# Television Sets Weighing More

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 726166.  Tue Jul 06, 2010 8:18 pm This last fact thrown in at the end of the show got me thinking. A television set would actually weigh more (however marginal) when plugged in. Energy has a very minuscule mass but a mass nonetheless. The electrons flowing through the set have a mass that gravity could pull on. So, televisions should weigh ever so slightly more when powered on, especially when you take into account the capacitors not just current.

726176.  Tue Jul 06, 2010 10:47 pm

 Quote: Energy has a very minuscule mass but a mass nonetheless

I may be wrong but I would say that Energy doesn't have a mass - it is equivalent to a mass which isn't the same thing.

 726190.  Wed Jul 07, 2010 1:15 am Cough!

726218.  Wed Jul 07, 2010 4:24 am

 bobwilson wrote: I may be wrong but I would say that Energy doesn't have a mass - it is equivalent to a mass which isn't the same thing.

There's no "may" about it. You're definitely wrong.

Sadly for Posital, the Crookes radiometer does not turn due to the pressure of light. That was a theory that Sir William Crookes originally came up with to explain the effect, but he was later shown to have been incorrect.

A Nichols radiometer is the thing you want to prove that the pure energy of light has momentum and, therefore, mass. Or, if you can measure the position of a rotating asteroid accurately enough, you can observe the Yarkovsky effect.

726250.  Wed Jul 07, 2010 7:26 am

 Posital wrote: Cough!

Seriously, I'd get something for that :)

 726259.  Wed Jul 07, 2010 8:18 am The whole electron adding to the weight theory is attractive but erroneous. The TV has the same number of electrons in it whether it is on or off, it's just that when it's on they are moving.

726319.  Wed Jul 07, 2010 2:16 pm

 dr.bob wrote: Sadly for Posital, the Crookes radiometer does not turn due to the pressure of light.
Well I be jiggered - thanks for putting me right, bob. In my defence - I always thought it was in a vacuum. Ah well.

726398.  Thu Jul 08, 2010 4:10 am

 Efros wrote: The whole electron adding to the weight theory is attractive but erroneous. The TV has the same number of electrons in it whether it is on or off, it's just that when it's on they are moving.

...and therefore have more energy, and therefore weigh more.

E=mc^2, dude! Not erroneous at all.

 726412.  Thu Jul 08, 2010 5:24 am Burglars report that TV sets are more difficult to move when plugged in and switched on.

726429.  Thu Jul 08, 2010 6:51 am

dr.bob wrote:
 Efros wrote: The whole electron adding to the weight theory is attractive but erroneous. The TV has the same number of electrons in it whether it is on or off, it's just that when it's on they are moving.

...and therefore have more energy, and therefore weigh more.

E=mc^2, dude! Not erroneous at all.

That would be the energy that would be released if all of the mass of the electron was converted to energy this is not related to the Kinetic Energy, which, due to the fact that electrons in a circuit move very slowly (can't remember the QI episode) is very very small. KE = 1/2mv^2, considering the mass of an electron is 9.10938188 × 10-31 kg, this coupled with a slow speed squared it multiplies out to not very much.

 726444.  Thu Jul 08, 2010 10:27 am It is related to the kinetic energy. It's related to any energy. E stands for "Energy", "not some particular types of energy but not others". Note the original post on this thread mentions an increase in mass "however marginal". Just because the increase in mass is vanishingly small doesn't mean it's not real.

 726445.  Thu Jul 08, 2010 10:37 am It may well stand for energy, but the energy possessed by an electron cannot be equated to mass, this can only happen if the electron is travelling close to the speed of light, then you can use the relativistic Energy equation. KE = mc^2-Mc^2 (M here is moree normally expressed as m subscript 0 and is the rest mass) In any event electrons conducting current don't approach relativistic speeds.

726562.  Thu Jul 08, 2010 3:07 pm

 Efros wrote: In any event electrons conducting current don't approach relativistic speeds.
They'd have difficulty setting off a speed camera...

 726594.  Thu Jul 08, 2010 4:49 pm Even one set up specifically for Little Tike's cars.

726683.  Fri Jul 09, 2010 5:54 am

 Efros wrote: It may well stand for energy, but the energy possessed by an electron cannot be equated to mass

Yes it can. Any energy can be equated to mass, because it's all one and the same thing. That's the whole point of E=mc^2.

 Efros wrote: this can only happen if the electron is travelling close to the speed of light, then you can use the relativistic Energy equation.

How close? At what proportion of the speed of light do relativistic equations suddenly become valid? Where is this magical cut-off point? More importantly, how do the electrons know that they should suddenly stop obeying Newtonian mechanics and start obeying relativistic laws instead?

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