Electronics “the science that deals with the control of electrons in an electrical circuit or system”
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 Auseful system can change one thing into another. Put a coin in and you get a can of drink out.
The Black Box In electronics we think about the process as a “black box” We use a block diagram to represent the system.
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.
Microphone converts sound energy into electrical energy Amplifier amplifies the weak electrical signal Loudspeaker converts electrical energy into sound energy
Digital and Analogue Signals • There are two types of signals • used by electronic systems: • analogue and digital.
1 0 A digital signal.. …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 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 • As brighter light • shines on the solar • cell, what happens to • the voltage output? Solar Cell Voltmeter
Light Dependent Resistor • We find that increasing light intensity causes an LDR’s resistance to decrease. • Light • Up • Resistance • Down LURD
Thermistor • We find that heating a thermistor causes its resistance to decrease. • Temperature Up Resistance Down
Ohm’s Law V R I
Review • Ohm’s Law calculations involving LDRs and • Thermistors. • Input devices questions.
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.
YES! It doesn’t matter where the resistor is!