Hello, I'm Dr.

Dumello, and I'll be teaching you today's lesson.

Today's lesson is called comparing series and parallel circuits and it comes from the unit resistance and parallel circuits.

The outcome we're going to cover today is, I can compare the properties of series and parallel circuits that have the same components.

These are today's keywords.

We start with series circuit.

This is a circuit with a single loop.

Next up is current, and this is the rate of flow of charge in a circuit.

We then have voltage, which is a measure of the push an electric cell will give to chargers, and finally we finish with parallel circuit.

Now this is a circuit with junctions that lead to separate loops.

If you'd like to study these keywords a bit further, pause the video now, have a look at them and then look out for them in the video.

This lesson on comparing series and parallel circuits has three parts.

We'll start with current and voltage in a series circuit, we'll then go on to adding components to a branch and we'll finish with adding branches to a parallel circuit.

Let's begin on current and voltage in a series circuit.

This is a series circuit.

There is a single loop going round this series circuit and it's highlighted here in purple.

The current is the same everywhere along this loop, adding components anywhere in the circuit will increase the resistance and cause the current in the circuit to decrease.

Again, the decreased current is the same everywhere in the circuit because it is a single loop and the current goes round everything in the loop.

Let's do a quick check for understanding to see if you've understood the last point.

What does adding components to a series circuit do? The choices are A, it increases the current, B, it increases the voltage, or C, it increases the resistance.

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

Welcome back.

If you chose it increases the resistance, that's correct.

Adding components won't change the voltage because that depends on the cell and if you increase the resistance, the current will decrease, so A and B are incorrect.

Well done if you've got that right.

We'll now look at the effect of adding another cell to the battery, which cause the current to increase.

The cell will be added in series, and the increased current is the same everywhere along the loop.

Here is a quick check for understanding.

What current will a battery of two 1.

5 volt cells cause in a series circuit if a 1.

5 volt cell causes a current of 0.

2 amps? The choices are a, 0.

2 amps, B, 0.

4 amps, C, 1.

5 amps and D, 3.

0 amps.

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

Welcome back.

If you chose 0.

4 amps, that's correct.

one 1.

5 volt cell will give you 0.

2 amps, so two of them will give you double that so it'll be 0.

2 doubled, which is 0.

4 amps.

Well done if you got that right.

The cell in this circuit provides a voltage of 3.

0 volts to push current through the bulb.

The voltage across the bulb is 3.

0 volts.

It'll be the same as the voltage of the cell because it's the only component in the circuit.

The same 3.

0 volt cell can push current through two bulbs.

The resistance is now higher, but the cell can't push harder.

The bulbs will be dimmer as a result.

The voltage across each bulb is 1.

5 volts.

1.

5 plus 1.

5 equals 3.

0 volts.

The bulbs are sharing the voltage.

Using a battery of two cells will light the bulb more brightly.

So we have two cells here that are 3.

0 volts each.

The voltage across the bulb is now 6.

0 volts.

Here is a check for understanding.

What is the voltage across one of these identical bulbs in the circuit shown? There are two cells in the battery of 3.

0 volts each and there are three identical bulbs in a series circuit.

The choices are A, 1.

5 volts, B, 2.

0 volts, C, 3.

0 volts, or D, 6.

0 volts.

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

Welcome back.

If you chose 2.

0 volts, that's correct.

The total voltage would be 6.

0 volts and that's shared between three bulbs, so they each get one third of six volts, which is 2.

0 volts.

Well done if you got that right.

Now's the chance to practise what you've learned.

Your task is, to explain what will happen to the current, resistance and voltage in a series circuit in the following cases.

Number one, the number of components but not the electrical cells is increased.

And then number two, the number of electrical cells is increased.

Pause the video now, go ahead and write out your explanation and then come back to see how you've done.

Welcome back.

You could have written something like this, for number one, the resistance will increase and the current that can flow through them will decrease.

The voltage from the cells will remain the same.

For number two, the voltage from the cells will increase and the current that flows will also increase.

The resistance from the components will remain the same.

If you wrote something similar, well done.

We're now ready to move on to the next section.

Adding components to a branch.

Series circuits can be combined to make a parallel circuit.

This is one series circuit shown here.

This is another series circuit with one bulb in it and it's identical to the previous series circuit.

Those two series circuits can be combined to make a parallel circuit like this.

