[Music] hi and welcome back to free science lessons. co.uk by the end of this video you should be able to describe and explain the shape of the current potential difference graph for a diode you should then be able to describe what's meant by a light emitting diode and explain why they're useful in the last two videos we've been looking at the current potential difference graphs for a resistor and for a filament lamp remember that the current through resistor is directly proportional to the potential difference as long as the temperature's constant however the current through a filament lamp is not directly proportional to the potential difference and that's because the filament gets hot so the resistance increases now in this video we're going to look at two other components these are called a diode and a light emitting diode which is also called an LED so here's a symbol for a diode and you need to learn this now the key feature of a diode is that the current through the diode Flows In One Direction only that's because the diode has a very high resistance in the reverse Direction I'm showing you a diode in a circuit here if we look again at the symbol for a diode we can see it contains an arrow and that shows us the direction that the conventional current must flow in so here the current's flowing in the forward Direction and the diode allows it through but in this circuit I've turned around the cell so the current's now flowing in the opposite direction that means that the diode will not allow the current to pass through and again that's because the diode has a very high resistance in the reverse Direction so if we take a look at the current potential difference graph for a diode we can see that no current can flow in the reverse Direction however in the forward Direction the current increases as a potential difference increases so what this means is that diodes are extremely useful for controlling the flow of current in circuits now another component that's extremely useful is a light emitting diode or LED so let's look at this now you'll almost certainly have loads of LEDs in your home we find them in almost every electronic gadget for example in the flash on a camera in LED light bulbs and in LED televisions here's a symbol for an LED you'll notice that it's the same as a symbol for diode but it has arrows coming off now an LED is just like a normal diode it only allows current to flow in the forward Direction however unlike a normal diode an LED gives off light when a current flows through LEDs are an extremely energy efficient source of Light which is why they're so useful and why we find them in so many appliances remember you'll find plenty of questions on diodes and LEDs in my vision workbook and you can get that by clicking on the the link above okay so hopefully now you should be able to describe and explain the shape of the current potential difference graph for a diode you should then be able to describe what's meant by a light emitting diode and explain why they're useful [Music]