Transcript Higher Unit 1

Electronics
“the science that
deals with the
control of
electrons in an
electrical circuit
or system”
Electronics around us
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.
Electronic Systems
A
useful system can change one thing
into another.
Put a coin in and
you get a can of
drink out.
The iron changes electricity to heat.
The Black Box
In electronics we think about the
process as a “black box”
We use a block diagram to represent
the system.
The Toaster as an electronic
system
Radio Receiver
Electronic Thermometer
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.
Battery operated torch
Microphone
Amplifier
Loudspeaker
converts sound
energy into
electrical
energy
amplifies the
weak electrical
signal
converts
electrical
energy into
sound energy
Digital and Analogue Signals
There are two types of signals
used by electronic systems:
analogue and digital.
A digital signal..
1
0
…can have only 2 values, 1 or 0
An analogue signal...
…can have any value
Analogue Signals
Continuous
range of
values
Digital Signals
Only two
possible values
Maximum (logic
‘1’ or high)
Minimum (logic
‘0’ or low)
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.
Input Devices
An input device converts
some form of energy into an
electrical signal.
The microphone as an input
device
Microphone
What is the energy change which takes place in a microphone?
The microphone converts sound energy into an
electrical signal.
Everyday uses of microphones?
Thermocouple
What is the energy change which takes
place in the thermocouple?
The thermocouple converts heat energy
into an electrical signal.
Thermocouple
The sensitivity of the thermocouple
is 40 µV / °C.
For every degree above room
temperature the voltmeter reading
increases by
0.00004 V
Thermocouple
The hotter the temperature the higher
the reading on the voltmeter.
The colder the temperature the lower the
reading on the voltmeter.
Thermocouple
The largest voltage reached was
mV.
To convert to V we divide by 1000:
Thermocouple
Readingfrom voltmeter in volts

0.00004
Added to room temperature of 23 °C means the
highest temperature is
The Solar Cell
A solar cell converts
light (solar) energy into
an electrical signal.
The Solar Cell
Solar
Cell
Voltmeter
As brighter light
shines on the solar
cell, what happens to
the voltage output?
Light Dependent Resistor
We find that increasing
light intensity causes an
LDR’s resistance to
decrease.
Light
Up
Resistance
Down
Thermistor
We find that heating a
thermistor causes its
resistance to decrease.
Temperature Up Resistance Down
Ohm’s Law
V
I
R
Review
Ohm’s Law calculations involving LDRs and
Thermistors.
Input devices questions.
What have I learned today?
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.
Output Devices
The electric motor converts electrical
energy into
kinetic energy
Output Devices
The relay switch is a magnetically
operated switch.
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.
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
The Light Emitting Diode
(LED)
The LED is an output device which
changes electrical energy into
light
DON’T CONFUSE IT
WITH AN LDR!
LED
A filament lamp and an LED are normally
used for different purposes.
Where might an LED be used?
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.
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.
Will this LED light?
YES!
Will this LED light?
YES!
Will this LED light?
YES!
It doesn’t
matter
where the
resistor
is!
But…will this LED light?
NO!
Will this LED light?
NO!
It doesn’t matter where
the resistor is…
but if the
LED is
“facing
the wrong
way” it
will not
light!
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.
What about…this LED?
Will this LED light?
Oops –
you’ve
blown
it up!
Series Resistor and LEDs
Virtual Int 2 Physics -> Electricity &
Electronics -> Electronic Components ->
Series Resistor for an LED
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.
What about…this LED?
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 = 0.010 A)
Since the LED and resistor are in series, what
can we say about the voltage?
VS = VLED + VR
supply voltage
and the current?
voltage across the resistor
voltage across the LED
the current through each component is the
same (10 mA = 0.010 A)
VS  VLED  VR
T o find VR we must takeVLED fromeach side
VR  VS – VLED  5 – 2.3  2.7 V
VR  IR
2.7  0.010x R
2.7
R
 270 
0.01
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.
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 = 0.010 A)
VS  VLED  VR
VR  VS – VLED  9 – 2  7 V
VR  IR
7  0.010x R
7
R
 700 
0.01
7-Segment Displays
LEDs are commonly used in a 7-segment
display.
a
f
e
g
d
b
c
a
f
e
g
d
b
c
Tasks
Numerical Questions 74 – 79
Numerical Questions 80 - 83
What have I learned today?
Describe where
Can you?
output devices
might be used?
Name some input devices?
State the energy
changes in input
devices?
State the energy
changes in
output devices?
Describe applications of input devices?
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.
NPN Transistors
Collector
base
Emitter
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.
Transistors
Collector
base
Emitter
NPN transistor
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.
Digital or analogue?
Transistors
Collector
base
Emitter
The transistor is a
digital process
device.
NPN transistor
When the switch is ON, current flows
from the emitter to the collector.
How do we turn the switch on?
Collector
base
Emitter
NPN transistor
Whether the switch is
on or off depends on
the voltage across
the base and emitter.
When the base-emitter voltage is less
than 0.7 V then no current can flow
and the switch is off.
Collector
base
Emitter
NPN transistor
When the baseemitter voltage
reaches 0.7 V the
switch is on and
current flows from
the emitter to the
collector.
