Adding or removing components
In this topic you will:
- find out what happens to current when you add more cells in a circuit
- find out what happens to current when you add more lamps in a circuit
Key words
- adding components
- dimmer
- position
- removing components
Current in a series circuit
If you did Think like a scientist: Making predictions about current in Topic 9.3, you may remember that current is the same all the way around a series circuit.
You can think of the electrons in a series circuit like a train. All parts of the train move at the same speed on the track. The back of the train cannot go faster than the front of the train. As soon as one part of the train moves, all of the train will move.
Electrons flow at the same speed in the wires of a series circuit. When electrons start to flow in one part of the circuit, they all start to flow.
That means you can put an ammeter at any position in a series circuit and it will give the same result.
It also means that you can put the same components of a series circuit in a different order and the current will be the same.
Adding components or removing components will affect the current. The effect depends on what components are changed.
Adding or removing cells
You saw in Topic 3.5 that cells and batteries are stores of chemical energy. In a complete circuit, the chemical energy gets changed to electrical energy.
That means if you add more cells to a circuit, you have more chemical energy to change into electrical energy in the circuit.
Look at the two circuits. Each component is identical in both circuits.
The circuit with two cells has double the electrical energy of the circuit with one cell.
The lamp will be brighter.
The ammeter in the circuit with two cells shows that the current is doubled.
Quick Fact
In a series circuit, the current stays the same throughout. Adding more cells increases the total energy available, which increases current and makes bulbs brighter.
You need to be careful adding more cells to a circuit. The lamps can be damaged and the wires can get hot.
Adding more cells increases the current when the other components are kept the same.
Removing cells decreases the current when the other components are kept the same.
Adding or removing lamps
You saw in Topic 3.5 that lamps change electrical energy to light energy and thermal energy.
Electrons carry electrical energy around a circuit. When the electrons pass through a lamp, the electrons transfer some of their electrical energy to the lamp. The lamp changes the electrical energy into light energy and thermal energy.
Remember that the current is the same at all positions in a series circuit. Putting a lamp in a circuit will make the electrons move more slowly, but they move more slowly the whole way around the circuit.
The circuit with two lamps transfers twice as much energy as the circuit with one lamp. The lamps will be dimmer. That means they do not shine as brightly.
This makes the electrons move at half the speed, so the reading on the ammeter is halved.
Adding more lamps decreases the current when the other components are kept the same.
Removing lamps increases the current when the other components are kept the same.
Questions
Write the letter.
- A Current decreases around the circuit.
- B Current increases around the circuit.
- C Current stays the same around the circuit.
- D Current increases and decreases around the circuit.
Show Answer
C Current stays the same around the circuit in a series circuit.
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B has a larger current.
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Circuit B has more cells, so there is more electrical energy, resulting in greater current.
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C has a larger current.
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Circuit C has fewer lamps, so there is less resistance, which increases the current.
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Add more cells or remove one of the lamps to reduce resistance.
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Add another lamp to increase resistance, or remove a cell to reduce the voltage.
Think Like a Scientist
In this task, you will measure current in circuits when components are added and removed.
You will need (for each group):
- 3 cells
- 3 lamps
- an ammeter
- wires
- a switch
Safety
You must avoid damage to components where possible. Follow these rules:
- Do not remove all the lamps from a circuit, leaving only the cells.
- Do not connect an ammeter directly to cells without lamps.
- If a lamp appears too bright, switch off immediately.
Part 1 – Varying number of lamps
- Build this circuit.
- Close the switch and record the current.
- Add another lamp.
- Record the current with two lamps.
- Repeat with three lamps.
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Use a table or bar chart showing number of lamps vs current (A).
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Insert a chart or table appropriate to the recorded values.
Part 2 – Varying number of cells
- Build this circuit.
- Close the switch and record the current.
- Repeat with two and then three cells.
- Display your results in an appropriate way.
Show Answer
Adding more lamps decreases the current. Adding more cells increases the current. This shows how load and supply affect total current.
Show Answer
Lamp brightness and resistance may vary slightly. Measurement precision may be limited by the ammeter resolution or contact quality.