The Physics Question Bank

A radio works by sending information using radio waves. Radio waves are part of the electromagnetic spectrum. This means they are the same type of wave as microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.

Radio waves are useful because they can travel very long distances. They do not need particles to travel through, so they can move through air and even through space. Like all electromagnetic waves, radio waves travel at about 300,000,000 m/s in a vacuum.

The first step happens at the radio station. When someone speaks or music is played, the sound is changed into an electrical signal. A microphone can do this. The electrical signal changes in the same pattern as the sound.

This electrical signal is then added to a radio wave. The radio wave is called a carrier wave because it carries the information. The information is not sent as a normal sound wave. Instead, it is sent as changes in the radio wave.

This process is called modulation. It means changing the carrier wave so that it contains the information from the sound.

The transmitter sends the radio wave out using an aerial. The radio waves spread out from the transmitter and travel through the air.

Your radio also has an aerial. When the radio waves reach the aerial, they make electrons in the metal move backwards and forwards. This creates a tiny alternating current in the aerial.

Your radio then tunes into one frequency. Frequency means the number of waves passing a point each second. It is measured in hertz, Hz. Different radio stations use different frequencies, so tuning the radio means choosing the frequency of the station you want.

The radio then separates the sound information from the carrier wave. This is called demodulation.

Finally, the electrical signal is sent to a loudspeaker. The loudspeaker changes the electrical signal back into sound. The speaker cone vibrates, which makes air particles vibrate. These vibrations travel to your ear as sound waves.

So the whole process is:

sound → electrical signal → radio wave → electrical signal → sound

This is why you can hear someone speaking from many miles away. Their voice is not travelling all the way to you as a sound wave. Instead, information about their voice is carried by radio waves and then turned back into sound by your radio.

The key GCSE physics ideas are:

Radio waves are electromagnetic waves.

They can travel through air and space.

Sound is changed into an electrical signal.

The electrical signal is carried by a radio wave.

The aerial receives the radio wave.

The loudspeaker changes the electrical signal back into sound.

A simple exam-style answer could be:

A radio station changes sound into an electrical signal. This signal is used to modulate a radio wave, which is transmitted by an aerial. The radio receives the wave, selects the correct frequency, and changes the electrical signal back into sound using a loudspeaker.