1. Electronics
“the science that deals with the control of electrons in an electrical circuit or system”
16th Jan

2. Electronics around us

3. Key words: energy conversions / transformations, input devices,
microphone, solar cell, thermocouple
By the end of this lesson you will be able to:
Describe the energy transformations involved in
the following devices: microphone,
thermocouple, solar cell.
State that the resistance of a thermistor
usually decreases with increasing temperature,
and the resistance of an LDR decreases with
increasing light intensity.
Carry out calculations involving V=IR for the
thermistor and LDR.
18th December / 8th / 9th January

4. Electronic Systems A useful system can change one thing into another.
Put a coin in and you get a can of drink out.

5. The iron changes electricity to heat.

6. The Black Box
In electronics we think about the process as a “black box”
We use a block diagram to represent the system.

7. The Toaster as an electronic system

8. Radio Receiver

9. Electronic Thermometer

10. All electronic systems need electrical
signals to work.
At the input stage we need to convert a
form of energy into an electrical signal.
At the output stage we need to convert
the electrical signal into another form of
energy.

11. Battery operated torch

12. Microphone
converts sound energy into electrical energy
Amplifier
amplifies the weak electrical signal
Loudspeaker
converts electrical energy into sound energy

13. Digital and Analogue Signals
There are two types of signals
used by electronic systems:
analogue and digital.

14. …can have only 2 values, 1 or 0
A digital signal.. 1
…can have only 2 values, 1 or 0

15. An analogue signal...
…can have any value

16. Analogue Signals
Continuous range of values

17. Digital Signals Only two possible values Maximum (logic ‘1’ or high)
Minimum (logic ‘0’ or low)

18. Digital vs Analogue Digital signals carry more information per
second than analogue signals.
Digital signals maintain their quality over
distance far better than analogue signals.

19. Input Devices
An input device converts
some form of energy into an
electrical signal.

20. The microphone as an input device
What is the energy change which takes place in a microphone?
The microphone converts sound energy into an electrical signal.
Everyday uses of microphones?

21. Thermocouple What is the energy change which takes
place in the thermocouple?
The thermocouple converts heat energy
into an electrical signal.

22. Thermocouple The sensitivity of the thermocouple is 40 µV / °C.
For every degree above room
temperature the voltmeter reading
increases by V

23. Thermocouple The hotter the temperature the higher
the reading on the voltmeter.
The colder the temperature the lower the
reading on the voltmeter.

24. Thermocouple The largest voltage reached was mV.
To convert to V we divide by 1000:

25. Thermocouple
Added to room temperature of 23 °C means the highest temperature is

26. The Solar Cell A solar cell converts light (solar) energy into
an electrical signal.

27. The Solar Cell Solar Cell As brighter light shines on the solar
Voltmeter
As brighter light
shines on the solar
cell, what happens to
the voltage output?

28. Light Dependent Resistor
We find that increasing light intensity causes an LDR’s resistance to decrease.
Light Up
Resistance
Down
LURD

29. Temperature Up Resistance Down
Thermistor
We find that heating a thermistor causes its resistance to decrease.
Temperature Up Resistance Down

30. Ohm’s Law V I R

31. Review Ohm’s Law calculations involving LDRs and Thermistors.
Input devices questions.

32. What have I learned today?

33. By the end of this lesson you will be able to:
Key words: energy conversions / transformations,
output devices, light emitting diodes (LED)
By the end of this lesson you will be able to:
Give examples of output devices and the energy
conversions involved.
Draw and identify the symbol for an LED.
State that an LED will light only if connected one
way round. Describe by means of a diagram a
circuit which will allow an LED to light.
Calculate the value of the series resistor for an
LED and explain the need for this resistor.
17th January

34. Output Devices kinetic energy The electric motor converts electrical
energy into
kinetic energy

35. Output Devices
The relay switch is a magnetically
operated switch.

36. The Relay Switch Explain the purpose of a relay switch:
The relay switch is a switch operated by
an electromagnet. It allows switching of a
circuit with a high current by closing a
switch in a circuit with a low current.

