Naked Science Forum
Non Life Sciences => Technology => Topic started by: toddnaomi7 on 21/11/2010 20:51:05
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Does a cell phone or a candle give off more electromagnetic radiation?
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It depends; is the candle lit?
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[:)] Wise guy! Let me clearify ...
Cell phone: a typical modern cell phone that is powered on and within a mile of a cell tower.
Candle: a common unscented taper candle which has been lit and is located in a room at STP with 20% oxygen in the air.
I could probably figure out the the wattage with a little experimentation (which I would rather not do), but I would still be stuck since I don't know what percentage of that energy is electromagnetic radiation.
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I guess all the visible light and infrared heat from the candle is electromagnetic radiation. So that's quite a bit of energy. Also, the candle's duty cycle is 100% whereas the phone probably has a very small duty cycle as it only transmits for short intervals (I'm assuming the phone is not actually making a call.)
Soooooo, I would think the candle is producing a lot more RF energy.
Another clue might lie in the fact that you can put an active cell phone in your pocket but you can't put an active candle in your pocket (for very long). Admittedly, the frequencies are very different, so this may not be a valid proof.
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I would think the candle is producing a lot more RF energy.
Do flames produce appreciable amounts of RF ?,
I've never heard someone say "there's a lot of interference on my mobile phone coz I'm too close to the fireplace".
Electrical sparks (http://en.wikipedia.org/wiki/Spark-gap_transmitter) yes, but I haven't heard of flames causing EMI (http://en.wikipedia.org/wiki/Electromagnetic_interference).
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Do flames produce appreciable amounts of RF ?,
Visible light, infrared radiation and radio waves are all forms of electromagnetic radiation. I probably should not have described the candle as a source of RF, because the frequencies are much higher than typical RF.
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Ok here's a geeky answer.
A candle is a roughly 2000K black body radiator. That means (assuming I did the calculation right), that it gives off only about 0.5% of its total power in the visible range, since it's relatively cool.
The standard for light output used to be based on candles, and so there's still a unit around called a "candela," which is based on the light output of a candle. Working from this value, the visible light output by a standard candle is roughly 0.018 Watts.
If the other 99.5% of the energy is output as radiation other than visible light, that means that the total output of the candle is somewhere around 3.7 Watts.
There's a lot of assumptions here, but this number is probably in the right ballpark of a candle's power output.
A cell phone can operate at a max power of 2 Watts, according to Wikipedia. This is similar to the power output of a candle. But a cell phone doesn't operate at this power all the time, while a candle does. The candle probably emits more power.
So in the end, I did a lot of math only to find out Geezer was probably right. I hate it when that happens!
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It's true that a candle is relatively cool, but it's damned hard to make a 'phone call with one.
The "standard candle" used to burn 120 grains of wax (sperm wax to be precise) per hour.
The bottle of cooking oil in my kitchen tells me that burning fats give about 37 KJ/g .
A rate of 120 grains per hour is about 7.78 grams per hour or about 2.16 mg/ sec
That gives a power output of about 80 watts (which seems a lot to me, can someone check my maths etc?).
If about 5% of that is radiated away ( rather than convected or conducted) then the numbers tally.
The candle radiates more than the RF from the 'phone and I don't think the 'phone will be hot enough to emit enough black body radiation to catch up.
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Can 4 candles pop corn like 4 cell phones can at the same distance.
What magnatude of radiation energy is needed or is it in the concentrated focus of radiation
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Can 4 candles pop corn like 4 cell phones can at the same distance.
What magnatude of radiation energy is needed or is it in the concentrated focus of radiation
That video is faked ... http://edition.cnn.com/video/#/video/tech/2008/07/09/carroll.cellphone.popcorn.cnn
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Can 4 candles pop corn like 4 cell phones can at the same distance.
What magnatude of radiation energy is needed or is it in the concentrated focus of radiation
That video is faked ... http://edition.cnn.com/video/#/video/tech/2008/07/09/carroll.cellphone.popcorn.cnn
HAHA I've been duped again, when is this ever going to stop.
Thanks
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[;D] Thanks for all the feedback. The info was very helpful -- especially the "geeky answers" of JP and Bored Chemist.