1. Year 9 Science
Electricity

2. There are two types of charge: positive and negative.
Electrical Energy
Year 9 Science
Electricity is a form of energy that uses the physical property of charge.
There are two types of charge: positive and negative.
Electrons are very small sub-atomic particles that have a negative charge.
Electricity in wires is a movement of electrons due to a voltage.
This allows electrical energy to be converted into other forms like light, heat and kinetic energy (movement).

3. An electrical current is a flow of charges: usually electrons.
Electrical Energy
Year 9 Science
An electrical current is a flow of charges: usually electrons.
The electrons flow because they are moving down an “energy slope” caused by the voltage.
A voltage gives the electrons energy.
The electrons move, and this movement can do work like lighting a globe.
Scanned probe microscope images of electron flow

4. In order for an electrical current to flow there needs to be:
Electrical Energy
Year 9 Science
In order for an electrical current to flow there needs to be:
charges that are …
… free to move under the influence of …
… a voltage (power supply or battery) through …
a complete (unbroken) pathway.

5. A wired electrical pathway is called a circuit.
Electrical Energy
Year 9 Science
A wired electrical pathway is called a circuit.
If the circuit is unbroken it is said to be a closed circuit and a current can flow.
If the circuit has a gap in it, it is said to be an open circuit and a current cannot flow.
A switch opens and closes a circuit.

6. Electrical Current & Voltage
Year 9 Science
A metal wire is made of atoms.
Each atom has a very small centre called the nucleus.
The nucleus contains protons (+ charge) and neutrons (no charge).
Electrons (- charge) orbit around the nucleus.
The atoms have no overall charge because the number of protons is equal to the number of electrons.
Almost all of any atom is empty space.

7. Electrical Current & Voltage
Year 9 Science
In the metal wire the atoms (nuclei) are locked into position and cannot move but …
… some of the electrons can move from atom to atom and this means they can transfer energy in a circuit.
Metals are good conductors and are said to have a low resistance.
Other materials like plastic and wood do not have free electrons and are poor conductors (insulators).
Insulators are said to have a high resistance.

8. Electrical Current & Voltage
Year 9 Science
Electrical current:
measures the rate of flow of charge
is measured in Amps (Amperes: A) or milliamps (mA)
is measured using an ammeter

9. Electrical Current & Voltage
Year 9 Science
Electrical voltage measures
the amount of energy the charges have (or give up)
is measured in Volts (V) or millivolts (mV).
is measured using a voltmeter
A multimeter is able to measure either voltage or current depending on the setting used.

10. chemical energy → electrical energy
Batteries
Year 9 Science
Batteries are a form of portable electricity that get their energy from a chemical reaction.
chemical energy → electrical energy

11. It has lead plates (electrodes) dipping into an acid electrolyte.
Batteries
Year 9 Science
A car battery is “wet”.
It has lead plates (electrodes) dipping into an acid electrolyte.
A simple torch battery is called a dry cell.
Its electrolyte is a paste so that if the cell is damaged it does not leak so much.
Its electrodes are a zinc cup and a carbon rod.

12. A 1.5V torch battery is really one cell.
Batteries
Year 9 Science
A 1.5V torch battery is really one cell.
Several cells can be joined together to make a battery.
e.g. a 9V battery is really six 1.5V cells. =

13. Different types of cells use different electrodes or electrolytes.
Batteries
Year 9 Science
Normal dry cells cannot be recharged – and their current slowly gets smaller over time.
Different types of cells use different electrodes or electrolytes.
Alkaline cells allow a greater current.
Mercury (button) cells keep a steady voltage for longer but get flat suddenly.

14. Some dry cells can be recharged. Examples are nickel-cadmium cells …
Batteries
Year 9 Science
Some dry cells can be recharged.
Examples are nickel-cadmium cells …
… and lead-acid car batteries.

15. A lead-acid battery consists of six, 2V cells in series connection.
The Lead Acid Battery
Year 9 Science
A lead-acid battery consists of six, 2V cells in series connection.
Each cell has two lead electrodes but one is coated with lead dioxide.
When the battery is being used a chemical reaction converts the lead and lead dioxide to lead sulfate which coats the surface of the two electrodes.

16. The Lead Acid Battery
Year 9 Science
The lead sulfate stays on the electrodes and the chemical reaction can be reversed as the car’s alternaltor recharges the battery while the car is running.
Over time the lead sulfate starts to become harder to convert back and the battery cannot be recharged and needs to be replaced and its parts recycled.

17. Electrode 1. Lead → lead sulfate
The Lead Acid Battery
Year 9 Science
Discharging:
Electrode 1. Lead → lead sulfate
Electrode 2. Lead dioxide → lead sulfate
Charging
Electrode 1. Lead sulfate → lead
Electrode 2. Lead sulfate → lead dioxide

18. They are used in space expeditions but are very expensive.
Fuel Cells
Year 9 Science
Fuel cells are a different cell design that do not need recharging as long as there is a continuing supply of chemicals.
They are used in space expeditions but are very expensive.