37. The Relay Switch Explain how the relay works:
When the switch in the circuit with the low
voltage supply is closed, the current through
the coil of wire creates a magnetic field. This
closes the switch contact in the second
circuit, completing the second circuit and
allowing the motor to operate.
Crocodile Physics [relay model]
Virtual Int 2 Physics -> Electricity and Electronics -> Electronic Components -> Output Devices

38. The Light Emitting Diode (LED)
The LED is an output device which
changes electrical energy into
light
DON’T CONFUSE IT WITH AN LDR!

39. LED
A filament lamp and an LED are normally used for different purposes.
Where might an LED be used?

40. LED
What are the differences between the lamp and the LED?
The LED does not light if the connections to the d.c. power supply are reversed. It requires only a small current to operate. It is a digital output device i.e. on or off.
What are the advantages of the LED over a filament lamp?
The LED requires only a small current to operate. It does not get hot in operation.

41. Using a resistor in series with an LED
Why is it necessary to use a resistor in
series with an LED?
The resistor is required to limit the
current to avoid destroying the junction
of the LED.

42. Will this LED light?

43. YES!

44. Will this LED light?

45. YES!

46. Will this LED light?

47. YES!
It doesn’t matter where the resistor is!

48. But…will this LED light?

49. NO!

50. Will this LED light?

51. but if the LED is “facing the wrong way” it will not light!
It doesn’t matter where the resistor is…
but if the LED is “facing the wrong way” it will not light!

52. Connecting an LED An LED will work only is connected to the
power supply the right way round.
In a circuit diagram, the arrow of the
diode must be pointing towards the
negative connection of the battery.

53. What about…this LED?

54. Oops – you’ve blown it up!
Will this LED light?
Oops – you’ve blown it up!

55. Series Resistor and LEDs
Virtual Int 2 Physics -> Electricity &
Electronics -> Electronic Components ->
Series Resistor for an LED

56. Calculating value of series resistor required - example
The maximum voltage across an LED is
2.3 V. The current through it must not
exceed 10 mA. The LED is connected to a
5 V supply. Calculate the value of the
resistor R, connected in series with the
LED.

57. What about…this LED?

58. VS = VLED + VR Since the LED and resistor are in series, what
can we say about the voltage?
VS = VLED + VR
and the current?
the current through each component is the
same (10 mA = A)

59. VS = VLED + VR Since the LED and resistor are in series, what
can we say about the voltage?
VS = VLED + VR
and the current?
the current through each component is the
same (10 mA = A)
supply voltage
voltage across the resistor
voltage across the LED

61. Calculating value of series resistor required - example
The maximum voltage across an LED is
2 V. The current through it must not
exceed 10 mA. The LED is connected to a
9 V supply. Calculate the value of the
resistor R, connected in series with the
LED.

62. VS = VLED + VR Since LED and resistor in series, what can
we say about the voltage?
VS = VLED + VR
and the current?
the current through each component is the
same (10 mA = A)

64. 7-Segment Displays
LEDs are commonly used in a 7-segment
display.

65. a f b g e c d

66. a f b g e c d

67. Tasks
Numerical Questions 74 – 79
Numerical Questions

68. What have I learned today?

69. Describe where output devices might be used? Can you?
Name some input devices?
State the energy changes in output devices?
State the energy changes in input devices?
Describe applications of input devices?

70. By the end of this lesson you will be able to:
Key words: NPN transistor, MOSFET transistor
By the end of this lesson you will be able to:
Draw and identify the circuit symbol for an
channel enhancement MOSFET.
Draw and identify the circuit symbol for an NPN
transistor.
State that a transistor can be used as a switch
which is ON or OFF.
Explain the operation of a simple transistor
switching circuit.

