1. Static
Circuits
Mains
Electricity

2. Objectives
Identify common materials which are electrical conductors or insulators, including metals and plastics.
Explain how insulating materials can be charged by friction.
Recall that there are forces of attraction between unlike charges and forces of repulsion between like charges.

3. Electric Charge Atoms are made of protons, neutrons, and electrons.
The electrons have a negative electric charge.

4. Static Electric Charge
Electrons can be transferred from one material to another. - - + + - + - - - + + - + - + - + - + - + - + - + - + - + - + - + - + +
+ve charge
-ve charge

5. Static Electric Charge
Opposite charges attract.
Like charges repel. + - + + - -

6. Electrostatic Phenomena
Acetate Rods
Polythene Rods - + - - + - - + - + + + - + - - + - - + - + + + - + - + - - + - + - - + - - + - - + - + + - + + - + + + - + - + - - + - + - - + - - + - - + - + - + + - + + + + - + - - + - - + - + + +
Cloth
+ve charge - + -
Cloth
-ve charge - + - - + - + + +
Acetate Rod
+ve charge
Polythene Rod
-ve charge

7. Electrostatic Phenomena
Why do electrically charged balloons stick on the wall?

8. Electrostatic Phenomena
Why do electrically charged combs pick up pieces of paper?

9. Objectives
Explain electrostatic phenomena in terms of the movement of electrons.
Recall the potential dangers of electrostatic charges, e.g. when fuelling aircraft and tankers.
Recall some uses of electrostatic charges, e.g. in photocopiers and inkjet printers.

10. Dangers of Static

11. Uses of Static

12. Uses of Electrostatics
Spray Painting.

13. Uses of Electrostatics
Inkjet Printers

14. Uses of Electrostatics
Photocopiers
See ActiveBook Animation

15. Uses of Electrostatics
Electrostatic Precipitators

16. Uses of Electrostatics
Electrostatic Precipitators
Smoke With Dust
Particles Removed
Earthed Metal
Plates -
Smoke & Charged
Dust Particles - - - - - -
Metal Mesh V
Smoke & Dust
Particles

17. The Gold Leaf Electroscope
Use to detect charge.
Gold leaf is extremely thin and able to move.
Metal
Plate
Gold
Leaf
Metal
Rod

18. The Gold Leaf Electroscope+ + - + - + - + - + - - - + + - - + - - + +

19. The Gold Leaf Electroscope+ + - + - + - - - + - - + - - + + + + - + -

20. Can you correct his mistakes?
Chris’s Homework
Atoms contain neutrons and two charged particles, protons (negative) and electrons (positive). Conductors can be ‘charged by friction,’ a process where one material loses protons to another material.
Like charges attract, and opposite charges repel.
Aeroplanes have to be earthed to ensure there is no static charge around when they are refuelling.
Uses of static electricity include laser printers, photocopiers, and setting fire to F1 drivers.
Can you correct his mistakes?

21. Learning Objectives Identify common circuit symbols.
Identify electric current as a flow of charge/electrons.
Explain how current behaves in series and parallel circuit.

22. Circuit Symbols Cell Battery Bulb Resistor Ammeter Voltmeter Switch
LDR
Thermistor
Variable
Resistor
Fuse

23. (Two or More ‘Branches’)
Series and Parallel
Series
(One Complete Loop)
Parallel
(Two or More ‘Branches’)

24. Electrical Current
Electrical current is the flow of electrical charge.
The charge comes from the electrons.

25. Electrical Current Electrons flow around the circuit.
They gain energy from the cell, and transfer energy to other components.
Inside Circuits

26. Measuring Current Ammeters must be placed in series.
They need to measure the current flowing through them.

27. Electrical Current A2
1 A A1

28. Electrical Current
4 A A3 A1 A2

29. Electrical Current
6 A A4 A1 A2 A3

30. Electrical Current
3 A A3 A1 A2

31. Learning Objectives Define current as the rate of flow of charge.
Identify electrons as the charge carriers in electrical circuits.
Identify, use, and explain the equation I = Q/t.

32. Electrical Charge
Protons and electrons both have electrical charge (positive and negative).
Charge is measured in coulombs, C.
One coulomb of charge is the equivalent of 6.25 billion billion electrons!
( )
Charge has the symbol Q.

33. Electrical Current
Current is the rate of flow of charge (how much charge flows in a certain time).
Current is measured in amps.
One amp is equal to one coulomb of charge passing a point every second.
Current = Charge / Time Taken
I = Q / t

34. Electrical Current Questions I = Q / t
10 C of charge pass a point in 5 seconds. What is the current?
A current of 3 A flows for 10 seconds. How much charge flowed past each point?
How long will it take for a 100 C of charge to flow past a point when the current is 2 A?

