Hello, my name's Dr.

Dello and I'll be leading you through today's lesson.

Today's lesson is about the loops of a parallel circuit and it comes from the resistance and parallel circuits unit.

The outcome for today's lesson is I can divide a parallel circuit into a set of nested series circuits.

Let's begin.

These are today's keywords.

The first set are series circuit, and this is an electric circuit with one complete loop from one end of the battery round to the other end.

The second keyword is battery, and this is a component that uses a chemical reaction to make electric charge flow round a circuit.

A battery is a set of cells connected together, so you may also see the word cell used.

Our next set of keywords are parallel circuits, and this is a circuit with more than one complete loop from one end of the battery round to the other end.

Finally, we have potential difference and this is a more scientific term for voltage.

In this lesson about loops of a parallel circuit, there are two parts.

First of all, we'll talk about the parallel circuit loops and then we'll move on to batteries in parallel circuits.

Let's start with parallel circuit loops.

The circuit shown is a series circuit.

There is a single loop connecting the battery and the lamp.

A second series loop can connect another lamp to the same battery, using a different set of wires.

This forms a separate loop.

A third series loop can connect a third lamp to the same battery using another set of wires, and you can see the separate loop over here.

These three wires can be replaced.

It can be replaced with a single wire and branches to connect the lamps together.

These three wires can also be replaced.

Another single wire and branches connect the lamps together and to the battery.

The original circuit can be simplified with these connecting wires instead of each separate loop and they can be simplified further into a circuit diagram.

These three pictures are the same circuit.

Look at them carefully to recognise that this is the case.

Let's do a check for understanding.

Which of the following statements about the circuit shown are correct.

All of the lamps are identical, so the choices are A, the circuit is three loops that include the battery.

B, if one lamp blows, the others will go off.

C, the lamp closest to the battery will get the highest voltage.

D, each lamp is directly to both ends of the battery.

Pause the video now.

Study the circuit carefully and make your choices.

Come back when you want to check them.

Welcome back.

If you chose A, the circuit has three loops that include the battery, that's correct.

There are actually three loops that connect the battery.

If you chose D, each lamp is connected directly to both ends of the battery.

That's also correct.

If you follow the leads through, you'll see that each lamp has a direct connection to the battery.

Answer B, if one lamp blows, the others will go off is not right.

The lamps can work independently and answer C, The lamp closest to the battery will get the highest voltage, is also not correct because the wires make no difference.

Each of the lamps is connected by the wires directly to the battery.

Well done if got that right.

Each of the diagrams below show connections to a battery that are effectively the same.

If there are no components along the wires, the connections can be anywhere as long as they lead directly to the battery.

Let's check your understanding.

Which of the following circuits is the odd one out? Pause the video now.

Study the circuits carefully make a choice and come back to check how you've done.

Welcome back, if you chose circuit B, that's correct, that's the odd one out.

If you look carefully, there are two lamps in the middle branch, which are in series.

If you look at answers A and C, there are no lamps in series.

They're all in parallel.

Well done if you got that right.

Each loop in a parallel circuit is like a separate series circuit.

We can see the second lamp with its loop on the left and we can see the separate series circuit on the right.

Here's the lowest loop for the lowest lamp and also the outermost series circuit.

Each one of these lamps has its own separate series circuit directly it to the cell or battery.

Let's try a check for understanding.

Is this statement true or false? The two circuits shown are the same.

Pause the video now study the circuits carefully and make your choice.

Then come back to check how you've done.

Welcome back.

If you chose true, that's correct.

Now's the time to justify your answer.

The choices are A, each lamp is connected on its own loop with a battery or B, the wires are in different positions, so they are different circuits.

Pause the video now.

Make your choice for your justification and then come back to check how you've done.

Welcome back.

If you chose answer A, that's correct.

Each lamp is connected on its own loop with a battery.

For answer B, the wires are in different positions, so they're different circuits.

Well, the wires are in different positions, but that doesn't matter, circuits are identical.

