Electronics

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Electronics
the science that deals with the control of
electrons in an electrical circuit or system
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Electronics around us
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• 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 VIR for the
• thermistor and LDR.

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Electronic Systems
A useful system can change one thing into
another.
Put a coin in and you get a can of drink out.
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• The iron changes electricity to heat.

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The Black Box
In electronics we think about the process as a
black box We use a block diagram to
represent the system.
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The Toaster as an electronic system
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Radio Receiver
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Electronic Thermometer
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• 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.

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Battery operated torch
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Microphone converts sound energy into
electrical energy
Amplifier amplifies the weak electrical signal
Loudspeaker converts electrical energy into
sound energy
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Digital and Analogue Signals

• There are two types of signals
• used by electronic systems
• analogue and digital.

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A digital signal..
can have only 2 values, 1 or 0
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An analogue signal...
can have any value
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Analogue Signals
Continuous range of values
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Digital Signals
Only two possible values Maximum (logic 1 or
high) Minimum (logic 0 or low)
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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.

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Input Devices

• An input device converts
• some form of energy into an
• electrical signal.

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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?
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Thermocouple

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

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Thermocouple

• The sensitivity of the thermocouple
• is 40 µV / C.
• For every degree above room
• temperature the voltmeter reading
• increases by
• 0.00004 V

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Thermocouple

• The hotter the temperature the higher
• the reading on the voltmeter.
• The colder the temperature the lower the
• reading on the voltmeter.

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Thermocouple

• The largest voltage reached was
• mV.
• To convert to V we divide by 1000

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Thermocouple
Added to room temperature of 23 C means the
highest temperature is
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The Solar Cell

• A solar cell converts
• light (solar) energy into
• an electrical signal.

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The Solar Cell
Solar Cell
Voltmeter

• As brighter light
• shines on the solar
• cell, what happens to
• the voltage output?

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Light Dependent Resistor
We find that increasing light intensity causes
an LDRs resistance to decrease.

• Light
• Up
• Resistance
• Down

LURD
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Thermistor
We find that heating a thermistor causes its
resistance to decrease.

• Temperature Up Resistance Down

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Ohms Law
V
R
I
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Review

• Ohms Law calculations involving LDRs and
• Thermistors.
• Input devices questions.

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What have I learned today?
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• 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.

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Output Devices

• The electric motor converts electrical
• energy into
• kinetic energy

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Output Devices

• The relay switch is a magnetically
• operated switch.

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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.

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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 -gt Electricity and Electronics -gt
Electronic Components -gt Output Devices
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The Light Emitting Diode (LED)

• The LED is an output device which
• changes electrical energy into
• light

DONT CONFUSE IT WITH AN LDR!
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LED
A filament lamp and an LED are normally used for
different purposes. Where might an LED be used?
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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.
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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.
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Will this LED light?
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YES!
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Will this LED light?
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YES!
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Will this LED light?
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YES!
It doesnt matter where the resistor is!
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Butwill this LED light?
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NO!
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Will this LED light?
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NO!
It doesnt matter where the resistor is but if
the LED is facing the wrong way it will not
light!
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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.

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What aboutthis LED?
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Will this LED light?
Oops youve blown it up!
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Series Resistor and LEDs

• Virtual Int 2 Physics -gt Electricity
• Electronics -gt Electronic Components -gt
• Series Resistor for an LED

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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.

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What aboutthis LED?
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• 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)

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• 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)

supply voltage
voltage across the resistor
voltage across the LED
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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.

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• 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)

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7-Segment Displays

• LEDs are commonly used in a 7-segment
• display.

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a
f
b
g
e
c
d
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a
f
b
g
e
c
d
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Tasks

• Numerical Questions 74 79
• Numerical Questions 80 - 83

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What have I learned today?
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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?
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• 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.

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NPN Transistors
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
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Transistors
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.
Collector
Emitter
NPN transistor
Digital or analogue?
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Transistors
The transistor is a digital process device.
Collector
Emitter
NPN transistor
When the switch is ON, current flows from the
emitter to the collector.
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How do we turn the switch on?
Whether the switch is on or off depends on the
voltage across the base and emitter.
Collector
Emitter
NPN transistor
When the base-emitter voltage is less than 0.7 V
then no current can flow and the switch is off.
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When the base-emitter voltage reaches 0.7 V the
switch is on and current flows from the emitter
to the collector.
Collector
Emitter
NPN transistor
The transistor is a voltage controlled switch.
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Metal Oxide Semiconductor Field Effect Transistor
(MOSFET)
The transistor is also made from p- and n- type
semiconductor materials. We will use only one
type of MOSFET.
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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.
Digital or analogue?
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MOSFET
The MOSFET is a digital process device.
When the switch is ON, current flows from the
source to the drain.
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How do we turn the switch on?
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.
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What are the advantages of a transistor as a
switch?

• Fast
• Cheap
• Reliable
• No mechanical parts dont wear out
• The drawback is that the transitor can be
• affected by temperature.

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Light Controlled Circuits
This diagram shows a complete electronic
circuit. What is the input? The process
device? The output?
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Light Controlled Circuits
Input a voltage divider circuit.
The voltage across the resistor provides the
input to the transistor.
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Light Controlled Circuits
The transistor is the process device.
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Light Controlled Circuits
The LED is the output device.
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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
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How it works in the dark As light falls, the
resistance of the LDR will increase therefore
the voltage across the LDR will increase 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.
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How it works in the dark As light falls, the
resistance of the LDR will increase therefore
the voltage across the LDR will increase The
input voltage to the transistor
therefore decrease
Remember the voltage across the resistor provides
the input to the transistor.
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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
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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 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.
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When the voltage is above 0.7 V the transistor
switches ON and the LED 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
The transistor is acting as a switch.
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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?
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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
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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.
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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.
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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 increases
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.
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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.
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This circuit acts as a temperature controlled
circuit. It switches on when the temperature is
LOW.
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How will this circuit behave?
V
This will act as a temperature controlled circuit
which will switch on when temperature rises.
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Suggest a possible use for this alternative
version of the temperature-controlled circuit
V
This type of circuit might be used in a fridge
to warn when the temperature rises.
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Another temperature controlled circuit
Describe the operation of this circuit.
relay switch
mains 230 V
Why is it necessary to use a relay switch to
operate the heater?
Heating element
thermistor
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What have I learned today?
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• 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.

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

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

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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?

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Voltage Gain

• To find the voltage gain of an amplifier
• we use
• voltage gain
• gain

output voltage
input voltage
Vo
Units?
Vi
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Voltage Gain Example

• The input voltage is 0.1 V and the output is 1.5
  V. What
• is the amplifiers gain?
• gain
• gain
• 15

Vo
Vi
1.5
0.1
Units?
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Power Gain of Amplifiers

• You can also consider the power gain of an
• amplifier.
• Power gain

output power
input power
Units?
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Equations for Power

• Power can be calculated using equations
• which you have come across before.

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Power Gain Example

• A girl connects a set of headphones of
• resistance 16 ? 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.

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Solution

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Solution