Wikipedia:Reference desk/Archives/Science/2024 January 15

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January 15

Human body 5G emission

Using black body radiation, what is the power of what the human body emits in 5G frequencies, compared to a phone? Also, a 100W incandescent lightbulb? Zarnivop (talk) 10:04, 15 January 2024 (UTC)

This sounds potentially like a homework question.

The solution method is to integrate Planck's law over all space, but just for the frequency range of interest. You'll need to specify a surface temperature for a human being and the lightbulb, although the latter is easy to calculate from the power, given the Stefan-Boltzmann law. PianoDan (talk) 15:29, 15 January 2024 (UTC)

I am a bit old for homework. My children are, too. The surface temperature probably is ok with 34 Celsius. I have no idea about the lightbulb. Zarnivop (talk) 17:43, 15 January 2024 (UTC)!

It is much simpler to use Rayleigh–Jeans law for such low frequencies. So, we have for power $P$:

$P={\frac {2\pi k_{B}TS}{3c^{2}}}(\nu _{2}^{3}-\nu _{1}^{3})$

where $S$ is surface area of a human body (or bulb filament), $\nu _{2}$ and $\nu _{1}$ are upper and lower frequencies of the 5G band, $T\approx 300$ K (or 2500 K) and other parameter explained in the article. Ruslik_Zero 21:03, 15 January 2024 (UTC)

so 2×pi×1.38exp(−23)×(273+34)×1.9÷(3×(3 exp(8)^2))×(71 exp(6)-24.25 exp(6))

I got 8.76. 8.76 what?Zarnivop (talk) 01:27, 16 January 2024 (UTC)

Well everything would have to be in SI base units, power in watts but 8.76 watts from a human seems too big. Frequency would have to be in seconds^-1 AKA inverse seconds AKA hertz but 24.25 million hertz and 24.25^6 hertz both seem too low. There seems to be a typo in the formula, they both say v2 or nu2, and they're both cubed I think? Sagittarian Milky Way (talk) 02:11, 16 January 2024 (UTC)

My calculator failed me - it had exp(-27) outside the window. But again, 8.76 exp (-27) What? Watts? Is it even true? Sounds very low to me.Zarnivop (talk) 02:19, 16 January 2024 (UTC)

I fixed an error in index (2->1). So the result for human body is (with $k_{B}=1.380649*10^{-23}$ J⋅K⁻¹, S=1.9 m², $\nu _{1}=10^{9}$ Hz and $\nu _{2}=3*10^{10}$ Hz): P=4.9×10⁻⁶ W. Ruslik_Zero 10:35, 16 January 2024 (UTC)

The nice thing about a consistent system of units of measurement is that you never have to worry about units. Put in all the inputs, including constants, in the base units of the same, consistent system and you'll get the output in base units of the same system. Whether that's SI or cgs doesn't matter. In SI, k_B is in joule per kelvin, T in kelvin, S in square metre, c in metre per second, ν in hertz and P in watt. Note that the US customary system isn't consistent, which is why scientists don't use it. PiusImpavidus (talk) 10:53, 18 January 2024 (UTC)

"Vario speed"??

Siemens claims to have a technology, "Vario speed", that speeds up washing machines cycles without hurting the results. Nowhere did I find what it actually do. Zarnivop (talk) 12:09, 15 January 2024 (UTC)

This technology seems widely used across Siemens products [1]. 78.146.96.26 (talk) 12:30, 15 January 2024 (UTC)

Yes, - or at least they all reduce cycle time and were given the same name. But there is no telling what it is.Zarnivop (talk) 12:49, 15 January 2024 (UTC)

Maybe it's a trade secret. Apparently this company invents 21 things every day [2]. You can check applications at [3]. 78.146.96.26 (talk) 14:03, 15 January 2024 (UTC)

according to 825553 , Reply# 18 it is using higher drum speed (650rpm??) during wash. Zarnivop (talk) 17:49, 15 January 2024 (UTC)

I was hoping they used a bit of intelligence looking at what needed to be done. But no as you say it is running faster - and using more energy. NadVolum (talk) 18:52, 15 January 2024 (UTC)

But for shorter time span. Zarnivop (talk) 01:19, 16 January 2024 (UTC)

More energy overall. NadVolum (talk) 10:17, 16 January 2024 (UTC)

I have seen such a setting on a 'Bosch' (apparently a Bosch/Siemens collaboration) dishwasher. It provided a cycle time approximately 60% of the default 'Eco' cycle time. The dishes came out equally clean, but not so dry. -- Verbarson  ^talk_edits 11:42, 16 January 2024 (UTC)

@NadVolum: your conclusion would depend on 'how much shorter' (time), 'how much faster' (drum speed), the marginal energy cost of the increased speed, and whether any other energy costs or payoffs are involved. Given it's not even known what is involved, let alone specific numbers, I see no basis for your blanket statement. DMacks (talk) 17:35, 24 January 2024 (UTC)

According to a report I saw which tested a number of different settings on some different machines. The eco setting does tend to live up to its name. NadVolum (talk) 17:40, 24 January 2024 (UTC)

Don't know if this is what I read but it covers the area Dishwashers: Testing the energy variability related to different uses. NadVolum (talk) 20:05, 24 January 2024 (UTC)