Diode and Semiconductor

What does a diode do?

A diode is very important to electronics and radios and it controls the direction of electrical current.

What is a semiconductor?  

A semiconductor is an electronic component that is between an insulator and a conductor. That is where it gets its name, a semiconductor.

Why is a diode necessary for a crystal radio?  

A diode in a crystal radio is necessary because it changes or converts the radio waves from amplitude modulation (AM) to a direct current (DC), which will direct the wave to your earpiece.