Re: problem with physical constants (bug?)
- To: mathgroup at smc.vnet.net
- Subject: [mg59249] Re: problem with physical constants (bug?)
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Wed, 3 Aug 2005 01:19:52 -0400 (EDT)
- Organization: The Open University, Milton Keynes, U.K.
- References: <dcmur3$go2$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Chris Chiasson wrote: > Dear MathGroup, > The electric constant is 1/(c^2*magnetic constant). The speed of light > is exact. The magnetic constant is exact. Thus, the electric constant > is exact. In Miscellaneous`PhysicalConstants`, VacuumPermittivity is > not exact. It should be exactly equal to > 1/(SpeedOfLight^2*VacuumPermeability). Hi Chris, No bug here: both quantities are equal except that 1/(SpeedOfLight^2*VacuumPermeability) is expressed in exact arithmetic (in the sense of Mathematica; that is infinite precision numbers: look at the Pi symbol in the definition of VacuumPermeability) whereas VacuumPermittivity is expressed as machine size precision number. So we have: In[1]:= Needs["Miscellaneous`PhysicalConstants`"] In[2]:= VacuumPermittivity Out[2]= (8.854187817*^-12*Ampere*Second)/(Meter*Volt) In[3]:= 1/(SpeedOfLight^2*VacuumPermeability) Out[3]= (625000*Ampere*Second)/(22468879468420441*Meter*Pi*Volt) In[4]:= N[%] Out[4]= (8.85418781762039*^-12*Ampere*Second)/(Meter*Volt) Hope this helps, /J.M.