1. Simple Electric Circuits
D. Crowley, 2008

2. Simple Electric Circuits
Thursday, April 20, 2017
Simple Electric Circuits
To be able to draw simple electric circuits and know what happens when more bulbs are added

3. Electricity What is electricity?
Electricity is the flow of electrical power (charge) in the form of electrons
Electricity is a useful secondary energy source – most energy sources (like coal, oil, nuclear, wind etc…) can be converted into electricity
Electricity is the flow of electrons around our electrical circuit

4. Circuits low pressure high pressure boiler and pump radiator radiator
An electric circuit is like the central heating system in a house…
low
pressure
high
pressure
There is a pump which pushes water all around the house
The water everywhere starts to move at the same time
There are pipes which carry the water
In the pipes the water is flowing
When river water moves, we say that a current of water flows - when electric charges move in a wire, we say that an electric current flows
boiler
and
pump
radiator
radiator
flow of
water

5. Circuits
A bulb in the circuit is like a radiator – an electrical device uses electrical energy, supplied by the circuit
The wires are like pipes - they carry the flow of electricity (current) around the circuit (flow of electrons goes from negative to positive)
The electrical current is pushed by the cell (battery) – this is the voltage
Cell + -
Wires
Lamp

6. Electric Circuits An electric current needs two things: -
Something to make the electricity flow (e.g. a battery or power pack)
A complete circuit
Without these two basic things, an electric current will not flow
Cell + -
Wires forming a complete circuit

7. Component Diagrams
Circuit symbols are used to show the components in an electrical circuit (wires are represented by straight lines)
Current – the flow of electricity (flow of electrons) around the circuit
Voltage – the driving force which pushes the current around the circuit
Resistance – anything in the circuit which slows the flow down

8. Component Symbols
A common list of components is shown below – use this to complete the simple electric circuits worksheet

9. Simple Electric Circuits

10. Simple Electric Circuits

11. Switches Switches are used to control components in circuits
In a simple circuit with one switch, the switch controls all the components…

12. Series & Parallel There are two types of circuit – series and parallel
For now, we will concentrate on series circuits – circuits where all the components are connected in a line, end to end
Removing one component breaks the circuit, stopping all the components
Christmas tree lights are often in series, so when one bulb blows, they all stop
They are also used for warning systems, so if a component breaks the light in series will stop, hopefully alerting you

13. Current What is current?
Current is a measure of how much electric charge flows through a circuit (the flow of electrons around a circuit, from negative to positive terminals))
Current is measured in amps – e.g. 20A current is bigger than 5A current
To measure current in a circuit, the ammeter must be placed in series – it does not matter in what order you place this

14. The ammeter can be placed after the components (lamp)
Current
To measure the current, the ammeter must be placed in series (in any order) + -
Ammeter A
The ammeter can be placed after the components (lamp)

15. Or the ammeter can be placed before the component (bulb)
Current
To measure the current, the ammeter must be placed in series (in any order) + -
Ammeter A
Or the ammeter can be placed before the component (bulb)

16. Experiment

17. Experimental Observations
Your first experiment is to find out what happens to the brightness of bulbs when you add more than one to a circuit
Firstly set up a circuit with one bulb in it, and note how bright it is – place the ammeter in different parts of the circuit, testing the current + - + - A A

18. Experimental Observations
Secondly add a second bulb to the circuit and repeat the current test (place it in different positions
Then repeat this with three bulbs in the circuit + - + - + - A A A

19. Experimental Observations
Experiment with three bulbs in the circuit + - A + - + - + - A A A

20. Ammeter Your second experiment is to find the current of each circuit
Reset your circuit to contain just one bulb, and connect the ammeter in series and record the amps reading
Then repeat this with two and three bulbs, recording each current reading + - + - + - 1. 2. 3. A A A

21. Current The current is not used up by the components in a circuit
The current is the same anywhere in a series circuit + -
Current is the same, anywhere in the circuit A A
Current is the same at this point in the circuit, e.g. 1A
Current is the same at this point in the circuit, e.g. 1A

22. Current is always 1A, anywhere in this circuit
Dimmer Bulbs
As more bulbs are added to the circuit they all get dimmer
As more bulbs are added the resistance increases, reducing the flow of current
Having a circuit with many bulbs in it causes a low current, but remember the current is still the same anywhere in this circuit + - + -
Current is always 1A, anywhere in this circuit
Current is reduced in this circuit (more resistance) but it is still always 0.5A, anywhere in this circuit A A

23. Key words: same / decreased / same / not
Current Summary
Circuit 1
Circuit 2 A A A A A
Key words: same / decreased / same / not
Circuit 1 – the current at different positions in the circuit, before and after the lamp was the __________
Current is __________ used by the components in the circuit
Circuit 2 – increasing the number of components in the circuit __________ the current
The current at all points in a series circuit is __________
same
not
decreased
same