19. A torch uses a series connection.
Combining Cells
Year 9 Science
If a circuit needs a higher voltage the cells are connected ‘end to end and positive to negative’ and this is called a series connection.
A torch uses a series connection.

20. Circuit diagrams use symbols to show how a circuit is connected.
Year 9 Science
Circuit diagrams use symbols to show how a circuit is connected.
Straight lines are drawn between circuit components to represent wire connections.

21. Circuit Diagram for a Torch
Year 9 Science
Power supply: two or more 1.5V cells in series
Load: A globe - its filament gets white hot and converts electrical energy into heat and light energy.
Metal strips: act as wires, a switch and a spring (to hold the cells in good contact).

22. Series and Parallel Connections
Year 9 Science
Circuit components (cells, lamps, etc.)may be connected in a line (series) or side to side (parallel).
A series connection provides greater voltage at the same current.

23. Series and Parallel Connections
Year 9 Science
A parallel connection provides greater current at the same voltage.

24. Series and Parallel Connections
Year 9 Science
When globes are connected in series the energy of the electricity is shared among the globes.
The globes glow less brightly.
If one globe is removed this opens the circuit and all globes go out.

25. Series and Parallel Connections
Year 9 Science
When globes are connected in parallel the flow of charge is shared among the globes.
The globes glow do not lose any of
their brightness because the voltage
across each does not change.
If one globe is removed the other
globes do not go out because they
are still connected directly to the
power supply.

26. Moving charges provide current electricity.
Static Electricity
Year 9 Science
Moving charges provide current electricity.
Stationary charges are referred to as static electricity.
Electrons and their negative charge can transfer from object to object due to friction.
An object can become negatively charged by having an excess of electrons.
An object can become positively charged by having a deficiency of electrons.
Like charges repel, unlike charges attract.

27. Materials vary in their attraction for electrons: electron affinity.
Static Electricity
Year 9 Science
Materials vary in their attraction for electrons: electron affinity.
When two objects are rubbed together some electrons will move to the object with greater electron affinity.
The triboelectric series shows the electron affinity of different materials.

28. Static Electricity
Year 9 Science
Most positive (+)
Air
Human Skin
Asbestos
Rabbit fur
Glass
Nylon
Wool
Silk
Aluminium
Paper
Cotton
Wood
Amber
Rubber Balloon
Hard Rubber
Polyester
Polystyrene
Cellophane tape
Polythene
Teflon
Silicone Rubber
Most Negative (-)
When two materials are rubbed together the material that is lower in the series tends to become negatively charged as electrons transfer to it.
The material that is higher in the series tends to become positively charged as electrons transfer from it.

29. Static Electricity
Year 9 Science
Most positive (+)
Air
Human Skin
Asbestos
Rabbit fur
Glass
Nylon
Wool
Silk
Aluminium
Paper
Cotton
Wood
Amber
Rubber Balloon
Hard Rubber
Polyester
Polystyrene
Cellophane tape
Polythene
Teflon
Silicone Rubber
Most Negative (-)
E.g. When a rubber balloon is rubbed with rabbit fur, the balloon becomes charged negatively while the rabbit fur becomes charged positively.

30. State the charge on each object when: Amber is rubbed with wool
Static Electricity
Year 9 Science
Most positive (+)
Air
Human Skin
Asbestos
Rabbit fur
Glass
Nylon
Wool
Silk
Aluminium
Paper
Cotton
Wood
Amber
Rubber Balloon
Hard Rubber
Polyester
Polystyrene
Cellophane tape
Polythene
Teflon
Silicone Rubber
Most Negative (-)
Exercise 1
State the charge on each object when:
Amber is rubbed with wool
Glass is rubbed with silk
Polyester is rubbed with nylon
Exercise 2
For each of the above examples state which material electrons move to and which they move from.

31. Static Electricity
Year 9 Science
An object can become charged negatively by being rubbed by a material that is lower on the tribolelectric series.
If a negatively charged pencil is brought near a piece of paper it can pick it up.

32. This makes the surface of the paper positive.
Static Electricity
Year 9 Science
In this case the negatively charge pencil repels negative charges on the surface of the paper.
This makes the surface of the paper positive.
The negative pencil then attracts the positive surface of the paper.
This principle is used in photocopiers and laser printers.

33. Electrical Quantities
Year 9 Science
A water circuit for a swimming pool is similar to an electrical circuit.

34. Electrical Quantities - Current
Year 9 Science
Electric current is a measure of the amount of electric charge passing a given point every second.
Current is measured using an ammeter and the unit of current is the Ampere (A) or the milliampere (mA).
Ammeters are always connected in series.

