Most electronic devices are housed in cases designed to trap these electromagnetic waves they are made of metal or have a coating that conducts. The only way to prevent EMI is to keep spurious radio waves under wraps. There is no way to stop electrical devices from generating radio waves. The resulting audio output then would reflect what your computer is doing at that moment but would sound to a person like random squeaks and squawks. In addition to its other components, a cell phone has an audio amplifier that drives its speaker, and the radio waves emitted by the computer may induce currents in the wiring of the amplifier itself.
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Thus, it responds to the resulting cascade of communications failures by creating a series of audible alerts.Īnother explanation involves a deeper connection between your two devices. Computer noise, however, does not contain the sort of information that your phone's onboard computer is programmed to expect. If the signal coming from your computer is strong enough, your phone could mistake it for a cell phone transmission. One explanation for the phenomenon you describe is that your computer unintentionally emits radio waves in the range of frequencies reserved for cell phone communications, typically around 800 megahertz (MHz). Inductive coupling can also have undesirable consequences, however. The same effect is used to heat pots and pans on inductive cooktops. This is how radio receivers detect the signals transmitted by radio stations. Just as changing electric currents radiate radio waves, radio waves induce electric currents in conducting materials. Computers are particularly "noisy" because they rely on rapidly changing currents to act as clock signals that coordinate their calculations. This is an inevitable by-product of using electricity to do useful things, and it is analogous to the clanking and clattering sounds that mechanical devices make as they work. That's because the rapidly changing electric currents running through these devices naturally radiate electromagnetic waves. Virtually every piece of electrically powered equipment acts as a radio transmitter, whether it is supposed to or not. This sounds like a case of electromagnetic interference (or EMI), which is what happens when radio waves emitted by one device cause undesirable behavior in another. David Grier, chair of the physics department at New York University, dials up an answer to this mystery.
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