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We know that TV can be turned on with infrared light and we know that our body emits infrared to. Does the frequency of our emitted infrared corresponds to the frequency of the device that turns on the TV ?

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TV remotes operate in the near infra-red. For example the TSAL5400 is typical of the IR LEDs used in TV remotes and it uses a wavelength of 940 nm.

The peak wavelength of black body radiation is conveniently given by Wien's displacement law:

$$ \lambda = \frac{b}{T} $$

where $b$ is a constant that is about $2900\,\mu$m K. Using this the peak wavelength of the IR emitted by a human body (at about $37$ºC) is about $9350$ nm, which is a factor of ten too large to interfere with the TV remote.

The spectrum of the EM emitted by a human body does extend up to much shorter wavelengths, but the intensity falls rapidly with decreasing wavelength and will be negligible at TV remote wavelengths. In any case the TV remote does not simply shine an IR beam. It modulates the IR at some few tens of kHz and the receiver on the TV filters out any IR light not modulated in this way. Even if we heated you to the point where you were emitting a lot of near infrared (a few hundred degrees C should do it :-) you still wouldn't interfere with the TV remote.

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  • $\begingroup$ Thanks ! And if we setup a receptor that turns on the TV if he receives 9350 nm wavelength, would it works if we go near it ? Do our body emits with enough "power" or is the "power" of every wavelength emitted the same ? (I mean by "power" the initial condition that can "push" far enough the wave) Because if we put a laser at the same side and mesure the distance that each wave travels to (our body and the laser), the infrared laser will go to infinity while our body will emit in a radius or 20m (or anything < infinty) or am I totally wrong ? $\endgroup$ – Romain B. Jun 21 '17 at 10:17
  • $\begingroup$ @Haatox: Humans emit about the same total power as a filament light bulb i.e. some tens of watts, which is actually quite a lot. Get lots of humans together and they make quite good space heaters! It wouldn't be hard to make a receiver sensitive enough to detect the heat from a human body. $\endgroup$ – John Rennie Jun 21 '17 at 10:30
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    $\begingroup$ So you're telling me that it's as easy as modulating my temperature at a few kHz (and amplifying the intensity of the near-infrared emitted at the necessary frequency)? I'm surprised we don't see more people turning themselves into remotes. $\endgroup$ – JMac Jun 21 '17 at 11:24
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    $\begingroup$ Note that instead of heating yourself to these high temperatures, which is of course unrealistic, one could also run towards the TV. The Doppler shift will allow you to change channels when your velocity is ~0.98$c$. $\endgroup$ – Crimson Jun 21 '17 at 12:03
  • $\begingroup$ TV remotes use certain protocols to operate: even if you emit IR of the right wavelength, nothing will happen unless you signal properly (but that's an engineering problem, not a physics one). $\endgroup$ – NickD Jun 21 '17 at 13:33

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