The transistor is a voltage controlled
switch.
Metal Oxide Semiconductor Field
Effect Transistor (MOSFET)
drain
The transistor is
also made from pand n- type
semiconductor
materials.
We will use only
one type of
MOSFET.
gate
source
MOSFET
MOSFET
drain
The transistor can be
used as an electronic
switch with no
moving parts.
gate
source
MOSFET
It is either conducting
or non conducting i.e.
on or off.
Digital or analogue?
MOSFET
drain
The MOSFET is a
digital process
device.
gate
source
MOSFET
When the switch is ON, current flows
from the source to the drain.
How do we turn the switch on?
drain
gate
Whether the switch is
on or off depends on
the voltage across
the gate.
source
When the voltage applied to the gate
is less than 1.8 V then no current can
flow and the switch is off.
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.
Light Controlled Circuits
This diagram
shows a
complete
electronic circuit.
What is the
input?
The process
device?
The output?
Light Controlled Circuits
Input – a voltage
divider circuit.
The voltage across the
resistor provides the
input to the
transistor.
Light Controlled Circuits
The transistor is the
process device.
Light Controlled Circuits
The LED is the output
device.
How it works in the dark:
As light falls, the resistance of the LDR will
increase
therefore the voltage across the LDR will
Remember LURD light up resistance
down, so as light goes
down resistance goes
up
The input voltage to the transistor therefore
How it works in the dark:
As light falls, the resistance of the LDR will
increase
therefore the voltage across the LDR will
increase
Remember the greater
the resistance, the
greater the share of
the voltage. The LDR
gets a greater share
leaving less across the
resistor.
The input voltage to the transistor therefore
How it works in the dark:
As light falls, the resistance of the LDR will
increase
therefore the voltage across the LDR will
increase
Remember the voltage
across the resistor
provides the input to
the transistor.
The input voltage to the transistor therefore
decrease
When the voltage is below
0.7 V
the transistor
switches OFF
and the LED
At 0.7 V and above the npn
transistor is ON. Below
switches off
0.7V the npn transistor is
OFF.
The transistor is
Remember 0.7 V
across the baseacting as a switch.
emitter is the
switching voltage for
the npn transistor
How it works as light level increases:
As light increases, the resistance of the LDR
will
decrease
therefore the voltage across the LDR will
decrease
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.
The input voltage to the transistor therefore
increases
Remember the voltage
across the resistor
provides the input to
the transistor.
When the voltage is above
0.7 V
the transistor
switches ON
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
and the LED
switches ON
The transistor is
acting as a switch.
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?
Another Light Controlled Circuit
Change positions of LDR and
Resistor
- light level decreases
increases
- LDR resistance ………….
increases
- voltage across LDR …………….
ON
- transistor switch ……………
ON
- the LED is now …………..
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.
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.
How it works –
As the temperature of the thermistor
decreases the resistance of the thermistor
will
V
increase
therefore the voltage across the thermistor
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
increases
The input voltage to the transistor therefore
increases
Remember the voltage
across the thermistor
provides the input to the
transistor.
When this voltage reaches
0.7 V
V
the transistor
switches ON
At 0.7 V and above the
npn transistor is ON
Remember 0.7 V
across the baseemitter is the
switching voltage for
the npn transistor
and the LED
lights
The transistor is
acting as a switch.
This circuit acts as a
temperature
controlled circuit.
V
It switches on when
the temperature is
LOW.
How will this circuit
behave?
V
This will act as a temperature controlled
circuit which will switch on when
temperature rises.
V
Suggest a possible use
for this alternative
version of the
temperaturecontrolled circuit
This type of circuit might be used in a fridge
– to warn when the temperature rises.
Another temperature controlled
circuit
relay switch
mains
230 V
thermistor
Heating
element
Describe the
operation of this
circuit.
Why is it
necessary to
use a relay
switch to
operate the
heater?
What have I learned today?
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.
What is an amplifier?
An analogue process device. It is used
to make electrical signals bigger.
Amplifier – Physics Animations – Sound –
Amplifying Sound
Amplifier Input and Output
Amplifier
Input signal
Output signal
What
does
the the
amplifier
have onhave
the amplitude
Whateffect
effect
does
amplifier
on the of
the signal?
frequency of the signal?
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.
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?
Voltage Gain
To find the voltage gain of an amplifier
we use
voltage gain =
output voltage
input voltage
gain =
Vo
Vi
Units?
Voltage Gain: Example
The input voltage is 0.1 V and the output is 1.5 V. What
is the amplifier’s gain?
Vo
gain =
Vi
gain =
1.5
0.1
= 15
Units?
Power Gain of Amplifiers
You can also consider the power gain of an
amplifier.
Power gain =
output power
input power
Units?
Equations for Power
Power can be calculated using equations
which you have come across before.
2
V
P
R
P  VI
PI R
2
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.
Solution
2
V
P
R
2
V
0.04 
R
2
0.04R  V
V  0.04x16  0.64
V  0.8V
2
Solution
output
gain 
input
0.04
20 
input
20xinput  0.04
0.04
input 
20
3
input  2 x10 W  20m W