An electromagnetic wave itself does not carry sound directly. Sound is a mechanical wave that requires a medium, such as air or water, to propagate. However, electromagnetic waves can carry information that can be used to reproduce sound and images.
When it comes to transmitting sound and images using electromagnetic waves, different techniques are employed. Let's consider two common examples: radio waves for sound and television signals for images.
- Radio Waves for Sound: When transmitting sound over radio waves, the sound is typically converted into an electrical signal. This signal represents variations in amplitude, or the strength, of the wave. The electrical signal is then modulated onto a carrier wave, which is an electromagnetic wave of a specific frequency. The carrier wave acts as a "transport" for the modulated sound signal.
In amplitude modulation (AM), variations in the amplitude of the carrier wave are used to encode the sound signal. The audio signal is superimposed onto the carrier wave, causing the amplitude of the carrier wave to vary in response to the sound signal. The receiver can then extract the audio signal by demodulating the received carrier wave, recovering the original sound.
- Television Signals for Images: Television signals involve transmitting both sound and images simultaneously. In this case, the image information is carried separately from the sound. Television signals use a combination of amplitude modulation and frequency modulation.
The video signal, which represents the image information, is typically transmitted using amplitude modulation (AM). The intensity of the video signal varies the amplitude of the carrier wave, encoding the brightness or color information of the image.
The audio signal, representing the sound, is transmitted using frequency modulation (FM). Variations in the audio signal cause the frequency of the carrier wave to change, resulting in changes in pitch or frequency of the sound.
At the receiving end, the television receiver demodulates the carrier waves, separating the video signal from the audio signal. The video signal is used to recreate the image on the screen, while the audio signal is used to reproduce the sound.
It's important to note that in modern digital systems, such as digital television (DTV) and digital radio, the transmission and reception processes are more complex, involving encoding and decoding of digital signals. However, the basic principles of modulating and demodulating the carrier wave to carry separate audio and video information still apply.
In summary, electromagnetic waves are used as carriers for transmitting sound and image information by modulating their amplitude and frequency. The amplitude modulation (AM) technique is often used for carrying sound, while the amplitude modulation (AM) and frequency modulation (FM) techniques are employed for carrying image (video) signals.