6 ms·
20 minutes per week is probably accurate for how much a person keeps a phone right next to their head these days. It’s not for device usage.
by xwdv 5y ago
20 minutes per week is probably accurate for how much a person keeps a phone right next to their head these days. It’s not for device usage.
- SigmundA 5y agoCareful you might have to explain inverse-square law.
- dragontamer 5y agoRadio is emitted in 3-dimensions, right? So its inverse-cube law?
- ncmncm 5y agoNo.
- ajb 5y agoThe dilution factor is the surface of sphere centered at the emitter, not the volume of the sphere. EM radiation is not like gas diffusion.
- dragontamer 5y agoAppreciated. That explanation makes a lot of sense. EDIT: I also know we aren't dealing with "spheres", but... I get the gist. Dipole antenna emits in this weird doughnut shape, but as a 3-dimensional object, we can estimate it to be kinda-sorta like a sphere :-)
- ajb 5y agoCertainly their surface areas are both O(r^2) :-) Actually though, I think a sphere is still in a way the right object. The weird donut is a representation of the amount that is emitted in different directions - I guess it's a contour of equal intensity. But the radiation is still emitted at the speed of light in every direction. So the wavefront at any given time is a sphere (until it is defracted or reflected). (Edited to add) unless you're thinking of a really big dipole, so you can't treat it as a point source? Or close to it.
- dragontamer 5y agoHmmm. > But the radiation is still emitted at the speed of light in every direction. I think that makes sense. > (Edited to add) unless you're thinking of a really big dipole, so you can't treat it as a point source? Honestly, didn't think of that issue either. You're right though, some antennas (especially AM antennas) are the size of Godzilla, and its absurd to even think of them as point-sources.
- SigmundA 5y agoNo antenna is a perfect point omni emitter, the weird non spherical shapes like doughnuts is the antennas gain, almost are antennas are somewhat directional, the shape is a plot of the measured radiation around the antenna. You take advantage of the fact that it radiates more to the sides than up and down and orient that so it putting more power to the horizon rather than up into space (for terrestrial transmission). The term gain is just referring to the antennas directionality relative to a perfect spherical omni radiator that doesn't exist.
- SilasX 5y agoPlus, didn't phones in that time period have to emit much higher-power signals to work with the contemporary EM infra?
- ncmncm 5y agoHow much time does your cell phone spend in your shirt pocket? Or, your relatives' shirt pockets?
- dragontamer 5y agoCell phones aren't "emitting" signals while in your pocket. They're largely receiving signals and sleeping. We have many devices that emit 10Watts of EM radiation at us every day: we call them light bulbs or LEDs. Cell phones are only allowed to emit 3W IIRC. It wouldn't surprise me if the screen has more EM than the radio.
- ncmncm 5y agoFalse. Cell phones are emitting signals throughout the day, in bursts. LEDs and light bulbs do not emit modulated microwaves. If the screen emitted substantial RF radiation, the FCC (and related agencies in other countries) would have something to say about it.
- dragontamer 5y agoLight is further up the energy-line of electromagnetic radiation. Least-dangerous -- Radio / Infrared / Visible Light / Ultraviolet / XRays / Gamma Rays -- Most energy/dangerous All light-bulbs, screens, LEDs (etc. etc.) emit visible light. There's a couple of bands in there that might be more dangerous than others (ex: Microwaves specifically resonate with water), but for the most part, Gamma Rays are the most dangerous, and Radiowaves have the least effect on our body.