LED circuit loss of weight due to mass of photons

Sure.

No electrons were lost. The potential energy in the charged cap added mass, per MC^2, and extracting the energy reduced that mass. Same thing happens in chemical and nuclear reactions; a system can conserve particles but still loses mass when it delivers energy. A hot brick is heavier than a cold brick, and a flying baseball is heavier than one at rest.

John

Photons are massless. The mass gets converted to energy.

The assembly will weigh about 5 x 10^-14 grams less (about 32 billion proton masses). Sadly, you won't be able to measure this, because evaporation and oxidation of the casing, adsorbtion of air and pollutants on external surfaces, etc. are all many orders of magnitude greater in effect, let alone the practical matter of a parts-per-quadrillion scale to weigh it on.

Tim

-- Deep Friar: a very philosophical monk. Website:

I never considered that. Is the weigth increase due to heating of the brick purely giverned by E=MC2? (ie would adding one Joulse of energy really increas the weight by 1/C^2 Kg?)

I always thought that quantum physics like E=MC2 only take effect in extreme cases (ie fission or fusion). Could you actually measure (on a

No, it happens whenever energy is stored within matter, like chemical energy, even mechanical energy like a wound-up spring. A well-charged photoflash capacitor (100 joules) weighs about a picogram more than the same cap discharged.

Could you actually measure (on a

Yes. I think maybe it has been done for some chemical reactions. The brick thing is likely too small to measure.

John

Tim

gotta give ya points for a good and original question.

The latter. The electric field in a charged capacitor has mass. The capacitor will lose mass as it discharges, though every electron that leaves it from one lead is replaced by an electron going in the other lead.

- Don Klipstein ( snipped-for-privacy@misty.com)

That part is not true. Although photons have no rest mass - but nobody can slow down a photon. Photons have no matter, but energy has mass, and photons have energy.

Any successful decelleration of a photon will reduce its momentum without reducing its velocity. And photons do have momentum with finite velocity.

- Don Klipstein ( snipped-for-privacy@misty.com)

Ok, mass-energy, but not mass /per se/, by which I meant RME. 'Cuz they're never at rest. Chock it up to ambiguous phrasing?

...And no mass. That sometimes fries people -- "but p = mv!". Ah, but at exactly the speed of light, what is mass?

Ain't relativity great? ;-)

Tim

There was a young lady named Bright Whose speed was much greater than light She set out one day In a relative way And arrived the previous night.

Jim

-- "It is the mark of an educated mind to be able to entertain a thought without accepting it." --Aristotle

And the young man named Fisk whose fencing was exceedingly brisk in a tourney one day in a relative way reduced his rapier to a disk.

I will have to try again, getting the limerick right this time:

There was a young man named Fisk, Whose fencing was exceedingly brisk. So fast was his action that the Fitzgerald contraction reduced his rapier to a disk.

- unknown

As others have said - the charge. Also worth noting is that photons have momentum. My keyring torch weighs some 40g, and outputs some 1000J of photons.

This would impart a momentum of some 1000J/C - or 3*10^-6Kgm/s, or the heady speed of 75 microns/second, or over the hour and a half or so of discharge, 20cm or so, ending up at a speed of some 2Km/year.

Whoa, keep a tight grip on that thing!

John

After carefully considering the problem and applying my advanced mathematical skills, I conclude that the interval in question is an hour and a half or so.

John