A parallel circuit behaves like separate series circuits joined together.

There is one series circuit here highlighted in green, and then there's another series circuit here also highlighted in green.

In this parallel circuit, the voltage across the electrical cell is the same as the voltage across each branch.

Both branches have 3.

0 volts across them.

The voltage of the cell that's above them.

since the voltage across each branch is the same, the current will also be the same.

Each branch will have 0.

2 amps flowing through.

This is because 0.

2 plus 0.

2 equals 0.

4 amps.

The current has split into two branches.

Let's check your understanding.

What is the current flowing through the lower bulb in the circuit shown? These two bulbs are identical.

You have a choice of a, 0.

1 amp, B, 0.

2 amps, C, 0.

3 amps and D, 0.

4 amps.

Look at the circuit carefully, pause the video, make a choice and then come back to see how you've done.

Welcome back.

If you chose 0.

3 amps, that's correct.

The current will be the same as the other bulb in the circuit which has 0.

3 amps shown flowing through it.

Well done if you've got that right.

The number and type of components in each branch does not affect the voltage as the branches are connected directly to the cell.

Adding a resistor to this middle branch won't change the voltage across the whole branch.

Even adding another bulb to that branch won't change the voltage across the whole branch.

In the lower, you can add two components as well and the voltage will still be 3.

0 volts.

The branches all will have 3.

0 volts across them.

The components in a single branch will share the voltage.

Increasing the number of components in a branch decreases the voltage across each component.

Let's examine the circuit to see how this works.

The branch with a single bulb gets 3.

0 volts, so the voltage across that bulb is 3.

0 volts.

In the lower branch, these bulbs each get 1.

5 volts, 1.

5 plus 1.

5 equals 3.

0.

The bulbs are sharing the voltage so they get less.

Since the bulbs are identical, they get the same voltage each.

The branch with two bulbs will have a higher resistance and so will have a lower current.

The single bulb gets a high current, but there's a low current in the branch with two bulbs.

Let's do a check for understanding what is the current flowing through the lower bulbs in the circuit shown? All three bulbs are identical.

Pause the video now look carefully at the circuit, make a choice and then come back to see how you've done.

Welcome back.

If you chose 0.

1 amps, it's correct.

The lower branch has twice as many bulbs, so it'll have twice as much resistance and so only half the amount of current will flow.

Half of 0.

2 amps is 0.

1 amps.

Well done if you've got that right.

We've learned so far that the branch with more bulbs will have a higher resistance and so will have a lower current.

Adding another bulb to this branch will reduce the current even more.

However, the current in the upper branch, this branch here remains the same.

This is because the voltage across that branch will still be the same voltage as before.

Let's do a true false check for understanding.

In the circuit below, if a resistor is added to the lower branch in series, the current flowing through the single bulb will remain at 0.

2 amps.

Is this true or false? Pause the video, look carefully at the circuit, make a choice and then come back to check how you've done.

Welcome back.

If you chose true, that's correct.

The current will remain at 0.

2 amps.

Now's the time to justify your answer.

The choices are A, the voltage across the single bulb branch is still the same, or B, the lower branch has a higher resistance.

Pause the video, look at the statements carefully, make a choice and then come back to see how you've done.

Welcome back.

If you chose statement A, that's correct.

The voltage across a single bulb branch will stay the same, so the current state is the same as well.

The lower branch will have a higher resistance when the resistor is added, but that won't affect the branch above it.

The voltage across that branch will stay the same.

Well done if you got that right.

That was a tricky question.

Parallel circuits have some advantages compared to series circuits.

Let's examine them.

In the parallel circuit, these bulbs each have a higher voltage, 3.

0 volts and so are brighter.

In the series circuit, these bulbs each have a lower voltage because they're sharing it 1.

5 volts and so they'll be dimmer.

Another advantage is if one of the bulbs blows.

If one of the bulbs in the parallel circuit blows, the other will still be lit because it's got its own connections to the cell.

If one of the bulbs in the series circuit blows, it stops the current flowing in the whole circuit because there's a gap in the circuit.

However, more current flows through the electrical cell in the parallel circuit, the electrical cell will run out of energy faster.

In the series circuit, the electrical cell will take longer before it runs out of energy.

Let's do a check for understanding.