Well done if you got that right.

Here is our circuit with three lamps connected in parallel.

This middle lamp can be moved without changing connections to the battery.

It can be lifted up and placed above the battery on the other side.

The new loop position does not change the way the circuit works.

The lamp has just been lifted up and moved to the other side of the battery.

This circuit is the same as this circuit.

They'll work in exactly the same way.

The circuit pictures can be shown as circuit diagrams. On the left, we've got the three lamps lined up underneath the cell and on the right we have one lamp above the cell and two lamps below.

These two circuit diagrams are exactly the same.

This is the first loop connecting the first lamp.

This is the second loop and it connects the second lamp.

The position and size of the loop is not important.

Finally, this is the third loop that connects the last lamp.

All the lamps are connected directly to the cell so they all behave in exactly the same way.

Let's do a check for understanding.

Which of the following statements about the current in the loops of the circuit shown is correct.

The choices are A, the current in all loops is pushed with the same voltage.

B, the current is pushed most in the loop closest to the battery.

C, the current is pushed most in the loop farthest from the battery.

Pause the video now.

Study the circuit very carefully.

Make your choice and then come back to see how you've done.

Welcome back.

If you chose answer A, the current in all loops is pushed with the same voltage, that's correct, well done.

Answer B, the current is pushed most of the loop closest to the battery is not right.

The position of the loops doesn't matter and answer C, the current is pushed most in the loop farthest from the battery is also not right.

The loop position does not matter.

In parallel circuits, the positions of the wires and the components are not so important.

It is how the loops or branches are connected to the battery that matters.

A good way to analyse the circuit is to follow each side of a loop back to the sides of the battery.

For the first bulb, you can see in red that the wires are connected directly to the battery on the left and in blue the wires are connected directly to the battery on the right.

Likewise, for the second bulb, there's a direct connection on the left in red to the battery, and then there's a direct connection on the right to the battery.

And finally for the last bulb, it has a direct connection on the left to the battery and a direct connection to the battery on the right.

If there are no other components in the way, the component will get the full battery voltage.

Here's a true false check for understanding.

Is this true or false? The two circuits shown are the same.

Pause the video now look at the circuits and then make your choice of either true or false.

Welcome back, if you chose true, that's correct.

Now's the time to justify your answer.

The choices are A, the loops are in different positions or B, each lamp connects directly to the battery.

Pause the video now, make your choice, then come back to see how you've done.

Welcome back.

If you chose B, each lamp connects directly to the battery, that's correct.

If you trace the wires from each bulb round to the battery, you'll see that they connect directly in both circuits.

Answer A, the loops are in different positions is technically right, but it has no effect.

Well done if you got that right.

We've come to the end of this section.

Here's a practise task to see how you're doing.

You're going to build circuits A and B and check that they work.

You'll then write down what happens to the lamp and the motor.

When you've done that, predict what will happen to the lamp and the motor if you build circuit C using the same battery and then explain why you think this.

Part three, build circuit C.

Part four, describe what happens to the lamp and what happens to the motor.

And then part five, were your prediction and explanation into correct.

If not, explain why and or improve them.

Pause the video now.

Go ahead and carry out this task and then come back to see how you've done.

Welcome back.

Here's some sample results and explanations.

See how yours compare with them.

For number one, when you've built these two circuits A and B, the lamp lights brightly and the motor spins fast.

For number two, the prediction is the lamp will light but won't be as bright as before and the motor will spin but more slowly than before.

For number four, when the circuits have been built and tested, the lamp lights as brightly as it did in circuit A and the motor spins as fast as it did in circuit B, so the prediction wasn't correct.

So for question five you should have said, "My predictions for circuit circuity were not correct.

The lamp did not get dimmer and the motor did not get slower.

They stayed the same as they were before.

I should have remembered that the lamp and motor are each connected directly to the battery in separate loops, so they will get the full voltage.

This means they will work as well as if they were in single separate circuits like in A and B." That was quite a tricky task if you managed to get that right, really well done.

