Sectieoverzicht
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Series circuits
In a television series, you get several episodes, one after the other. A series circuit is similar. You get several components one after the other.
If you follow the circuit diagram from one side of the cell to the other, you should pass through all the different components, one after the other, without any branches.
If you put more lamps into a series circuit, the lamps will be dimmer than before.
In a series circuit, if a lamp breaks or a component is disconnected, the circuit is broken/ incomplete, and all the components stop working.
Series circuits are useful if you want a warning that one of the components in the circuit has failed. They also use less wiring than parallel circuits.
Current in a series circuit
Current is a measure of how much electric charge flows through a circuit. The more charge that flows, the bigger the current.
Current is measured in units called amps. The symbol for amps is A. For example, 20A is a bigger current than 5A.
A device called an ammeter is used to measure current. Some types of ammeter have a pointer on a dial, but most have a digital readout. To measure the current flowing through a component in a circuit, you must connect the ammeter in series with it.
The current is the same everywhere in a series circuit. It does not matter where you put the ammeter, it will give you the same reading.
All three ammeters give the same reading in this series circuit.
Adding more cells
The current in a series circuit depends upon the number of cells. The more cells you add, the greater the current.
The more cells, the greater the current.
Current is not used up
You might think that the current gets less as it flows through one component after another. But it is not like this. The current is not used up by the components in a circuit. This means that the current is the same everywhere in a series circuit, even if it has lots of lamps or other components.
The current is the same everywhere in a series circuit.
There are two types of circuits we can make, called series and parallel.
The components in a circuit are joined by wires.
• if there are no branches then it's a series circuit
• if there are branches it's a parallel circuit
Components in a circuit will resist current; components slow the current down. So the more components in a circuit, the slower the current will be.
Parallel circuits
In parallel circuits different components are connected on different branches of the wire. If you follow the circuit diagram from one side of the cell to the other, you can only pass through all the different components if you follow all the branches.
In a parallel circuit, if a lamp breaks or a component is disconnected from one parallel wire, the components on different branches keep working. And, unlike a series circuit, the lamps stay bright if you add more lamps in parallel.
Parallel circuits are useful if you want everything to work, even if one component has failed. This is why our homes are wired up with parallel circuits.
Current in a parallel circuit
The current in a parallel circuit splits into different branches then combines again before it goes back into the supply. When the current splits, the current in each branch after the split adds up to the same as the current just before the split.
When the current splits along different branches, the proportion which travels along each branch is inversely proportional to the resistance one the branch. The higher the resistance on the branch, the less current will flow on that branch and visa versa.
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Investigating current in a series circuit
1. Copy the following table into your notebook:
Number of batteries
Number of bulbs
Current (amps)
1
1
1
2
1
3
3
1
3
2
3
3
2. Click on the link below:
https://phet.colorado.edu/sims/html/circuit-construction-kit-ac-virtual-lab/latest/circuit-construction-kit-ac-virtual-lab_en.html
3. Using the Phet simulation, build the following circuits, noting the ammeter readings in your table.
What do you notice about the current in the circuits?
How does changing the number of bulbs affect the current?
How does changing the number of batteries affect the current?
Conclusion:
The first point to note is that in a series circuit, the ammeter reading on both ammeters will be the same. This is because the current only has one path to travel. At any point in a series circuit, the current will be the same.
Increasing the number of bulbs in a circuit increases the resistance in a circuit and will slow the current down causing you to note a lower reading on each ammeter.
Increasing the batteries, has the effect of reducing the resistance, so the current will travel faster round the circuit causing you to note a higher reading on the ammeters. -
Investigating current in a parallel circuit
1. Click on the link below:
2. Build a parallel circuit as shown in the picture below:
2. Close the switch. What do you notice about the brightness of the bulbs? Are they equally bright?
What do you notice about the ammeter readings which are alongside each bulb?
Are they the same?
If you add them together, do they add up to the ammeter readings of the current entering and leaving the circuit?
Hint: they should!
Conclusion:
If you add the ammeter readings on the two branches:
2.70 + 2.70 = 5.40 A which is the same as the current entering and leaving the circuit.
Both bulbs are equally bright and have the same amount of current flowing through them. This is because they are resisting the current equally.
3. Remove the bulb from the first branch of the circuit. Is the bulb on the second branch still lit? What do you notice about the ammeter reading next to the bulb?
4. Open the switch. Replace the bulb, and add another branch to the circuit, with 2 bulbs and an ammeter.
5. Close the switch. What do you notice about the brightness of the bulbs? Are they equally bright?
What do you notice about the ammeter readings which are alongside each bulb?
Are they the same?
If you add them together, do they add up to the ammeter readings of the current entering and leaving the circuit?
Hint: they should!
Conclusion:
If you add the 3 ammeters together from the picture below:
2.70 +2.70 + 1.35 = 6.75 A, which is equal to the current entering and leaving the circuit.
The brightness of the bulbs and the ammeter reading of the branch added are not the same is the other two branches. This is because there are two bulbs sharing the circuit, which increases the resistance and reduces the speed of the current.
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