Which of these statements is not an advantage of a parallel circuit when compared to a series circuit of two bulbs? The choices are A, if one bulb blows, the other still works in the parallel circuit.

B, the bulbs in the parallel circuit are brighter.

C, a higher current flows through the cell and D, the parallel circuit bulbs get a higher voltage.

Pause the video now, read through the statements carefully, make a choice and then come back to check how you've done.

Welcome back.

If you chose statement C, a higher current flows through the cell.

That's correct.

Well done if you got that right.

You now have a chance to do a practical task to practise what you've learned.

Number one, you're going to build the circuit shown.

It's a parallel circuit with two bulbs.

You're going to measure the voltages across the bulbs and the current through them.

If you have a DC power supply, that'll give you better results.

Once you've done number one, number two, you're going to add another bulb in parallel as shown, and measure the voltages across the bulbs and the currents through them as well.

Pause the video now, carry out the tests and make a note of your results and then come back to see how you've got on.

Welcome back.

Here's a set of example results where the power supply was 1.

5 volts.

In number one, the circuit with two bulbs in parallel.

Both bulbs had 1.

5 volts across them and they had 0.

2 amps running through them.

In number two, the circuit with three bulbs in parallel, each of the bulbs had 1.

5 volts across them and they also had 0.

2 amps across them.

The bulbs always had a voltage of 1.

5 volts across them and a current of 0.

2 amps which flowed through them.

Their brightness was all the same.

Well done if you had a similar set of results.

We're now going to do the third part of this lesson.

Adding branches to a parallel circuit.

An identical bulb can be added to a parallel circuit like the one shown in another branch.

The new bulb and the old ones stay at the same brightness.

This is because the bulbs have the same voltage across them and so will have the same current flowing through them.

If each branch has 0.

2 amps flowing through it, the total current carried will be different.

In the circuit with two bulbs, the total current will be 0.

2 plus 0.

2, which will give us a total current of 0.

4 amps.

In the circuit with three bulbs, the total current is going to be 0.

2 plus 0.

2 plus 0.

2, which will give us 0.

6 amps.

There's a bigger current flowing in the parallel circuit with more branches.

Increasing the number of loops in the circuit causes more current flow through the electrical cell.

The higher current will drain the energy store of the electrical cell more quickly.

Here's a check for understanding.

Is this statement true or false? Adding more loops with bulbs to the circuit shown will not affect the current in the original loops.

Assume the electrical cell works perfectly.

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

Welcome back.

If you chose true, that's correct.

Now's the time to justify your answer.

We have A, each additional loop causes more current to flow in the cell.

Or B, each loop is like a separate series circuit connected directly to the cell.

Pause the video now and then choose the statement that correctly justifies the true answer.

Welcome back.

If you chose statement B, each loop is like a separate series circuit connected directly to the cell.

That's correct.

Each separate series circuit won't affect the original current.

Statement A, is technically correct, but it doesn't justify the true statement.

Well done if you got that right.

Now's your chance to do our practise task.

Andeep and Laura are trying to predict what will happen if they add a branch with three bulbs to this parallel circuit as shown? Andeep says, "Adding the branch with three bulbs will make all the bulbs dimmer." Laura says, "When the branch with three bulbs is added, all the bulbs will be just as bright." Say who is right or wrong, and explain why saying what will happen to the resistance, the current and the voltage.

Pause the video now.

Go ahead and complete the task, and then come back to see how you've done.

Welcome back.

Both Andeep and Laura unfortunately are wrong.

The single bulbs in the original branches will stay at the same brightness, but the three added bulbs will be dimmer.

The current flowing through and the voltage across the single bulb will stay the same.

The current flowing through the branch with three bulbs will be lower, and the voltage will be shared by the three bulbs, so will also be lower.

The total resistance of the circuit will decrease as there is another loop, which means the electrical cell will carry more current.

If you got it right, really well done.

We've reached the end of the lesson, so let's summarise what we've covered.

In a series circuit, the current is the same everywhere in the loop.

Adding components to the loop, will increase the resistance and cause the current to decrease.

Components added in series will share the voltage so each component gets a lower voltage.

In parallel circuits, each branch gets the same voltage and the current flowing through the electrical cell or battery increases.

The energy in the electric cell or battery will run out faster.

Bulbs in parallel circuits are brighter than in series circuits.

And if one bulb blows in a parallel circuit, the others still work.

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