35. Electrical Current
The ______ in a circuit is a measure of how much ________ is flowing.
Current is measured in ____.
A higher current means more ______ is flowing past a point every ______.
A current of one amp equals one _______ of charge flowing past a point every second.
The total current entering a ______ must _____ the total current _______ a junction.
Words: second junction exiting current charge amps equal electricity coulomb

36. Learning Objectives Explain the term ‘Potential Difference.’
Explain how potential difference behaves in series and parallel circuits.

37. Potential Difference
Initial GPE
Potential
Difference
Final GPE

38. Potential Difference
0 V
1.5 V pd
0 V
1.5 V

39. Recording Potential Difference

40. Investigating Potential Difference
You will need:
2 x Cells.
3 x Bulbs.
10 x Connecting Wires.

41. Investigating Potential Difference
Series
Parallel

42. Investigating Potential Difference
Back

43. Investigating Potential Difference
Back

44. Potential Difference 100 J 80 J 60 J 40 J 20 J 20 J 20 J -20 J -20 Jpd pd pd
20 J
20 J
20 J

45. Potential Difference 100 J 80 J 60 J 40 J 20 J 20 J 20 J 0 V 0.5 Vpd pd pd
0 V
0.5 V
0.5 V
1.0 V
1.0 V
1.5 V

46. Potential Difference
1.5 V

47. Potential Difference
1.5 V

48. Potential Difference
1.5 V
1.5 V

49. Potential Difference
3 V
3 V

50. Potential Difference
9 V
4.5 V

51. Potential Difference
3 V
3 V

52. Potential Difference
1.5 V

53. Potential Difference
1.5 V

54. Potential Difference
1.5 V

55. Potential Difference
The _________ _________ of a component is a measure of how much _____ is _________ in the component.
The potential difference across the ____ must _____ the ___ of the potential differences across the components in a ______ circuit.
Words: series cell transferred energy equal sum potential difference

56. Current & pd Summary is equal splits up In a series circuit:
Current _________ at any point.
Potential difference _________ over each component.
In a parallel circuit:
Current __________ down each branch.
Potential difference ________ across each branch.
is equal
splits up

57. Learning Objectives
Identify that an increase in resistance will reduce the electrical current.
Explain how the resistance of LDRs and thermistors change with light intensity and temperature.
Determine Ohm’s Law.

58. Resistance Which of these materials will have the highest resistance?
Wood
Metal

59. Add a second bulb and record the new current.
Resistance
You will need:
two cells.
two bulbs.
a multimeter.
5 connecting wires.
Connect this circuit and record the current:
Add a second bulb and record the new current. A

60. Resistance
Resistance is anything that will resist a current; i.e. it makes it harder for electricity to flow.
It is measured in ohms, Ω.
It has the symbol R.

61. Resistance
All components in electrical circuits have ________ – even the ____!
Some components, like _____, have a ____ resistance. The ____ wire in the _______ makes it harder for the current to flow.
Putting more bulbs in _____ will increase the resistance and ______ the current.
Words: resistance increase thick thin decrease filament series high low wires bulbs

62. Measuring Small Currents
Milliammeters must be placed in series.
They need to measure the current flowing through them.

63. Diodes
A diode only lets ________ flow in one __________ – it has very high __________ in the other direction.
0.6 V
Words: direction current resistance

64. Light Dependent Resistors
Light dependent resistors (____) have a ____ resistance in the dark. When _____ shines on the LDR it has a ___ resistance. This makes it easier for _______ to flow.
Words: high current LDRs
low light

65. Thermistors
Thermistors have a ____ resistance when they are cold. When they ____ up they have a ___ resistance, making it easier for current to flow. The increase in ___________ increases the number of free _________ available.
Words: high current heat
low electrons temperature

66. Thermistor – resistance DECREASES when temperature INCREASES
Comparison
Light dependant resistor – resistance DECREASES when light intensity INCREASES
Thermistor – resistance DECREASES when temperature INCREASES
Resistance
Amount of light
Resistance
Temperature

67. Straight Line Graphs 6 6 Gradient = Rise / Run Gradient = 6 / 6

68. Straight Line Graphs 12 6 Gradient = Rise / Run Gradient = 12 / 6

69. Straight Line Graphs 3 6 Gradient = Rise / Run Gradient = 3 / 6

70. Resistance
I.e. If you double the potential difference, the current doubles
The graph shows that current is directly proportional to potential difference.
This is known as Ohm’s Law.

71. Resistance General equation for a straight line graph is: y = mx + c.
y = Voltage (V) x = Current (I) m = Gradient
The gradient is also equal to the resistance (R).
Therefore, V = IR

72. Resistance Questions V = IR What is the resistance of the following:
A bulb with a voltage of 3 V and a current of 1 A.
A resistor with a voltage of 12 V and a current of 3 A
A diode with a voltage of 240 V and a current of 40 A
A thermistor with a current of 0.5 A and a voltage of 10 V

73. Learning Objectives Identify the unknown resistance of a resistor.
Plot and explain the Current/Potential Difference graph for a filament bulb.

