ELECTRONICS Learning Objective To know how the thermisistor works Can describe uses for the Light dependent resistor (LDR) Can explain the applications of the diode

ELECTRONICS Components Electronic devices are composed of ‘components’ or parts We will look at three components in particular: The Diode The Light Emitting Diode (LED) The Light Dependent Resistor (LDR)

Summary of components we may already be familiar with: ELECTRONICS Components Summary of components we may already be familiar with: Switch A switch is a device for completing or breaking circuits. When a switch is closed current will flow When a switch is opened the circuit is broken and no current can flow Switch symbol

ELECTRONICS Components Resistor VariableResistor symbol A resistor is a component that is used to control the amount of current flowing in a circuit. A ‘variable’ resistor is a component whose resistance can be changed while connected in a circuit to allow different amounts of current to flow ( e.g. a dimmer switch ) VariableResistor symbol Resistor symbol

Diode Now Lets look at some new components The diode Allows electric current to flow in one direction only

Diode The diode symbol Direction of Current This end represents the ‘positive’ end of the diode Silver bar at end of diode represents the ‘negative’ end of the diode This end represents the ‘negative’ end of the diode The diode symbol Direction of Current

The diode (Forward bias) The diode (Reverse bias) When diode allows current to conduct it is said to be ‘forward bias’ The diode (Reverse bias) When diode does not allow current to conduct it is said to be ‘reverse bias’

Diode The diode is a non-ohmic conductor. It allows the current to flow in one direction only. Doesn’t allow the current to flow (has infinite resistance in the reverse direction) Allows the current to flow in the forward direction

Diode Current (A) Voltage (V) diode Plotting a current-voltage graph for a diode produces this shape line Current (A) Very steep resistance is very small once certain voltage is reached Voltage (V)

Applications of the Diode Used in Power Supply Units to change from alternating current (a.c) to direct current (d.c) (diodes used this way are referred to as a ‘rectifier’) Used in circuits to make sure current flows in one direction only (example: bedside buttons in hospitals that connect to the nurses station activating a buzzer)

Diode

Diode

The Light-Emitting Diode (LED) Diodes that give out light when current flows through them are called Light-Emitting Diodes (LED). The LED will only allow current flow through it when it is ‘forward biased’ When forward biased the LED emits light

The Light-Emitting Diode (LED) LED uses very small current when emitting light To prevent damage to the LED, a ‘resistor’ will always be connected in series with the LED LED Symbol LEDs

LED For ‘forward bias’ connection the long lead of the LED (Anode) is connected toward the +ve side of battery. The short lead (Cathode) connected toward the –ve end of battery. Connections are other way around for ‘reverse bias’ operation

Applications of the LED Used in displays such as calculators, alarm clocks Used in TVs to show that there is power to the unit LED lamps ( Torches, Bicycle and Car lights)

The Light-Dependent Resistor (LDR) A resistor whose value of resistance can change as the intensity of the light falling on it changes If bright light falls on LDR the resistance is low ( larger current can flow) If dim light falls on LDR the resistance is high ( smaller current will flow)

The Light-Dependent Resistor (LDR) The LDR LDR Symbol

Applications of the LDR Streetlights. When darkness falls, resistance of LDR increases and used to control switching on of light Cameras. Uses amount of light entering camera to control camera settings

Thermistor A resistor whose value of resistance can change as the temperature changes If it is warm the thermistors resistance is low ( larger current can flow) If it is cold the thermistors resistance is high ( smaller current will flow)

Thermistor

Applications of the thermistor Bath thermometers (Baby thing, ask Mr Gamble!) Anything that senses temperature

Thermistor

Transducers Is a funny word… Light is the input transducer for a LDR

ELECTRONICS Battery Power Supply Unit Component Symbol Thermistor Battery Power Supply Unit Identify the component from the symbols shown Switch Resistor Diode LED LDR

Key Points ( Fill in the Gaps ) ELECTRONICS Key Points ( Fill in the Gaps ) A _______ allows current to flow in only one direction The LED is a diode that emits ________ when in forward bias A _________ is placed in series with an LED to limit the current An LDR is a resistor whose value of resistance changes as the intensity of the __________ falling on it changes diode light resistor light

Key words Electronics Component Diode Forward bias Reverse bias Anode Cathode Light Emitting Diode (LED) Light Dependent Resistor (LDR) Thermistor Transducer

ELECTRONICS The End