71. NPN Transistors NPN transistor
The transistor is made from p- and n- type semiconductor materials sandwiched together – n-type, p-type and n-type.
Current arises from the movement of electrons and vacancies called holes.
It is also possible to make a pnp transistor.
Collector
base
Emitter
NPN transistor

72. Digital or analogue? Transistors
base
Collector
The transistor can be used as an electronic switch with no moving parts.
It is either conducting or non conducting i.e. on or off.
Emitter
NPN transistor
Digital or analogue?

73. Transistors The transistor is a digital process device.
base
Collector
The transistor is a digital process device.
Emitter
NPN transistor
When the switch is ON, current flows from the emitter to the collector.

74. How do we turn the switch on?
base
Collector
Whether the switch is on or off depends on the voltage across the base and emitter.
Emitter
NPN transistor
When the base-emitter voltage is less than 0.7 V then no current can flow and the switch is off.

75. The transistor is a voltage controlled switch.
When the base-emitter voltage reaches 0.7 V the switch is on and current flows from the emitter to the collector.
base
Collector
Emitter
NPN transistor
The transistor is a voltage controlled switch.

76. Metal Oxide Semiconductor Field Effect Transistor (MOSFET)
gate
source
drain
The transistor is also made from p- and n- type semiconductor materials.
We will use only one type of MOSFET.

77. Digital or analogue? MOSFET
The transistor can be used as an electronic switch with no moving parts.
It is either conducting or non conducting i.e. on or off.
MOSFET
gate
source
drain
Digital or analogue?

78. MOSFET The MOSFET is a digital process device.
gate
source
drain
The MOSFET is a digital process device.
When the switch is ON, current flows from the source to the drain.

79. How do we turn the switch on?
gate
source
drain
Whether the switch is on or off depends on the voltage across the gate.
When the voltage applied to the gate is less than 1.8 V then no current can flow and the switch is off.

80. What are the advantages of a transistor as a switch?
Fast
Cheap
Reliable
No mechanical parts – don’t wear out
The drawback is that the transitor can be
affected by temperature.

81. Light Controlled Circuits
This diagram shows a complete electronic circuit.
What is the input?
The process device?
The output?

82. Light Controlled Circuits
Input – a voltage divider circuit.
The voltage across the resistor provides the input to the transistor.

83. Light Controlled Circuits
The transistor is the process device.

84. Light Controlled Circuits
The LED is the output device.

85. How it works in the dark:
As light falls, the resistance of the LDR will
increase
therefore the voltage across the LDR will
The input voltage to the transistor therefore
Remember LURD - light up resistance down, so as light goes down resistance goes up

86. How it works in the dark:
As light falls, the resistance of the LDR will
increase
therefore the voltage across the LDR will
The input voltage to the transistor therefore
Remember the greater the resistance, the greater the share of the voltage. The LDR gets a greater share leaving less across the resistor.

87. How it works in the dark:
As light falls, the resistance of the LDR will
increase
therefore the voltage across the LDR will
The input voltage to the transistor therefore
decrease
Remember the voltage across the resistor provides the input to the transistor.

88. 0.7 V switches OFF switches off The transistor is acting as a switch.
When the voltage is below
0.7 V
the transistor
switches OFF
and the LED
switches off
At 0.7 V and above the npn transistor is ON. Below 0.7V the npn transistor is OFF.
The transistor is acting as a switch.
Remember 0.7 V across the base-emitter is the switching voltage for the npn transistor

89. decrease increases Remember light up resistance down.
How it works as light level increases:
As light increases, the resistance of the LDR will
decrease
therefore the voltage across the LDR will
The input voltage to the transistor therefore
increases
Remember light up resistance down.
Remember the smaller the resistance, the smaller the share of the voltage. The LDR gets a smaller share leaving more across the resistor.
Remember the voltage across the resistor provides the input to the transistor.

90. 0.7 V switches ON The transistor is acting as a switch.
When the voltage is above
0.7 V
the transistor
switches ON
and the LED
At 0.7 V and above the npn transistor is ON. Below 0.7V the npn transistor is OFF.
Remember 0.7 V across the base-emitter is the switching voltage for the npn transistor
The transistor is acting as a switch.