74. Mystery Resistance!
Calculate the resistance of one of the resistors.

75. Filament Bulbs
3 V A V

76. Resistance
As the wire heats up the resistance increases.

77. Filament Bulbs
As voltage increases the bulb gets hotter and resistance increases

78. Filament Bulbs
Be aware...

79. Learning Objectives
Explain the difference between conventional current and electron flow.
Plot and explain the Current/Potential Difference graph for a diode.

80. Diodes
5 V mA V

81. Resistance of a Wire
Plan an experiment to find the resistance of a wire.
Apparatus.
Circuit diagram.
Safety precautions (voltage?).
What measurements will you take?
What will you do with your results?
How will you know if it is an ohmic conductor?

82. Mains Electricity
To consumer unit

83. Mains Electricity Earth wire Live wire Fuse Neutral wire Cable grip
Insulation

84. Mains Electricity
The live wire has alternating current (AC) flowing through it.
The neutral wire completes the circuit.
Earth wire
Neutral wire
Insulation
Live wire
Fuse
Cable grip

85. Mains Electricity
The earth wire is a safety device. There is usually no current flowing through it unless an appliance develops a fault.
Earth wire
Neutral wire
Insulation
Live wire
Fuse
Cable grip

86. Mains Electricity

87. Mains Electricity

88. Mains Electricity

89. Mains Electricity

90. Mains Electricity

91. Mains Electricity

92. Mains Electricity

93. The Earth and Fuse Wires
Write a short paragraph explaining:
Which wires the mains electricity usually flows through.
What happens to the circuit when the live wire is damaged.
What happens to the resistance of the circuit.
What happens to the current.
What happens to the fuse wire.

94. Can you correct his mistakes?
Chris’s Homework
Cables for mains electricity have three wires; positive, negative, and earth. The current usually flows through all three wires in series. If the live wire becomes connected to the casing of an appliance the current no longer flows through the earth wire. This reduces the resistance of the circuit and causes more current to flow. The increased current causes the fuse wire to melt, breaking the circuit.
Can you correct his mistakes?

95. Mains Electricity

96. Hazards

97. V
DC stands for “Direct Current” – the current only flows in one direction:
Time
1/50th s
AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz)
230V T V

98. Alternating Current

99. Power

100. Power = Current x Potential Difference
A watt is a unit of power.
Power is defined as the amount of energy transferred per unit time.
I.e. It is the amount of energy transferred each second
One watt is equal to one joule per second.
I.e. 1 W = 1 J/s
Power = Current x Potential Difference

101. Power = Current x Potential Difference
P = I x V
J C J C J
_ _ _ ___
= x =
s s C C s

102. Power If we know two of the three values we can work out the third.
For mains electricity in the UK the voltage is 240V.
The power rating is often shown; i.e. a 60W bulb or a 1.2kW kettle.
We can therefore calculate the current flowing through the appliance.

103. Challenge
Use the information provided on the appliances to calculate the unknown.
For example, if the appliance has a power rating (i.e. You know how many watts it uses) and a voltage rating, you can calculate the current.
Record your calculations in your notes.

104. Questions P = IV Copy and complete the table. Appliance
Power rating (W)
Voltage (V)
Current needed (A)
Fuse needed (3, 5 or 13A)
Toaster
960
240
Fire
2000
Hairdryer
300
Hoover
1000
Computer
100
Stereo 80

105. Energy & Power
If the power is the amount of energy transferred every second, the total energy will be:
Energy = Power x Time
E = P x t
Example: If a 1200W kettle is used for 3 minutes, what is the total energy transferred?
A. E = P x t
= 1200 W x 180 s
= 216,000 J or 216 kJ

106. Questions
What is the power rating of a light bulb that transfers 120 J of energy in 2 seconds?
What is the power of an electric fire that transfers 10,000 J of energy in 5 seconds?
How much energy does a 150W light bulb transfer in
a) one second, b) one minute?

107. Energy = Current x Potential Difference x Time
Energy & Power
Since power = current x potential difference:
Energy = Power x Time
Energy = Current x Potential Difference x Time
E = I x V x t
Example: How much energy is transferred to a 1.5 V bulb if a current of 1 amp flows for 10 seconds?
A. E = I x V x t
= 1 A x 1.5 V x 10 s
= 15 J

108. Questions
How much energy is transferred to a 12 V bulb when a current of 2 A flows for 30 seconds?
How much energy is transferred to a 24 V bulb when a current of 4 A flows for 40 seconds?
How much energy is transferred to a 12 V bulb when a current of 2 A flows for 2 minutes?

109. Revision – 2.10
1 A
2 A
3 A
4 A

110. Revision – 2.10
1 A
0.5 A
1 A
2 A
10 Ω
5 Ω