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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 Reading from 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 To find VR we must take VLED from each side VR VS – VLED 5 – 2.3 2.7 V VR IR 2.7 0.010 x 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 0.010 x 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 PI 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 0.04 R V V 0.04 x16 0.64 2 V 0.8V Solution output gain input 0.04 20 input 20 xinput 0.04 0.04 input 20 3 input 2 x10 W 20mW