35. Electrical Quantities - Current
Year 9 Science
Exercise
What is the reading on the following ammeters: a)

36. Electrical Quantities - Current
Year 9 Science b)

37. Electrical Quantities - Current
Year 9 Science c)

38. Electrical Quantities - Current
Year 9 Science d)

39. Electrical Quantities - Voltage
Year 9 Science
Electrical voltage is a measure of the amount of electrical energy gained or lost by electric charge as it moves through the circuit.
Voltage is measured using an voltmeter and the unit of current is the Volt (V) or the millivolt (mV).
Voltmeters are always connected in parallel.

40. Electrical Quantities - Voltage
Year 9 Science
Exercise
What is the reading on the following voltmeters: a)

41. Electrical Quantities - Voltage
Year 9 Science b)

42. Electrical Quantities - Voltage
Year 9 Science c)

43. Electrical Quantities - Voltage
Year 9 Science d)

44. Electrical Quantities - Resistance
Year 9 Science
Conductors have very little resistance to electric current.
This resistance is still measurable though.
Insulators have a very large resistance.

45. Electrical Quantities - Resistance
Year 9 Science
As electrons move through a circuit they collide with atoms in the wires etc.
This causes them to lose energy.
Electrical resistance is a measure of how difficult it is for electrons to move through a circuit.

46. The volume control on a radio is a variable resistor.
Controlling the Flow
Year 9 Science
Resistors are used in electric circuits to control the voltage and current.
The volume control on a radio is a variable resistor.
Other types are fixed resistances.

47. A variable resistance can be used to control light dimmers.
Controlling the Flow
Year 9 Science
A variable resistance can be used to control light dimmers.
When the resistance in the variable resistor increases the resistance of the whole circuit increases and this reduces the current through the globe.
The amount of energy available to the globe reduces as well – the globe glows less brightly

48. The symbol for a variable resistor can be any of the following:
Controlling the Flow
Year 9 Science
The symbol for a variable resistor can be any of the following:
Exercise 3
Draw a circuit diagram that includes a power supply, a globe, a switch and a variable resistor all connected in series.

49. An electrical current always faces some opposition to its flow.
Controlling the Flow
Year 9 Science
An electrical current always faces some opposition to its flow.
This opposition (resistance) is observed as a heating of components or wires.
If too much current flows through a circuit there is danger of either melting of plastic insulation, sparking and a resulting fire or the melting of components.
In order to prevent this there are two devices that can open a circuit if the current gets too high.

50. Controlling the Flow
Year 9 Science
1. A fuse is a length of low melting point metal alloy of a certain thickness that melts when it gets to a certain temperature produced by a rated current.

51. Circuit breakers are effectively electromagnetic or thermal switches.
Controlling the Flow
Year 9 Science
2. A circuit breaker is a device that disconnects the circuit if the current exceeds a certain rated value. This is a non-destructive way of automatically opening a circuit and may be reset manually.
Circuit breakers are effectively electromagnetic or thermal switches.

52. Measuring the Flow
Year 9 Science

53. Measuring the Flow
Year 9 Science
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Year 9 Science
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Year 9 Science
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Year 9 Science
9126

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Year 9 Science
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58. Measuring the Flow
Year 9 Science
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Year 9 Science
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60. Measuring the Flow
Year 9 Science
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61. Measuring the Flow
Year 9 Science
5561

62. Measuring the Flow
Year 9 Science
3336

63. The energy can be used quickly or slowly.
Electrical Power
Year 9 Science
Electricity is a means off supplying energy that can be used for various purposes.
The energy can be used quickly or slowly.
Power is a measure of how quickly energy is converted from one form to another.
Power is measured in Watts (W) or kilowatts (1000W).

64. The energy can be used quickly or slowly.
Electrical Power
Year 9 Science
Electricity is a means off supplying energy that can be used for various purposes.
The energy can be used quickly or slowly.

65. What is this in kilowatts?
Electrical Power
Year 9 Science
In a circuit the power can be determined by multiplying the current by the voltage.
Exercise 4
Determine the power of an electrical heater that operates at a voltage of 240V and a current of 5A.
What is this in kilowatts?
If the heater was switched to its highest setting of 2400W, what current would it draw?

66. To do
Year 9 Science

67. Controlling the Flow
Year 9 Science
Resistance is measured in Ohms () and is related to voltage and current by Ohm’s Law:
Example 1
A torch globe carrying a current of 200mA with a voltage drop of 3 volts has a resistance of:

68. Controlling the Flow Example 2
Year 9 Science
Example 2
An appliance carrying a current of 4A with a voltage drop of 240V, has a resistance of:

69. Controlling the Flow Exercise 4
Year 9 Science
Exercise 4
A globe carries a current of 2A when a voltage of 6V is applied. Determine the resistance of the globe.
Exercise 5
A length of conductor has a resistance of 5. What current will flow through the conductor when a voltage of 10V is applied?
Exercise 6
An electrical motor carries a current of 4A and has a resistance of 62.5. What voltage exists across the motor?

70. Reading an electricity meter Electrical power Globe wattage
To do
Year 9 Science
Circuit breakers
Reading an electricity meter
Electrical power
Globe wattage