For this reason a diode in forward bias in a circuit (the position that allows current to flow) is arranged so that the arrow points away from the positive terminal towards the negative terminal.
Electrons Current
Bulb Switch Fig. 10 A selection of diodes. Forward bias
Fig. 11 An electric circuit showing the direction of flow of electrons and the direction of flow of current.
Reverse bias
+ - 6 v
+ - 6 v
Fig. 12 The diode in the left-hand circuit is in forward bias so the bulb lights up; the diode in the right-hand circuit is in reverse bias so the bulb does not light up.
Fig. 13 The symbol for an LED.
Light emitting diodes (LEDs) Light emitting diodes (LEDs) are diodes that light up when the current is flowing through them. Because LEDs are diodes they have to be connected in forward bias in a circuit to allow current to flow and the LED to light up. If too much current flows through an LED it stops working. For this reason, circuits with LEDs usually contain a resistor to reduce the amount of current. An LED has two ‘legs’. The positive leg is the longer leg and it must connect to the positive
- +
Fig. 14 A light emitting diode.
350
terminal on a battery or power pack for current to flow, and the shorter negative leg must connect to the negative terminal of the battery or power pack. The negative leg can also be identified because the side of the LED closest to it is flattened. Light emitting diodes use a lot less energy than light bulbs. An additional benefit is that they do not get anywhere near as hot as light bulbs do and they can last for many years when used correctly. This means that they have many uses including:
