CHAPTER 31 – ELECTRONIC CIRCUITS LEDs


An LED (light-emitting diode) is a type of diode that lights up when a current flows through it. As is the case with all diodes, current can only flow through an LED in one direction.


An LED uses less current than a bulb to work.


To connect an LED in forward bias, the negative terminal of the LED (the shorter of the two legs) is connected to the negative terminal of the battery.


Eureka


LEDs can produce any colour of light. They also generate very little heat, reducing the risk of fire. Together, these features make them suitable for decorations, such as Christmas tree lights.


)Fig. 31.14 Christmas tree lights ? TEST TUBE


3. What does the abbreviation LED stand for? 4. In what way must an LED be connected for it to emit light? 5. LEDs are now replacing most other sources of light in the home. Explain why you think this might be.


EXPERIMENTAL INVESTIGATION 31.2


What effect does an LED have on a circuit when connected in forward bias and reverse bias?


Equipment Wires Switch


Method


1. Connect the switch and resistor to the battery, as shown in Fig. 31.16.


2. Connect two parallel paths from the resistor back to the battery.


3. Place one LED in forward bias (shorter leg of the LED to the negative terminal of the battery).


5. Close the switch and record your observations.


)Fig. 31.16 To investigate the effect on a circuit of an LED connected in forward bias and reverse bias


LEDs j Go to page 98 of your Experimental Investigations Log to write up this investigation.


SAFETY • Be careful of sharp ends on the wires.


• Do not set the power supply too high (check with your teacher before turning circuit on).


Switch


4. Place one LED in reverse bias (shorter leg of the LED to the positive terminal of the battery).


Resistor Power supply


Resistor Battery


2 LEDs Crocodile clips (to connect wires to components if necessary)


:Fig. 31.15 An LED – +


Elements of Science 309


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