91. This circuit switches ON as light levels increase.
How should the components be positioned to give a circuit which switches on as light levels decrease?

92. Another Light Controlled Circuit
Change positions of LDR and Resistor
- light level decreases
- LDR resistance ………….
- voltage across LDR …………….
- transistor switch ……………
- the LED is now …………..
increases
increases ON ON

93. Another Light Controlled Circuit
Explain which circuit would be suitable for use in automatic street lights:
The second circuit in which the LED switches on as light decreases. As darkness falls, this could be used to switch on street lights automatically.

94. Making use of transistors
Input – a voltage divider circuit.
This diagram shows a complete electronic circuit.
The voltage across the thermistor provides the input to the transistor.
The transistor is the process device. V
The LED is the output device.

95. V
How it works –
As the temperature of the thermistor decreases the resistance of the thermistor will
increase
therefore the voltage across the thermistor
increases
The input voltage to the transistor therefore
Remember temperature up resistance down, so as temperature goes down resistance goes up
Remember the greater the resistance, the greater the share of the voltage
Remember the voltage across the thermistor provides the input to the transistor.

96. 0.7 V switches ON lights At 0.7 V and above the npn transistor is ON
When this voltage reaches
0.7 V
the transistor
switches ON
and the LED
lights
At 0.7 V and above the npn transistor is ON
Remember 0.7 V across the base-emitter is the switching voltage for the npn transistor
The transistor is acting as a switch.

97. This circuit acts as a temperature controlled circuit.
It switches on when the temperature is LOW. V

98. How will this circuit behave?
This will act as a temperature controlled circuit which will switch on when temperature rises.

99. Suggest a possible use for this alternative version of the temperature-controlled circuit
This type of circuit might be used in a fridge – to warn when the temperature rises.

100. Another temperature controlled circuit
relay switch
Describe the operation of this circuit.
mains 230 V
Why is it necessary to use a relay switch to operate the heater?
Heating
element
thermistor

101. What have I learned today?

102. By the end of this lesson you will be able to:
Key words: amplifier, gain
By the end of this lesson you will be able to:
Identify, from a list, devices in which amplifiers
play an important part
State that the output signal of an audio amplifier
has the same frequency as, but a larger amplitude
than, the input signal.
Carry out calculations involving input voltage,
output voltage, and voltage gain of an amplifier.

103. What is an amplifier?
An analogue process device. It is used
to make electrical signals bigger.
Amplifier – Physics Animations – Sound –
Amplifying Sound

104. Amplifier Input and Output
Input signal
Output signal
What effect does the amplifier have on the frequency of the signal?
What effect does the amplifier have on the amplitude of the signal?

105. Voltage Gain The amount of amplification of a
particular amplifier is described by its
gain.
What is meant by an amplifier with a gain
of 500?
The output signal is 500 x the amplitude
of the input signal.

106. Voltage Gain If an amplifier has a gain of 500, what
can you say about the frequency of the
input signal and the output signal?

107. Voltage Gain Units? To find the voltage gain of an amplifier we use
output voltage
input voltage Vo
Units? Vi

108. Voltage Gain: Example Units? = 15 Vo Vi 1.5 0.1
The input voltage is 0.1 V and the output is 1.5 V. What
is the amplifier’s gain?
gain =
= 15 Vo Vi
1.5
0.1
Units?

109. Power Gain of Amplifiers
You can also consider the power gain of an
amplifier.
Power gain =
output power
input power
Units?

110. Equations for Power Power can be calculated using equations
which you have come across before.

111. Power Gain: Example A girl connects a set of headphones of
resistance 16 Ω to her MP3 player. The
amplifier in the player produces 0.04 W of
power.
What is the voltage applied to the headphones?
Calculate the input power to the amplifier when
power gain is 20.

112. Solution

113. Solution