3. Early experiments with electricity
Benjamin Franklin was a scientist in the 18th century.
He carried out many experiments with electricity, including this one.
Franklin proved the link between lightning and electricity using a kite attached to a metal key.
Don’t try this at home!

4. What is an electrical circuit?
An electrical circuit is like a central heating system:
There is a pump that pushes water around the system.
The water everywhere starts to move at the same time.
There are pipes that carry the water.
The water flows through the pipes.

5. What is an electrical circuit?
Worksheet 1 accompanies this slide.

6. Drawing electrical circuits
Scientists don’t draw circuits as they look in real life. This is because it takes too long and each person would draw something slightly different.
Instead, they use circuit symbols to represent each component in the circuit. They are drawn exactly the same way each time!
Wires are drawn as straight lines. They don’t have to represent the real lengths of the wires.

7. Match the circuit symbols

8. Components in an electrical circuit

10. What is a series circuit?
This is a simple series circuit.
In a simple series circuit, everything is connected in one loop across the terminals of the battery. There are no points where the current can split
or join (these are called junctions).
This circuit has two lamps connected in series. Circuits are always drawn using straight lines.

11. Examples of series circuits
Here are some other simple series circuits:
Two resistors connected in series.
A variable resistor (or rheostat) and a bulb connected in series.

12. Measuring current
The unit of measurement for current is the amp, which has the symbol A.
Current is measured using a device called an ammeter.
In a circuit diagram, an ammeter is shown by an ‘A’ in a circle.
When measuring the current through a component, the ammeter is always connected in series (in the same loop) with that component.

13. Experiment 1: current in a series circuit

14. Current in a series circuit: summary

15. Measuring voltage
Voltage is measured using a device called a voltmeter.
In a circuit diagram, a voltmeter is given the symbol V.
When measuring the voltage across a component, the voltmeter is always connected in parallel with (or across) the component.
This is still a series circuit, as the voltmeter does not affect the circuit.
The voltage supplied by the battery is shared between all the components in a series circuit.

16. Experiment 2: voltage in a series circuit

17. Voltage in a series circuit: summary

18. Current or voltage?

19. Experiment 3: cells in a series circuit

20. Cells in a series circuit: summary

21. Series circuits – key ideas
In a series circuit the current is the same in all parts of the circuit. Series circuits are found in torches and strings of Christmas lights.
The supply voltage is shared between the components in a series circuit. (The sum of the voltage across each component is the same as the total supply voltage.)
The current depends on the voltage in any circuit.

22. Make your own series circuit

23. Series circuits: summary

25. What is a parallel circuit?
A parallel circuit is one that contains a point (a junction) where the current can split (point A) or join (point B).
This means that there is more than one path around the circuit. A B

26. Modelling parallel circuits

27. Measuring current in a parallel circuit
Set up the circuit as shown.
Place an ammeter, in turn, at positions 1, 2, 3 and 4 and record the readings in a table.
Current (A) A1 A2 A3 A4
Ammeter

28. Current in a parallel circuit
In a parallel circuit, the current that leaves the cell is the same as the current that returns to the cell.
The ammeter readings for A1 and A4 should be the same.
This is because the current does not get used up by the circuit, just the energy that the current is carrying.

29. Current in a parallel circuit
The current splits up at the first junction and then joins together at the second junction.
The following is always true for this type of parallel circuit:
A1 = (A2 + A3) = A4
If the bulbs are identical, then the current will split evenly. If the bulbs are not identical, then the current will not split evenly.

30. Measuring voltage in a parallel circuit
Connect up this circuit and measure, in turn, the voltage at V1, V2 and V3. Record your results in the table.
Voltage (V) V1 V2 V3
Voltmeter
What do you notice about the results?
How can you explain this?

31. Make your own parallel circuit

32. Cells in a parallel circuit: summary

33. Series and parallel circuits: summary
Worksheet 2 accompanies this slide.
The worksheet involves a simple role play to model a circuit.

35. Glossary Glossary: ammeter – A device that measures electric current.
circuit – A complete loop of conducting components that electricity flows around.
current – The flow of electricity, measured in amps (A).
model – a scenario used by scientists to develop theories and explain scientific ideas.
parallel – A branched circuit – it has components connected on separate branches.
resistor – A component that makes it difficult for electricity to flow and so reduces the current.
series – A circuit without any branches – it has components connected in a row.
supply voltage – The amount of ‘push’ that a cell gives a circuit, measured in volts.
voltage – The amount of ‘push’ that a cell gives a circuit, or that a circuit component uses up, measured in volts (V).
voltmeter – A device that measures voltage.

36. Anagrams

37. Multiple-choice quiz

38. True or false?