We've now reached the second section, batteries in parallel circuits.

When batteries are connected together in series, their voltages add together.

Here we are adding two more batteries to the first battery and they're all 1.

5 volt batteries, so if you add up 1.

5 volts plus 1.

5 volts plus 1.

5 volts, the total is 4.

5 volts.

These three batteries and series will each add up together to give 4.

5 volts.

Potential difference is another name for voltage.

The potential difference is a bit like that gravitational energy in the potential store, which is due to height.

We can use the analogy or model of height to explain what has meant by potential difference.

Here's a ball at the foot of a cliff, lifting the ball up the cliff transfers energy to the ball.

Energy is transferred to the gravitational storm, lifting a ball twice as high, transfers twice the amount of energy to it, so we have energy in the gravitational store just like the potential difference due to a battery.

Increasing the height increases the energy in the gravitational store.

Adding a battery in series increases the potential difference.

The two 1.

5 volt batteries connected are shown in series.

They give a combined potential difference or voltage of 3.

0 volts.

1.

5 volts plus 1.

5 volts equals 3.

0 volts.

Adding a battery in parallel does not raise the height of the potential difference.

The two batteries shown when connected in parallel can only give a maximum potential difference or voltage of 1.

5 volts.

To get more than 1.

5 volts you'd need to stack them in series.

In parallel, you only get 1.

5 volts.

Even adding a third battery in parallel only gives a potential difference or voltage of 1.

5 volts.

However, three batteries contain more chemicals than one, so the batteries will work for longer.

The simulation below shows that the voltage is the same across the three batteries.

The voltage across the batteries when they're connected in parallel stays the same.

Let's try a check for understanding what will the reading on the volt metre in the bottom circuit be? Will it be A, 3.

0 volts, B, 1.

5 volts, C, 0.

75 volts or D 0.

0 volts? Pause the video now.

Make your choice, come back and see how you've done it.

Welcome back.

If you chose answer B, that's correct.

The volt metre will read 1.

5 volts.

Adding another 1.

5 volt cell, an identical cell won't raise the voltage.

Identical cells in parallel will give the same voltage.

Well done If you got that right.

This lamp, which is connected to three batteries in parallel will light brightly.

This lamp will be just as bright even though there's only two cells because the voltage will be the same and this lamp with just one cell will be just as bright as the other two lamps.

The voltage across a battery or batteries in parallel stays the same.

Here's a quick check for understanding.

Which of the following lamps will stay lit for longest? Will it be A, B or C? Pause the video now make a choice and then come back to see how you've done.

Welcome back.

If you chose answer A, that's correct.

There are three batteries connected to this lamp, so there's three times as much of energy in the chemical store off the batteries, lamp A will last the longest.

Well done if you got that right.

We've come to the end of this section and here's a task to practise what you've learned.

Sam and Andeep are building some circuits and making predictions.

The circuits are number one, two, and three.

Sam says, "The lamps will be brightest in circuit three and dimmest in circuit one." Andeep says, "The lamps will be the same brightness in all of the circuits." Identify whether each pupil is correct or incorrect and explain why.

Pause the video now.

Go ahead, study the circuits and then write out your explanations and come back to see how you've done.

Welcome back, Andeep is correct and Sam is incorrect.

The lamps will all have the same brightness because the voltage across each battery is the same.

This means that the voltage across each branch of the circuits is also the same.

If the voltage across each branch and each lamp is the same, then all of the lamps will have the same brightness.

Well done if you've got that right.

We've come to the end of this lesson.

Let's summarise what you've learned.

A parallel circuit is made of loops that branch off at junctions.

Each loop goes from one end of the battery round to the other end of the battery, like a separate series circuit.

The voltages across each loop of components is the same as the voltage across the battery.

Batteries in parallel will give the same voltage as a single battery but will last longer as there are more chemicals in them to react.

You've done really well to complete this lesson.

I hope to see you again soon.