted, again, that would stop the test circuit working.

A, the test bulb is screwed in too tight, shouldn't affect the test circuit.

It should just be difficult to undo, but the circuit would still be complete and it would still work.

If the battery was the wrong way around, it would still work.

The electricity would still be able to flow.

It would just flow in the opposite direction.

It would still be a complete loop.

So well done if you've got those right.

We've come to the end of this section, well done.

Let's practise what you've learned.

So you're going to build a test circuit.

as you've been shown, and you're going to check different components and objects to see if they conduct electricity.

You'll put your results in a table.

So in the table, on the left, we have different objects.

I've listed a few for you to to look at.

We've got either the object as a conductor or an insulator.

So you can write in yes into either the conductor column or the insulator column.

The objects listed are a lamp, a lab lead, a resistor, and so on.

Use a few electrical components that you have, but you're free to test a few other things.

When you've completed your tests, come back and we'll check your answers.

Pause the video now and see you later.

Welcome back.

So if I was using a lamp, it would be a conductor, unless it was faulty.

A lab lead should also be a conductor.

A resistor, again, is a component that should conduct electricity.

A plastic ruler doesn't conduct electricity.

It's an insulator.

Steel scissors, as long as you are testing the metal bits and not plastic coatings or painted coatings, are a conductor.

So they should be yes.

And then a tricky one, pencil lead should only just conduct.

The lead inside a pencil is actually not lead, the metal, but is made of graphite, and graphite allows some electricity through.

Hopefully you've tested quite a few other things and found out whether they're conductors and insulators.

Well done, we've reached the end of this section.

We've reached the last section.

This one is on testing circuits as you build them.

In this case, we're not going to use a separate test circuit to find faulty components.

We'll test the circuit as it's being put together component by component.

So if the circuit contains a lamp, then it can be used to check the circuit is working as it's being built.

We have the circuit that's got two batteries, then a motor, two bulbs or lamps, and then a switch is shown closed.

You don't need a separate test circuit for this circuit because you can start building this circuit with one lamp and one battery.

So picking out one battery in one lamp, you connect it together to check that it works.

If the lamp lights, you know both components are working correctly.

You could add another component, such as the motor.

And if the bulb still works, you know the circuit's still working, so you are good to go.

You could add the next lamp.

And if that lights up, both lamps need to light up, you know the circuit is still working.

You can then add the switch and check when that's closed, the circuit still works, followed by the second battery, ensuring that the circuit still works.

If at any point the new component stops the circuit working, you know that component is the problem.

Replace that component and then start again at that point.

So the rule is if any component causes the lab to go out, you know there is a fault, and the component should be replaced.

Let's check your understanding.

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

Is that true or false? Make a choice and then come back to check your answer.

Welcome back.

If you chose false, that's correct.

You don't need a test circuit all the time.

To justify your answer, pick either A or B.

A, the circuit can be built up 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.

Again, pause the video, make a choice, and come back to check your answer.

Welcome back.

If you chose A, the circuit can be built up component by component, checking that it works each time, that's correct.

You don't always need a test circuit so long as you can see what you've built at each stage is working.

Well done.

Let's move on to the final task.

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

Laura says, "Faulty components made learning more difficult." Jacob said, "Faulty components helped me learn better." Explain why both students thought they were correct and then suggest whether or not it is good to have faulty components in laboratory equipment.

Pause the video, write out your answers, and then come back and check them.

Aim for a few points for each person explaining why.

Welcome back.

You could have written the following, "Faulty components are a problem because they could prevent pupils carrying out experiments successfully and so miss out on the learning the tasks that they're supposed to do to improve their understanding.

On the other hand, faulty components can give pupils a chance to practise the skills they're learning and so take responsibility for their own learning.

Testing each component, one at a time, will improve your skills.

If students feel confident, then they can use faulty components as an opportunity to learn better.

If they're not confident, they'll need some help." Well done on finishing this lesson, we'll next look at the summary.

To summarise, faulty components can cause a gap in a complete circuit and can stop it working.

A bulb has a filament that glows.

This can melt and break a circuit.

A test circuit can be used to help find faulty components.

And finally, if a circuit does not work, each component should be tested separately with a test circuit to check it is working.

Well done on completing this lesson, and I hope to see you soon.