radio waves

• EM waves are made of oscillating electric magnetic fields
• alternating currents are made up of oscillating charges. as the charges oscillate, they produce oscillating electric and magnetic fields , which are EM waves
• The frequency of the waves produced will be equal to the frequency of the alternating current, you can produce radio waves using an alternating current in an electrical circuit. the object in which electrons oscillate to create the radio waves is called a transmitter
• when transmitted radio waves reach a receiver, the radio waves are absorbed. the energy carried by the waves is transferred to the electrons in the material of the receiver. this energy causes the electrons to oscillate and, if the receiver is part of a complete electrical circuit, it generates an alternating current
• the current has the same frequency as the radio wave that generated it
• radio waves are EM radiation with wavelengths longer than about 10cm
• long radio waves (1-10km) can be transmitted and received from halfway across the earth. because long wavelength diffract around the curved surface of the earth
• long wave radio wavelengths can also diffract around hills and into tunnels!
• short wave radio signals (10m-100m) can like long wave, be received at long distances from the transmitter. That's because they are reflected from the ionosphere (an electrically charged layer in the earths upper atmosphere)
• medium wave signals can also reflect from the ionosphere, depending on atmospheric conditions and time of day
• very short wavelengths , to get reception, you must be in direct sight of the transmitter, the signal doesn't bend or travel