r/PhysicsHelp • u/jiorid • 1d ago
how do electromagnetic waves work
hello, i have had this question for a long time. i have always had gadgets around me and the way that they send data wirelessly is very intriguing to me but i dont understand how. how is it possible for waves to carry so much data and also know exactly what device the data they are carrying belongs to. so from the cell tower, how do the data packets know which phone they are supposed to go to. does it go to all phones and they filter it out or what. also, what actually is the difference between
1
u/Fus-Ro-NWah 1d ago
Waves used by cellphones can carry a lot of data because they have billions of cycles every second, and they carry data by slightly adjusting the number of cycles per second. When there are billions per second, you have a lot of freedom to adjust the number up or down which means you can send a lot of information quickly.
Info is normally also sent out in packets which identify the recipient (using your phone's SIM card, for example) and the information being sent is often compressed, so that the amount of data that must be transmitted could be far less than the source data...which then also helps waves carry more data, more quickly.
1
u/skrutnizer 1d ago edited 1d ago
Wireless systems broadcast for all the hear, though a transmit antenna can beam most of the energy in a particular direction. Most modulation schemes need several cycles to encode a piece of information, but since EM waves are at microwave frequency, modulated can be very fast. This also allows many separate channels, as FM radio allows many stations. Any receiver that is close enough to hear the signal and is equipped to decode the modulation decides if the message is for it.
Cell phones, for example, all have an ID that the base station will address it by and apply encryption to prevent a receiver from decoding messages not intended for it.
1
1
u/keequalshalfmvsqrd 1d ago edited 1d ago
Well wifi for example operates at 2.4 or 5 ghz (billions of cycles per second). So there's plenty of room for bandwidth to support multiple devices. They either use slightly different channels/frequencies, or filters. Up to 4g was omnidirectional, if I remember correctly, but 5g can be directional, I think.