Diodes and LEDs

There are two more components we should discuss: diodes and LEDs.

Diodes

A diode is a component that only allows current to pass in one direction. The arrow in the circuit symbol indicates this direction:

Next to the circuit symbol on the left, we have a real diode. The stripe represents the stripe in the circuit symbol, and the direction where the current goes out of the diode.

If we look at the following circuits, the one on the left will conduct current while the one on the right will not:

However, even when a diode allows current to pass, it drops the voltage. For a typical value, it drops the voltage by 0.7 V. Let's try and apply Ohm's law to the left circuit again. If the diode drops the voltage by 0.7 V, it means we have 4.3 V across the resistor. This will result in:

LEDs

There is a variation of the normal diode, called Light Emitting Diode or LED. It's basically a very small and efficient light bulb. We can find LEDs in everything these days: displays, phones...